MS-PS1-4: Modeling Particle Motion, Temperature and Changes of State
In plain English: MS-PS1-4 is the NGSS middle school performance expectation that asks students to develop a model that predicts and describes how particle motion, temperature and state change when thermal energy is added to or removed from a pure substance. Students draw particle models of solids, liquids and gases and read heating and cooling curves. It is usually taught in grade 6, 7 or 8 physical science.
Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
Clarification Statement: Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs. Examples of models could include drawings and diagrams. Examples of particles could include molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium.
Next Generation Science Standards · Disciplinary Core Idea: Matter and Its Interactions · Official standard
Students build and use particle models that explain what happens when thermal energy is added to or removed from a pure substance. A pure substance is matter made of only one kind of particle, such as water, carbon dioxide or helium. A particle here means a molecule (a group of atoms joined together, such as a water molecule) or a single atom that does not join with others, such as a helium atom. Students draw how the particles are spaced and how they move in a solid, a liquid and a gas, predict how the temperature will change, and test the predictions with heating and cooling data.
The NGSS Clarification Statement says: "Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs. Examples of models could include drawings and diagrams. Examples of particles could include molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium." MS-PS1-4 has no official Assessment Boundary. The models on this page stay qualitative: students describe faster or slower particles, closer or farther apart, and read temperatures from data, but they never calculate the energy of a particle. Every data set is invented for teaching and labeled as invented. No student uses an open flame or a hot plate; the one heating demonstration is run by the teacher.
Learning Objectives
By the end of this lesson, students will be able to:
Draw particle models of one pure substance as a solid, a liquid and a gas, showing the spacing and the motion of the particles
Predict how particle motion and temperature change when thermal energy is added to or removed from a substance, including the flat part of the curve during a change of state
Describe with a model what happens to water, carbon dioxide and helium when they are warmed or cooled
Use temperature-time data as evidence for when a substance is changing state, and use it to test a model
Prior Knowledge Required
Students should already be comfortable with:
Matter is made of particles too small to be seen 5-PS1-1
Energy can move from place to place, for example as heat from a warmer object to a cooler one 4-PS3-2
Reading a thermometer in degrees Celsius, including temperatures below zero
Making and reading a line graph with time on the horizontal axis
Show a photo of a frozen puddle on a winter morning and the same puddle melted at noon. Ask students to sketch before any discussion:
Warm-Up Prompt
"Imagine you could zoom in until you see the water particles. Draw what the particles look like in the frozen puddle and in the melted puddle. What changed: the particles themselves, the way they move, or both?"
Collect a few sketches without correcting them. Some students draw the particles in ice as smaller or colder-looking, or draw them melting. Keep the sketches: in Closure students compare them with the model they build today.
Direct Instruction15-20 minutes
Key words.Thermal energy is the energy a substance has because its particles are moving. Kinetic energy is energy of motion: faster particles have more of it. Temperature is a measure of the average kinetic energy of the particles, so a higher temperature means faster particles on average. A state is the form a substance takes: solid, liquid or gas. A change of state is a switch from one state to another: melting (solid to liquid), freezing (liquid to solid), boiling (liquid to gas, with bubbles forming throughout the liquid), condensing (gas to liquid) and sublimation (solid straight to gas).
The model. Use Diagram 1. When thermal energy is added, the particles move faster and the temperature rises, until the particles have enough energy to change how they are arranged. While a change of state is happening, the added energy goes into rearranging the particles, so the temperature stays the same. When thermal energy is removed, everything runs the other way. The particles never change size or shape: only their speed and spacing change.
Thermal energy added: an ice cube on the counter (water)
An ice cube comes out of a freezer at -18 °C and sits on a kitchen counter in a room at 22 °C.
Result: Model: the water molecules vibrate faster and the temperature rises to 0 °C. While the cube melts, the reading stays at 0 °C as the molecules break out of their fixed spots and start sliding past one another. Once all of it is liquid, the temperature climbs toward 22 °C. Total rise: 22 - (-18) = 40 °C.
Thermal energy removed: a fogged mirror (water)
After a hot shower, tiny drops of water cover the bathroom mirror.
Result: Model: water vapor (water as a gas) has fast molecules that are far apart. When they hit the cooler mirror, thermal energy moves from the vapor into the glass, the molecules slow down and gather close together, and the gas condenses into liquid drops.
Solid straight to gas: dry ice (carbon dioxide)
In a teacher demonstration, a few pieces of dry ice (solid carbon dioxide) sit on a tray in a 21 °C room. The teacher handles them with insulated gloves and tongs; students watch from their seats.
Result: Model: at ordinary air pressure, carbon dioxide does not melt. Thermal energy from the room lets the vibrating molecules escape straight into the air as a gas (sublimation), and no puddle forms. The solid stays at about -78 °C while it sublimes; the gas then warms to the room, a rise of 21 - (-78) = 99 °C.
No change of state: a helium balloon in a hot car (inert atoms)
A helium balloon is left in a parked car. The air inside the car warms from 25 °C to 55 °C on a sunny afternoon. Helium atoms do not join with other atoms, so each particle is a single atom.
Result: Model: the helium atoms speed up, hit the inside of the balloon harder and more often, and push it outward, so the balloon grows a little. The temperature rises by 55 - 25 = 30 °C, but helium stays a gas: it would have to be cooled to about -269 °C to become a liquid.
After each example, ask: "Was thermal energy added or removed? What happened to the particle speed? Did the temperature change, stay the same, or both, one after the other?" Then show Diagram 2 and ask which lettered parts are changes of state.
Guided Practice15 minutes
The teacher warms 200 g of crushed ice in a beaker on a hot plate at the front of the room, stirring and reading a thermometer every 2 minutes. Students stay behind a taped safety line. If you cannot run the demonstration, use the invented data below, which match what a steady hot plate gives at sea level.
Guided practice data (invented): 200 g of crushed ice warmed steadily
Time (min)
Temperature (°C)
What you see
0
-10
Dry, frosty ice
2
0
Ice with a little water
4
0
Ice and water
6
0
Mostly water, some ice
8
0
A few small pieces of ice
10
14
All liquid
12
35
All liquid
14
54
All liquid
16
75
Small bubbles on the bottom
18
94
Steam above the water
20
100
Bubbling everywhere
22
100
Bubbling everywhere
Plot temperature against time and connect the points. Compare the shape with Diagram 2.
Label each part of the graph with the state or states present: solid, solid and liquid, liquid, liquid and gas.
For the flat part at 0 °C, write what the added energy is doing to the molecules. Repeat for the flat part at 100 °C.
Between 10 and 18 minutes, the temperature rises by about 10 °C every minute. Use the particle model to explain why it rises here but not between 2 and 8 minutes.
Predict: if the teacher kept heating for 10 more minutes, what would the thermometer read, and what would happen to the amount of water in the beaker?
Independent Practice10-15 minutes
Before showing the data, ask each student to sketch a prediction: a 500 mL bottle of water at 20 °C goes into a home freezer at -18 °C overnight, with a temperature probe inside. Then show the invented readings.
Independent practice data (invented): 500 mL of water in a -18 °C freezer, read every hour
Time (h)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Temperature (°C)
20.0
5.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
-8.1
-14.4
-16.7
Students compare the data with their sketch, mark where thermal energy is leaving the water while the temperature stays the same, and draw particle models of the water at hour 1, hour 6 and hour 13. Ask: "Why does the reading not go below -18 °C, no matter how long the bottle stays in?"
Closure10 minutes
Exit ticket: "A student holds a snowball in a gloved hand, and it slowly turns to slush. Predict the reading of a thermometer pushed into the slush, and say what happens to the reading once only water is left in the glove. Draw the particles for both." (About 0 °C while any snow remains; after that the reading rises as the water warms.) Hand back the warm-up sketches and ask students to correct one thing in their drawing using today's model.
Differentiation Strategies
For Struggling Students
Give a card with three empty boxes labeled solid, liquid and gas, plus a word bank: vibrate, slide, fly, close together, far apart, faster, slower
Start with the ice cube example and act it out with the human particle model before drawing it on paper
Give the graph axes already drawn and labeled, so students only plot the points and label the flat parts
For Advanced Students
Use Diagram 2 to compare the energy needed to melt 1 g of ice with the energy needed to boil 1 g of water, and explain with the model why boiling takes more
Research why water can stay liquid a little below 0 °C before the first ice crystals form, and add that to their cooling-curve model
Extension (beyond this standard): find out why water boils below 100 °C high in the mountains, and explain it with particles hitting the surface of the water
Assessment Guidance
What to Look For
Check that every particle drawing keeps the particles the same size in every state and changes only the spacing and the motion marks. Listen for students who say the temperature keeps rising while a substance melts or boils, and for students who think particles stop moving when a substance freezes. Strong answers name the direction of the energy (added or removed) and link it to faster or slower particles before they mention the state.
02
Classroom Activities
3 Activities
1
Freeze It: A Cooling-Curve Lab
25 minGroups of 3
Groups freeze a small amount of water in a cold bath made of crushed ice and table salt, read the temperature every minute, and build a cooling curve. Then they draw particle models for each part of the curve.
Procedure
Safety: wear goggles. An ice and salt bath gets much colder than ice alone (about -15 °C), so do not hold your hand in it, and wipe up salty water right away. Use plastic test tubes and digital thermometers, never mercury thermometers.
Fill a foam cup with crushed ice, stir in 3 big spoonfuls of salt, and add a splash of water.
Put 5 mL of tap water in a plastic test tube with the thermometer probe in it. Record the starting temperature, then push the tube into the bath.
Read the temperature every minute for 16 minutes. Gently move the probe up and down until the water starts to freeze, then leave it still.
Sample Data (invented)
Minutes 0 to 16: 20.0, 7.4, 1.2, -1.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -5.2, -9.8, -12.4 °C. The first ice crystals appeared at minute 4.
Discussion Questions
For how many readings in a row did the thermometer show 0.0 °C? What was happening to the water during that time?
At minute 3 the water was below 0 °C but still liquid. When the first crystals formed, the reading jumped up to 0.0 °C. Use the model to suggest where that energy came from.
Thermal energy left the water the whole time. Why did the temperature stop falling for about 10 minutes?
Draw the water molecules at minute 1, minute 8 and minute 16.
Modification for Distance Learning
Students freeze a small cup of water in a home freezer and read it with a kitchen thermometer every 15 minutes, or graph the sample data above, then post their cooling curve and three particle drawings.
2
Be the Particles: A Human Model
15 minWhole class
Students act as the molecules of a sample of water while the teacher taps a drum or a box. A faster beat means more thermal energy. The class then critiques its own model: what it shows well and what it gets wrong.
Procedure
Mark a square on the floor with tape. Twelve students stand inside it, shoulder to shoulder, as ice. On a slow beat they sway in place without moving their feet.
Speed up the beat. At a signal, the solid melts: students may shuffle past one another but must keep touching a neighbor.
Speed up again. At the next signal the water boils: students walk quickly in straight lines inside a much larger taped area, changing direction only when they meet a wall or another student. Walking only, no running.
Run it backward: slow the beat, condense, then freeze.
Discussion Questions
When the beat got faster but nobody changed state yet, what did that stand for on a heating curve?
In our model, students stood still between beats. Do real particles in a solid ever stop moving? How would you fix the model?
Helium atoms do not join with other atoms. How would you change the rules to model a helium balloon in a hot car?
Variation: Carbon Dioxide Rules
Run the model again as dry ice. Students must decide what to do when the beat speeds up: since carbon dioxide does not melt at ordinary air pressure, the solid group breaks up straight into walking gas particles.
3
Model Stations: Water, Carbon Dioxide and Inert Atoms
25 minGroups of 3-4
Three stations each describe a real situation with an invented observation card. At each station, groups draw a before and after particle model, say whether thermal energy was added or removed, and predict what a thermometer would show. Groups rotate every 7 minutes.
Station Cards
Station 1, a frozen lake in spring (water): in March the ice on a lake is 20 cm thick and the water under it is about 2 °C. By April the ice is gone and the surface water is 6 °C.
Station 2, liquid helium in a hospital scanner (helium): an MRI scanner keeps its magnet cold with liquid helium at about -269 °C. If the cooling system stops, the helium slowly warms and boils away into a vent pipe.
Station 3, argon for welding (inert atoms): argon atoms, like helium atoms, do not join with other atoms. A gas company cools argon from 20 °C until it becomes a liquid at about -186 °C so that more of it fits in a tank.
Discussion Questions
At Station 1, what does the thermometer read in the thin layer of water touching the bottom of the melting ice? Explain with the model.
Stations 2 and 3 both involve inert atoms. In which station is thermal energy added, and in which is it removed?
Of the two inert gases, which one must be made colder before it turns into a liquid? Use the two temperatures on the cards.
Modification for Distance Learning
Post each card as a slide. Students draw their models on paper, photograph them and upload them to a shared class folder, with one sentence for each station.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Particle Model of a Solid, a Liquid and a Gas
The same pure substance in three states. Adding thermal energy (arrows to the right) speeds the particles up until the solid melts and then the liquid boils; removing it (arrows to the left) slows them until the gas condenses and the liquid freezes. The gas box shows only a few particles, because in a gas they are spread far apart.
Diagram 2: Heating Curve for 1 g of Water at Sea Level
Drawn to scale from standard values: warming ice takes about 2.1 J per gram per °C, melting takes 334 J per gram, warming liquid water takes about 4.18 J per gram per °C, boiling takes 2,260 J per gram and warming steam takes about 2.0 J per gram per °C. The two flat parts (B and D) are changes of state: energy is added but the temperature does not rise.
04
Homework Assignment
~30 min
MS-PS1-4 Homework: Particles, Temperature and State
Directions: All data are invented for practice. Draw particle models as boxes with circles: keep the circles the same size in every drawing and use short lines to show motion. For every problem, say whether thermal energy is added or removed.
Part 1: Build a Particle Model (Problems 1-2)
A shallow pond is at 3 °C at sunset. By sunrise, after a very cold night, the top of the pond is ice at -4 °C. (a) Draw a particle model of the pond water at sunset and of the ice at sunrise. (b) Describe how the motion of the water molecules changed during the night. (c) Predict what a thermometer at the surface read while the ice was forming. (d) Was thermal energy added to the pond or removed from it?
A student watches water boil in an electric kettle for 3 minutes before it switches off. She says: "The kettle keeps adding energy, so the water must get hotter and hotter while it boils." (a) Is she right about the temperature? (b) Use a particle model of the liquid and the steam to explain where the added energy goes while the water boils.
Part 2: Use Data to Test a Model (Problems 3-4)
In a teacher demonstration, a few grams of the metal gallium in a closed zip-top bag are placed in warm water. Readings every minute from minute 0 to minute 8: 20.8, 24.1, 27.3, 29.8, 29.8, 29.8, 29.8, 31.9, 33.7 °C. (a) At what temperature does gallium melt, according to the data? (b) Between which minutes was it melting? (c) What was the average rise in temperature per minute from minute 0 to minute 3? (d) Draw the gallium atoms at minute 1 and at minute 8.
A block of ice from a -25 °C freezer is warmed steadily in a beaker until the water has boiled for 5 minutes, at sea level. (a) Sketch the temperature-time graph you predict and label both flat parts with their temperatures. (b) By how many degrees does the temperature rise from the start until boiling begins? (c) Draw the particles in each flat part.
Part 3: Other Substances and Model Critique (Problems 5-6)
On a clear winter night, frost forms on a car window: water vapor in the air changes straight into tiny ice crystals without becoming liquid first. (a) Is thermal energy added to the water vapor or removed from it? (b) Draw the water molecules before and after. (c) Name the change of state that runs the other way, solid straight to gas, and give one substance from this lesson that does it at ordinary air pressure.
A classmate drew this model of a balloon of neon gas, whose particles are single atoms, being cooled in a freezer: big circles far apart at room temperature, then smaller circles packed together at the bottom of the balloon, with the caption "the atoms shrink and stop moving." (a) Name two things that are wrong with this model. (b) Describe a corrected model of neon in the freezer. (c) Neon becomes a liquid at about -246 °C. Does it turn into a liquid in a home freezer at -18 °C? Explain.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Particle Models
Same-size particles; spacing and motion marks match each state; before and after drawings are labeled
Drawings show the states but particles change size or motion is missing
Energy, Motion and Temperature
Says whether energy is added or removed and links it to faster or slower particles and to the temperature, including the flat parts
Direction of energy is right but the temperature during a change of state is wrong or missing
Use of Data
Reads temperatures and times correctly from the data and uses them as evidence for the model
Reads the data with one error, or reads it without linking it to the model
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data are invented for practice. Choose one answer for each multiple-choice question; your score updates as you answer, and Reset quiz clears everything so you or your students can try again. Short-answer questions show a model answer.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which description fits the particles of liquid water?
Answer: C
In a liquid the particles stay close together but can slide past one another, which is why a liquid can be poured. Choice A describes a solid and choice B describes a gas. Choice D is wrong for every state: particles are always moving.
Question 2 of 20 · Multiple Choice
A block of ice at -12 °C is placed in a room at 20 °C. Before any of the ice melts, what happens?
Answer: A
Thermal energy flows from the warmer room into the ice, so the molecules vibrate faster and the temperature rises toward 0 °C. Choice B forgets that temperature measures the average motion of the particles, so faster particles mean a higher reading. Choice C reverses the link between motion and temperature.
Question 3 of 20 · Multiple Choice
Crushed ice is warmed steadily. While the ice is melting and stirred, the thermometer in the ice and water reads:
Answer: B
During melting, the added energy frees molecules from their fixed spots instead of speeding them up, so the reading stays at about 0 °C until the last ice is gone. Choice A treats melting as ordinary warming. Choice D describes what happens only after all the ice has melted.
Question 4 of 20 · Multiple Choice
A helium balloon is moved from a 22 °C room into a freezer at -18 °C. Which prediction fits a particle model?
Answer: D
Removing thermal energy slows the helium atoms, so they push on the balloon less hard and less often, and the balloon gets smaller. Choice A is a common error: the atoms do not change size. Choice B is wrong because helium stays a gas far below -18 °C. Choice C reverses the direction of the energy.
Question 5 of 20 · Multiple Choice
Which change of state happens when enough thermal energy is removed from liquid water?
Answer: C
Removing energy slows the molecules until they settle into fixed spots: the liquid freezes. Melting and boiling (choices A and B) need energy to be added. Sublimation (choice D) is solid to gas, also with energy added.
Question 6 of 20 · Multiple Choice
Teacher data (invented): lauric acid, a pure substance, cools in a cup. Readings each minute from minute 0 to minute 8: 60, 52, 46, 44, 44, 44, 44, 40, 35 °C. During which minutes was it freezing?
Answer: B
The reading stays at 44 °C from minute 3 to minute 6 even though energy keeps leaving the cup, which is the sign of a change of state. Before minute 3 the liquid was cooling (choice A), and after minute 6 the solid was cooling (choice C). Choice D ignores the flat part.
Question 7 of 20 · Multiple Choice
A thermometer reading tells you which of these?
Answer: A
Temperature measures the average kinetic energy (motion energy) of the particles. It does not depend on how many particles there are (choice B), particles do not change size (choice C), and mass is a different quantity (choice D).
Question 8 of 20 · Multiple Choice
In a teacher demonstration, dry ice is dropped into a bowl of warm water and a thick white fog pours over the rim. What is the white fog?
Answer: C
The very cold carbon dioxide gas cools the water vapor above the warm water. Thermal energy is removed from the vapor, its molecules slow down and condense into tiny liquid drops, which we see as fog. Choice A is wrong because carbon dioxide does not form a liquid at ordinary air pressure. Choice B is wrong because carbon dioxide gas is invisible. Choice D is wrong because nothing is burning.
Question 9 of 20 · Multiple Choice
At a mountain cabin, water in an open pot starts to boil when the thermometer reads 94 °C. The stove keeps adding thermal energy for 5 more minutes. What does the thermometer in the water read at the end?
Answer: D
While the water boils, the added energy lets molecules escape as steam instead of speeding them up on average, so the liquid stays at its boiling temperature, 94 °C here. Choice A uses the sea-level boiling temperature, which the stem does not describe. Choice B adds 1 °C for each of the 5 minutes, as if the temperature kept rising during a change of state. Choice C would mean energy had been removed.
Question 10 of 20 · Multiple Choice
Krypton is made of single atoms that do not join with other atoms. A student draws liquid krypton, then draws the krypton gas that forms when the liquid boils. Compared with the liquid, which drawing of the gas fits the particle model?
Answer: B
When the liquid boils, the same krypton atoms move far apart and keep moving fast; they do not change size. Choice A makes the atoms grow, which never happens in a change of state. Choice C keeps the atoms touching, which shows a liquid, not a gas. Choice D leaves out motion, but particles are always moving, and gas particles move fastest.
Question 11 of 20 · Multiple Choice
Ice at -6 °C is warmed until it has all melted and the water reaches 9 °C. By how many degrees did the temperature rise in all?
Answer: C
The temperature rises from -6 °C to 0 °C (6 degrees), stays at 0 °C while the ice melts, then rises from 0 °C to 9 °C (9 more degrees): 6 + 9 = 15 °C. Choice A subtracts 6 from 9 as if both temperatures were above zero. Choices B and D count only one of the two rising parts.
Question 12 of 20 · Multiple Choice
Drops of water form on the outside of a cold water bottle on a humid day. Which particle change explains the drops?
Answer: D
Water vapor in the air touches the cold bottle, loses thermal energy, slows down and condenses into liquid. Choice A cannot happen through a closed bottle. Choice B is wrong because particles do not turn into a different substance when they change state.
Question 13 of 20 · Multiple Choice
Neon is made of single atoms that do not join with other atoms. A sample of neon gas is warmed from 20 °C to 60 °C. What happens to the neon atoms?
Answer: A
Adding thermal energy raises the temperature, so the atoms move faster on average. Choice B is wrong because neon atoms do not join with other atoms. Choice C repeats the size error, and choice D reverses the direction: neon becomes a liquid only when it is cooled to a very low temperature.
Question 14 of 20 · Multiple Choice
A sample of helium gas is cooled steadily from 20 °C to -100 °C. Which shape does its temperature-time graph have?
Answer: A
Helium stays a gas until about -269 °C, so no change of state happens in this range and the temperature simply keeps falling as energy is removed. Choice B uses the freezing temperature of water, and choice C uses the temperature at which carbon dioxide changes state: each substance has its own. Choice D would mean no energy was removed.
Question 15 of 20 · Short Answer
Describe a particle model of water at 50 °C and at 110 °C (steam). Say how the spacing and the motion of the molecules differ.
At 50 °C the water is a liquid: the molecules are close together and slide past one another. At 110 °C it is steam, a gas: the same molecules are far apart and move much faster in straight lines until they hit something. The molecules are the same size in both.
Question 16 of 20 · Short Answer
Two beakers of ice at 0 °C sit on identical heaters. The beaker with 150 g of ice takes 12 minutes to melt completely. Predict how long a beaker with 50 g of ice at 0 °C takes to melt, and what its thermometer reads while it melts.
One third of the ice needs one third of the energy, so it takes about 12 ÷ 3 = 4 minutes. The thermometer reads about 0 °C the whole time it is melting, the same as for the bigger beaker: the amount changes how long the flat part lasts, not its temperature.
Question 17 of 20 · Short Answer
A glass of water with ice cubes is left on a table in a 24 °C room. Predict the temperature of the water after 15 minutes, while ice is still floating, and after 3 hours. Describe the water molecules at each time.
After 15 minutes: about 0 °C, because energy from the room is melting the ice instead of warming the water. After 3 hours: close to 24 °C, because once the ice is gone the added energy speeds up the molecules. At 15 minutes the molecules in the ice vibrate in place and those in the water slide past one another; at 3 hours all are liquid and moving faster than before.
Question 18 of 20 · Short Answer
Carbon dioxide gas at 20 °C is cooled steadily at ordinary air pressure. Describe what happens to the molecules as it cools, and predict what forms at about -78 °C.
As thermal energy is removed, the carbon dioxide molecules slow down and the temperature falls. At about -78 °C they come close together and lock into fixed spots, forming solid carbon dioxide (dry ice) directly, with no liquid in between, because at ordinary air pressure carbon dioxide skips the liquid state.
Question 19 of 20 · Short Answer
A classmate says: "When ice melts, the water particles melt too, and they get softer." Use a particle model to correct this statement.
The particles themselves do not melt or change. Melting is a change in how the particles are arranged and how they move: in ice they vibrate in fixed spots, and as energy is added they break free and slide past one another. Each water molecule is the same before and after.
Question 20 of 20 · Short Answer
While water boils, energy is still being added, yet the temperature stays the same. Explain why with a particle model.
During boiling the added energy goes into separating the molecules from the liquid so they can escape as a gas, not into making them move faster on average. Since temperature measures average motion, the temperature stays constant until all the liquid has become gas.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-PS1-4 mean?
MS-PS1-4 asks middle school students to build a model that predicts and describes how particle motion, temperature and state change when thermal energy is added to or removed from a pure substance. The code means Middle School, Physical Science, core idea 1 (Matter and Its Interactions), performance expectation 4. The model is usually a drawing or a diagram of particles.
What grade is MS-PS1-4 taught in?
It is a grades 6-8 standard, so each school or state chooses the year. It is often placed in grade 6 or 7 physical science, in a unit on matter or on thermal energy. It works best after students know that matter is made of tiny particles (5-PS1-1).
Does MS-PS1-4 have an assessment boundary?
No, MS-PS1-4 has no official Assessment Boundary. The Clarification Statement points to qualitative models of solids, liquids and gases, so tests usually ask students to draw, compare or explain particle models and to read heating or cooling data, not to calculate energies.
What is the difference between thermal energy and temperature?
Temperature is a measure of the average motion energy of the particles, and thermal energy is the total energy the particles have from their motion. A bathtub of warm water and a cup of the same water have the same temperature, but the bathtub holds far more thermal energy because it has far more particles.
Why does the temperature stop rising while ice melts?
Because the added energy is used to free the molecules from their fixed spots, not to speed them up on average. The thermometer shows 0 °C until the last ice is gone. This flat part of a heating or cooling curve is the best evidence students can collect that a change of state is happening.
Why does dry ice not melt?
At ordinary air pressure, solid carbon dioxide cannot exist as a liquid, so it changes straight from solid to gas. This is called sublimation, and it happens at about -78 °C. Liquid carbon dioxide exists only under much higher pressure, for example inside some fire extinguishers. Dry ice is for teacher demonstrations: it can burn skin, so it is handled with insulated gloves and tongs and is never put in a closed container.
What kinds of models count for MS-PS1-4?
The Clarification Statement names drawings and diagrams. Good models show particles of one size, use spacing to show the state and use motion lines or arrows to show speed, and they come in pairs or sets (before and after, or solid, liquid and gas). Physical models, such as students acting as particles, also work if the class discusses what the model gets wrong.
What mistakes do students often make with particle models?
Many students draw particles that grow when heated, shrink when cooled, or stop moving in a solid. Others think the temperature keeps rising while a substance boils. Ask students to keep every particle the same size and to add motion lines to every drawing, including the solid.
Are the labs for MS-PS1-4 safe for middle school?
Yes, when they use ice, salt and water. An ice and salt bath can reach about -15 °C, so students wear goggles and keep their hands out of it. Students never use flames or hot plates in this lesson: any heating of water and all dry ice handling are done by the teacher.
How does MS-PS1-4 connect to high school science?
In high school, HS-PS3-2 asks students to model thermal energy as the motion of particles, and HS-PS3-4 asks them to investigate how thermal energy spreads when warm and cool objects are combined. Chemistry courses later add the forces between particles and the energy needed for each change of state, which builds on the flat parts of the heating curve.
07
Related Standards
5 standards
These standards connect to MS-PS1-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-PS1-1Prerequisite
Develop a model to describe that matter is made of particles too small to be seen
Lesson coming soon
Alongside
MS-PS3-4Parallel
Plan an investigation linking energy transferred, type of matter, mass and particle motion
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