HS-PS1-5: Explaining Reaction Rates with Temperature, Concentration and Collisions
In plain English: HS-PS1-5 is the NGSS high school performance expectation that asks students to use evidence and scientific principles to explain how changing the temperature or the concentration of reacting particles changes how fast a reaction goes. Explanations focus on the number and energy of collisions between particles. It is usually taught in Chemistry or Physical Science.
Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
Clarification Statement: Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.
Assessment Boundary: Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.
Next Generation Science Standards · Disciplinary Core Idea: Matter and Its Interactions · Official standard
Students explain why reactions speed up when the reacting particles are warmer or more concentrated. They use the collision model: particles react only when they collide, and only when the collision has at least a minimum amount of energy. Raising the concentration packs more particles into the same space, so they collide more often. Raising the temperature makes particles move faster, so they collide more often and a larger share of the collisions has enough energy. Students analyze rate data, build particle models and plan fair tests.
The NGSS Clarification Statement says: "Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules." The Assessment Boundary says: "Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature." Every reaction on this page has two reactants, conclusions about temperature stay qualitative (faster or slower, not a formula), and catalysts and surface area are left for later (beyond this standard). All data sets are invented for teaching. Student labs use only household-strength materials with goggles; the one acid reaction is a teacher demonstration.
Learning Objectives
By the end of this lesson, students will be able to:
State the conditions for a reaction: reacting particles must collide, with at least a minimum energy
Use rate data to describe how increasing the concentration of a reactant changes the rate of a reaction
Use rate data to describe qualitatively how increasing temperature changes the rate of a reaction
Explain each effect in terms of the number of collisions per second and the energy of those collisions
Plan a fair test that changes one variable (temperature or concentration) and keeps the others the same
Prior Knowledge Required
Students should already be comfortable with:
Temperature is related to the average kinetic energy of particles MS-PS1-4
Recognizing a chemical reaction from data on properties before and after MS-PS1-2
Concentration as the amount of a substance dissolved in a given volume
Reading data tables and line graphs, and finding a rate as a change divided by a time
Teacher demonstration: drop a quarter of an effervescent vitamin C tablet into a clear cup of ice water and another quarter into a cup of warm tap water at the same moment. Students watch the fizzing. (The tablet holds two reactants, citric acid and sodium bicarbonate, which react once they are wet and give off carbon dioxide.)
Warm-Up Prompt
"Both pieces hold the same two reactants. Why does one fizz so much faster? Draw what the particles might be doing in each cup, and write one question you would need to test to be sure."
Collect ideas. Students often say "heat gives it energy" without saying what the particles do. Keep a list of their words on the board and return to it after the collision model.
Direct Instruction15-20 minutes
The collision model. Particles of two reactants can react only when they collide, and only if the collision has at least a minimum energy (and a suitable orientation). Most collisions do not have enough energy and the particles just bounce apart. The rate of a reaction is how much reactant is used up, or product is made, per unit time. Anything that gives more collisions with enough energy per second makes the reaction faster.
Concentration: more particles in the same volume collide more often, so there are more collisions with enough energy each second. The energy of each collision does not change.
Temperature: warmer particles move faster. They collide more often, and a larger share of the collisions has at least the minimum energy (Diagram 2). The second effect is the larger one.
Particle model of concentration
Box 1 holds 3 particles of reactant A and 3 of reactant B. Box 2 is the same size and holds 6 A and 3 B, at the same temperature.
Result: Possible A-B pairings: 3 × 3 = 9 in Box 1 and 6 × 3 = 18 in Box 2. Doubling the number of A particles doubles the chances for A-B collisions, so Box 2 reacts faster. Each collision has the same energy in both boxes.
Temperature evidence
A calcium carbonate antacid tablet is dropped into 100 mL of vinegar (two reactants: calcium carbonate and acetic acid). At 10 °C it stops fizzing after 240 s; at 30 °C it stops after 90 s. (Invented data.)
Result: Higher temperature, shorter time, so the rate is greater. The warmer acid particles move faster, hit the tablet more often and more of the hits have enough energy to react.
Concentration evidence
1.0 g of baking soda is added to 50 mL of vinegar at full strength, half strength and quarter strength (diluted with water, all at 22 °C). Gas collected in the first 10 s: 42, 21 and 11 mL. (Invented data.)
Result: Average rates: 4.2, 2.1 and 1.1 mL/s. Stronger vinegar has more acetic acid particles per mL, so the solid is hit more often each second and the reaction is faster.
Energy of collisions
Why can a modest rise in temperature give a clearly faster reaction? Use Diagram 2.
Result: The minimum energy stays the same, but at the higher temperature the curve spreads to higher energies, so the shaded share of collisions above the minimum is larger. Both more collisions and a larger share with enough energy add to the rate.
After each example ask: "Is the change mostly in the number of collisions, the energy of collisions, or both?" Remind students that the Assessment Boundary keeps the temperature relationship qualitative: say "faster" or "slower" and explain why, rather than predicting an exact rate.
Guided Practice15 minutes
Pairs analyze invented data from a teacher demonstration: 0.06 g of magnesium ribbon reacts with 50 mL of hydrochloric acid (two reactants: magnesium and hydrogen chloride) at 1.0 M and at 0.5 M, both at 22 °C. The teacher wears goggles, uses dilute acid and keeps all flames away because the gas is hydrogen. Diagram 1 shows the same data.
Guided practice data: hydrogen collected (mL)
Time (s)
0
10
20
30
40
50
60
1.0 M acid
0
16
30
41
49
54
56
0.5 M acid
0
8
15
22
28
33
37
Find the average rate in the first 10 s for each concentration (1.6 mL/s and 0.8 mL/s).
Describe how the rate changes over time for the 1.0 M acid, and use collisions to explain why the curve levels off.
Both runs use the same 0.06 g of magnesium, with the acid in excess. Predict whether the 0.5 M run will end with more, less or the same volume of gas, and explain.
Write a claim-evidence-reasoning statement about concentration and rate that cites one number from the table.
Independent Practice10-15 minutes
Each student analyzes an invented temperature data set and writes a claim, evidence and reasoning paragraph. The same mass of baking soda (1.0 g) is added to 50 mL of full-strength vinegar at three temperatures.
Independent practice data: baking soda and vinegar
Vinegar temperature (°C)
10
25
40
Time until fizzing stops (s)
48
30
19
The claim should state the direction of the relationship, the evidence should cite the times, and the reasoning should name both the number and the energy of collisions. Remind students not to claim an exact rule such as "the rate doubles every 15 degrees": the data support only a qualitative relationship.
Closure5 minutes
Exit ticket: "Draw two same-size boxes of particles, one with a dilute and one with a concentrated solution of reactant B, each with the same number of reactant A particles. Mark which one reacts faster and write one sentence explaining why." Return to the warm-up list and ask students to rewrite "heat gives it energy" as a collision explanation.
Differentiation Strategies
For Struggling Students
Start with the collision game (Activity 3) before the data, so students have a physical memory of collisions and energy
Give a sentence frame: "When the ___ increases, the particles ___, so there are ___ collisions per second and ___ of them have enough energy."
Use particle-box cards with small numbers of particles so students can count possible A-B pairings directly
For Advanced Students
Ask students to explain why the rate of a reaction slows down as it goes, even at constant temperature
Have students use Diagram 2 to argue why the effect of temperature on rate is usually larger than its effect on the number of collisions alone
Ask students to design a way to measure the rate of a reaction that gives off no gas and changes no color
Assessment Guidance
What to Look For
Strong explanations name both parts of the collision model: how often particles collide and whether the collisions have enough energy. For concentration, students should say that collisions become more frequent while the energy per collision stays the same. For temperature, they should mention both more frequent and more energetic collisions. Watch for the idea that heat makes particles bigger or that concentration makes particles hit harder, and check that investigation plans change only one variable.
02
Classroom Activities
3 Activities
1
Glow Stick Temperature Lab
25 minGroups of 3-4
Groups place identical activated glow sticks in water baths at three temperatures and measure their brightness with a phone light-meter app. Inside a glow stick, two reactants (hydrogen peroxide and an oxalate ester) react, and a dye gives off the energy as light, so brighter light means more reactions per second.
Procedure
Safety: wear goggles. Never cut or break open a glow stick: the liquid irritates skin and eyes. If one leaks, rinse skin with water and tell the teacher. Use ice water and warm tap water only (no hotter than 45 °C); no kettles or hot plates.
Set up three beakers: ice water (about 5 °C), room-temperature water (about 22 °C) and warm tap water (about 40 °C). Record each temperature.
Bend three glow sticks of the same brand and color at the same moment, shake them, and put one in each beaker.
After 2 minutes, dim the room and hold the phone 10 cm from each stick to record the light reading. Keep the distance and angle the same for every reading.
Leave the sticks in the baths and check them again at the end of class.
Sample Data (invented)
Light reading after 2 minutes: 5 °C, 12 lux; 22 °C, 38 lux; 40 °C, 95 lux. At the end of class, the 40 °C stick is the dimmest of the three.
Discussion Questions
Rank the three sticks by reaction rate after 2 minutes. What is your evidence?
Explain the ranking with the number and energy of collisions between the two reactants.
Why is the warm stick the dimmest at the end of class? (Hint: what happened to its reactants?)
Which variables did your group keep the same, and why does each one matter?
Modification for Distance Learning
Students run the lab at home with a glow stick, two mugs of water and a phone, or analyze the sample data and a teacher video.
2
Vinegar Strength and Marble Chips
25 minGroups of 3-4
Groups measure how fast marble chips (calcium carbonate) react with vinegar (acetic acid) at three concentrations. The carbon dioxide escapes, so the mass on the balance goes down, and the mass lost in 5 minutes measures the rate.
Procedure
Safety: wear goggles. Vinegar is a weak acid: rinse any splashes off skin with water, and do not taste anything. Put a loose cotton ball in the neck of the flask to catch spray.
Make three solutions of 50 mL each: full-strength vinegar (5% acetic acid), half strength (25 mL vinegar + 25 mL water, 2.5%) and quarter strength (12.5 mL vinegar + 37.5 mL water, 1.25%). Let them reach room temperature.
Put 5.0 g of similar-sized marble chips in a flask on the balance, add one solution, and record the mass at the start and after 5 minutes.
Repeat for each concentration with fresh chips of the same total mass and size.
Sample Data (invented)
Mass lost in 5 minutes: full strength 0.24 g, half strength 0.13 g, quarter strength 0.06 g. Students compute the average rate in g/min for each.
Discussion Questions
The mass loss drops each time the vinegar is diluted. Use the collision model to explain why.
Why must the chips have the same mass and size, and why must the solutions be at the same temperature?
Does diluting the vinegar change the energy of each collision? Explain.
Challenge Variation
Groups plan, but do not run without teacher approval, a test of the same reaction at two temperatures using the same concentration, and predict the result qualitatively.
3
The Collision Game
20 minWhole class
Students act as particles of reactant A (red card) and reactant B (blue card) walking inside a taped square. Only an A-B collision can react, and only if it has enough energy, which the pair decides with dice.
Rules
Tape a 3 m by 3 m square on a clear floor. Students walk, never run, and "collide" with a gentle elbow tap.
When an A meets a B, each rolls one die. The collision reacts if the total is 10 or more. A-A and B-B collisions do not count.
"Higher temperature": students walk briskly, and each student adds 1 to their roll, so the pair needs a dice total of 8 or more.
A recorder at each side counts collisions and reactions for 60 s. Reacted pairs step out.
Round 1: 4 A and 4 B, slow walk. Round 2: 8 A and 4 B, slow walk. Round 3: 4 A and 4 B, brisk walk with the bonus.
From Round 1 to Round 2 the collisions doubled. Did the share of collisions that reacted change? What does that tell you about concentration?
In Round 3, which two things changed compared with Round 1? Connect each to temperature.
The chance that a pair of dice totals 10 or more is 6 in 36. The chance of a total of 8 or more is 15 in 36. How do these compare with the shares in the sample data?
Where does the game fail as a model of real particles?
Modification for Distance Learning
Students use the free PhET simulation "Reactions & Rates" and record collisions and reactions while changing the number of particles and the temperature.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Hydrogen Collected Over Time at Two Acid Concentrations
Invented teacher-demonstration data, drawn to scale: 0.06 g of magnesium ribbon in 50 mL of hydrochloric acid at 22 °C. The steeper start of the 1.0 M curve shows a faster reaction. The 1.0 M curve levels off toward about 60 mL, the volume of hydrogen that 0.06 g of magnesium can make, while the 0.5 M curve is still rising at 60 s.
Diagram 2: Collision Energies at a Lower and a Higher Temperature
The curves show how collision energies are spread out at two temperatures, computed from the kinetic energy distribution in arbitrary units. The minimum energy needed to react (red line) is the same at both temperatures. At the higher temperature, a larger share of collisions lies above it (shaded), so more collisions each second can react.
04
Homework Assignment
~30 min
HS-PS1-5 Homework: Explaining Reaction Rates
Directions: All data are invented for practice, and every reaction has two reactants. Explain with the number and the energy of collisions. For temperature, describe the relationship in words (faster or slower); you do not need a formula.
Part 1: Temperature Evidence (Problems 1-2)
In a teacher demonstration, zinc granules react with dilute hydrochloric acid. The hydrogen collected in the first 60 s is 12 mL at 15 °C, 25 mL at 25 °C and 48 mL at 35 °C, with the same acid concentration and zinc mass each time. (a) Rank the three rates. (b) Explain the pattern with the number and energy of collisions. (c) Predict, in words, how much hydrogen you would collect in 60 s at 30 °C. Why can you not give an exact value?
Plan an investigation to test how water temperature affects the rate of the reaction in an effervescent vitamin C tablet. Name (a) the variable you change, (b) what you measure, (c) three variables you keep the same, (d) how many trials you run, and (e) two safety steps.
Part 2: Concentration Evidence (Problems 3-4)
Solid baking soda is added to citric acid solutions of three concentrations, all at 20 °C. Gas collected in the first 20 s: 0.50 M, 30 mL; 0.25 M, 15 mL; 0.125 M, 8 mL. (a) Find the average rate for each in mL/s. (b) Describe how the rate changes with concentration. (c) Explain the pattern with collisions.
Three same-size containers at the same temperature hold particles of reactants A and B. Container X: 5 A and 2 B. Container Y: 5 A and 4 B. Container Z: 10 A and 4 B. (a) Count the possible A-B pairings in each. (b) Rank the containers from slowest to fastest reaction. (c) Explain why the energy of the collisions is the same in all three.
Part 3: Explanations and Arguments (Problems 5-6)
A classmate writes: "Heating a reaction makes it faster only because hot particles are bigger, so they bump into each other more." (a) Identify two problems with this explanation. (b) Write a correct explanation that uses both the number and the energy of collisions.
Solutions of two reactants, P and Q, are mixed in four trials. Trial 1: 0.2 M, 20 °C, 80 s to finish. Trial 2: 0.4 M, 20 °C, 40 s. Trial 3: 0.2 M, 35 °C, 30 s. Trial 4: 0.4 M, 35 °C, not yet run. (a) Which two trials show the effect of concentration, and which two show the effect of temperature? (b) Predict, in words, how Trial 4 compares with the other trials. (c) Write a claim-evidence-reasoning paragraph for each variable.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Using Data as Evidence
Rates computed or ranked correctly, and specific values cited
Correct trend with a missing or incorrect value
Collision Reasoning
Names the number of collisions for concentration, and both the number and the energy of collisions for temperature
Names only one part of the collision model
Investigation Design
Changes one variable, keeps the others the same, repeats trials and names safety steps
Plan is incomplete or changes more than one variable
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data are invented, and every reaction has two reactants. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
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
According to the collision model, what must happen for particles of two reactants to react?
Answer: B
Particles react only when they collide, and only if the collision has enough energy (and a suitable orientation). Choice A describes a condition that is often true but does not cause a reaction. Choices C and D are not required: many reactions happen between gases or solids.
Question 2 of 20 · Multiple Choice
A student doubles the concentration of one reactant and keeps the temperature the same. Why does the reaction go faster?
Answer: A
More particles in the same volume means more collisions per second. The temperature is unchanged, so the energy of the collisions is unchanged; choice B confuses concentration with temperature. Choice C describes what a catalyst does (beyond this standard).
Question 3 of 20 · Multiple Choice
Why does raising the temperature make a reaction between two reactants faster?
Answer: D
Warmer particles move faster, which increases both how often they collide and the share of collisions with at least the minimum energy. Choice A is backward. Choice B is a common confusion: the minimum energy stays the same. Choice C describes a change in concentration, not temperature.
Question 4 of 20 · Multiple Choice
An acid reacts with a solid at three concentrations. Gas collected in the first 20 s: 0.25 M, 6 mL; 0.50 M, 12 mL; 1.00 M, 24 mL. What is the average rate at 1.00 M?
Answer: C
Rate = 24 mL ÷ 20 s = 1.2 mL/s. Choices A and B are the rates at 0.25 M and 0.50 M. Choice D is the volume, not the volume per second.
Question 5 of 20 · Multiple Choice
A reaction is timed at four temperatures: 15 °C, 150 s; 25 °C, 90 s; 35 °C, 50 s; 45 °C, 30 s. Which conclusion do the data support?
Answer: B
Every rise in temperature shortens the time, so the rate goes up. Choice D confuses a shorter time with a lower rate. Choice C claims an exact rule the data do not show: the times drop by 60, 40 and 20 s, not by equal amounts, and the standard asks only for the qualitative relationship.
Question 6 of 20 · Multiple Choice
Four same-size boxes at the same temperature hold particles of reactants A and B. Which box should react fastest?
Answer: C
The possible A-B pairings are 16, 16, 36 and 15, so the box with 6 A and 6 B has the most chances for A-B collisions each second. Choice B has the most A particles, but with only 2 B particles it has no more pairings than choice A.
Question 7 of 20 · Multiple Choice
A student keeps a reaction mixture in an ice bath instead of at room temperature. What happens to the rate, and why?
Answer: A
Cooling slows the particles, so there are fewer collisions and a smaller share of them has at least the minimum energy. Choice C ignores the effect of temperature. Choice D invents a change in particle size.
Question 8 of 20 · Multiple Choice
A reaction's rate is fastest at the start and slows down as it continues, even though the temperature stays the same. What is the best explanation?
Answer: D
As reactants turn into products, fewer reactant particles remain in the same volume, so collisions between them become less frequent. Choice A is wrong because the temperature, and so the energy of the particles, stays the same.
Question 9 of 20 · Multiple Choice
A student wants to test how temperature affects the rate of a reaction between two solutions. Which must stay the same in every trial?
Answer: B
In a fair test only the independent variable (temperature) changes, so the concentrations and volumes must be kept the same. Choice A is the variable being tested. Choice C is what is measured.
Question 10 of 20 · Multiple Choice
On a graph of collision energies like Diagram 2, what happens when the temperature is raised?
Answer: A
The curve spreads toward higher energies, so more of the area lies past the fixed minimum energy. Choice B describes a catalyst (beyond this standard). Choice D overstates the change: many collisions still lack enough energy.
Question 11 of 20 · Multiple Choice
A student dilutes 30 mL of an acid with water to a total of 60 mL, so its concentration is halved. The temperature is unchanged. What happens when the same solid is added?
Answer: C
Halving the concentration puts fewer acid particles in each mL, so collisions with the solid are less frequent. Choice A confuses volume with concentration. Choice D is wrong because the temperature, and so the energy per collision, has not changed.
Question 12 of 20 · Multiple Choice
A reaction between two reactants speeds up. Which change could NOT be the cause, according to the collision model?
Answer: D
Cooling makes particles slower, so collisions are less frequent and less energetic, and the rate drops. The other three changes all increase the number of collisions with enough energy per second. Choice B is a real cause: raising the concentration of even one reactant makes A-B collisions more frequent.
Question 13 of 20 · Multiple Choice
Students time a reaction at four temperatures: 10 °C, 120 s; 20 °C, 70 s; 30 °C, 85 s; 40 °C, 25 s. Which trial should they repeat first?
Answer: C
The 30 °C trial took longer than the 20 °C trial, which breaks the pattern of shorter times at higher temperatures shown by the other three. It is the likely measurement error. Picking choice D because it has the shortest time confuses an extreme value with an error.
Question 14 of 20 · Multiple Choice
A student raises the temperature and the concentration at the same time and sees a faster reaction. What is the main problem with the investigation?
Answer: B
Changing two variables at once means the effect of each cannot be separated. A fair test changes only one variable at a time. Choice C contradicts the evidence from temperature data.
Question 15 of 20 · Short Answer
Container 1 holds 5 particles of A and 3 of B. Container 2 is the same size, at the same temperature, and holds 5 A and 6 B. Which reacts faster? Explain with a count and the collision model.
Container 2. It has 5 × 6 = 30 possible A-B pairings, compared with 5 × 3 = 15 in Container 1, so A-B collisions happen about twice as often. The temperature is the same, so the energy of each collision is the same; the rate is greater only because collisions are more frequent.
Question 16 of 20 · Short Answer
A reaction takes 210 s at 12 °C, 110 s at 24 °C and 55 s at 36 °C. Write a claim, evidence and reasoning response about temperature and rate.
Claim: as the temperature increases, the rate of the reaction increases. Evidence: the time falls from 210 s to 110 s to 55 s as the temperature rises from 12 °C to 36 °C. Reasoning: warmer particles move faster, so they collide more often and a larger share of the collisions has at least the minimum energy needed to react.
Question 17 of 20 · Short Answer
A reaction gives off gas: 20 mL in the first 10 s, 14 mL in the next 10 s and 9 mL in the 10 s after that, at constant temperature. Find the average rate in each interval and explain the pattern.
The rates are 2.0, 1.4 and 0.9 mL/s. The reaction slows because the reactants are being used up: their concentration falls, so the reactant particles collide less often. The temperature is constant, so the energy of the collisions does not explain the change.
Question 18 of 20 · Short Answer
A student claims: "Heating a reaction makes it faster because it lowers the minimum energy the particles need to react." Correct the claim.
Heating does not change the minimum energy; it is set by the reaction. Heating makes the particles move faster, so they collide more often and a larger share of the collisions has at least the minimum energy. (Lowering the minimum energy is what a catalyst does, which is beyond this standard.)
Question 19 of 20 · Short Answer
A factory wants a reaction between two dissolved reactants to go faster without changing what it makes. Suggest one change to temperature and one change to concentration, and explain each at the particle level.
Temperature: warm the solutions. The particles move faster, collide more often and more collisions have enough energy. Concentration: use more concentrated solutions of one or both reactants. More particles in the same volume collide more often, with the same energy per collision. Either change alone gives more successful collisions per second.
Question 20 of 20 · Short Answer
Hydrochloric acid at 0.5, 1.0 and 2.0 M reacts with calcium carbonate powder at 20 °C. The times to collect 20 mL of carbon dioxide are 80, 40 and 20 s. Find each average rate and explain the pattern.
The rates are 20 ÷ 80 = 0.25 mL/s, 20 ÷ 40 = 0.5 mL/s and 20 ÷ 20 = 1.0 mL/s. Higher acid concentration gives a faster rate, because more acid particles in each mL hit the solid more often each second; the energy of each collision is the same because the temperature is the same.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-PS1-5 mean?
HS-PS1-5 asks students to explain, using evidence, why a reaction speeds up or slows down when the temperature or the concentration of the reacting particles changes. The explanation is built on collisions: how often particles collide and whether the collisions have enough energy. The code means High School, Physical Science, core idea 1 (Matter and Its Interactions), performance expectation 5.
Is HS-PS1-5 taught in chemistry or physical science?
It is usually taught in a high school Chemistry course, in a unit on reaction rates or kinetics. It also fits Physical Science and integrated science courses, because the reasoning uses particle motion rather than heavy math.
What is the assessment boundary for HS-PS1-5?
Assessment is limited to simple reactions with only two reactants, to evidence from temperature, concentration and rate data, and to qualitative relationships between rate and temperature. Students say that a higher temperature gives a faster reaction and explain why; equations that predict exact rates from temperature are beyond this standard.
What is collision theory in chemistry?
Collision theory says that reacting particles must collide, with at least a minimum energy and a suitable orientation, for a reaction to happen. Anything that increases the number of such successful collisions each second increases the rate.
Do students need the Arrhenius equation for HS-PS1-5?
No. The Assessment Boundary limits the rate-temperature relationship to a qualitative one, so students describe and explain the trend without a formula. Some advanced chemistry courses add the Arrhenius equation later, but it is beyond this standard.
Does HS-PS1-5 include catalysts and surface area?
No. The standard names only temperature and concentration. Catalysts and particle size are important in chemistry, and many teachers mention them, but they are beyond this standard. Keep surface area constant in HS-PS1-5 labs, for example by using chips or tablet pieces of the same size.
What safe labs work for teaching reaction rates?
Classroom-safe choices include glow sticks in water baths, effervescent vitamin C tablets in water at different temperatures, and vinegar of different strengths with marble chips or baking soda. Students wear goggles, use tap water no hotter than about 45 °C and never cut open glow sticks. Reactions with stronger acids, or ones that make flammable hydrogen, are better run by the teacher.
How can students measure a reaction rate in class?
Measure a quantity that changes as the reaction goes, then divide by time. Options include the volume of gas collected in a syringe or an upturned cylinder, the mass lost as a gas escapes, the time for a solid to disappear or for fizzing to stop, and the brightness of light from a glow stick.
Why does HS-PS1-5 use only two reactants?
With two reactants, each collision involves one particle of each, so students can reason directly about how often A meets B. Reactions with more reactants often happen in several steps, which makes the collision explanation more complex. The Assessment Boundary keeps the focus on simple two-reactant systems.
What comes after HS-PS1-5?
HS-PS1-6 uses the same collision reasoning for reversible reactions at equilibrium, where changing a condition changes the forward and reverse rates differently and shifts the amounts of products. HS-PS1-4 connects to the energy side: the hump on an energy diagram is the minimum energy for a collision to react.
07
Related Standards
4 standards
These standards connect to HS-PS1-5: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-PS1-4Prerequisite
Model how particle motion, temperature and state change when thermal energy changes
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
