HS-PS1-5: Temperature, Concentration and Reaction Rate
Also called NGSS HS-PS1-5 · Topic: Chemical Reactions · Physical Science
The Official Wording
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.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-PS1-5 Means in Plain English
High school students use collision theory to explain why a reaction speeds up when the reactants are warmer or more concentrated. They reason about how often particles collide and how many collisions carry enough energy to break bonds, backing the reasoning with rate data.
Reactions involve just two reactants, and the link between rate and temperature stays descriptive, with no rate equations. It builds on particle motion and temperature (MS-PS1-4) and leads into equilibrium design in HS-PS1-6.
HS-PS1-5 I Can Statements
- I can explain reaction rate using particle collisions.
- I can predict how warming a reaction changes its speed.
- I can use rate data as evidence for my explanation.
HS-PS1-5 Worked Example
The classic disappearing X lab, run at four temperatures so the class can see the trend in their own times.
How does temperature change how fast sodium thiosulfate reacts with dilute hydrochloric acid?
Set It Up: Sodium thiosulfate solution, dilute hydrochloric acid, a conical flask, a card marked with a black X, water baths, a thermometer and a stopwatch.
- Warm the thiosulfate to 20 °C, set the flask on the X, add the acid and start timing.Solution turns cloudy with sulfur
- Stop the clock when the X can no longer be seen from above.20 °C: about 60 s
- Repeat at 30, 40 and 50 °C with the same volumes.About 32 s, 17 s and 10 s
- Plot time against temperature and describe the pattern.Each 10 °C rise roughly halves the time
The warmer the solution, the faster the cloud hid the X, with times dropping from about a minute to about ten seconds.
Why it works: Warmer particles move faster, so they collide more often and more of the collisions have enough energy to react.
Common Mistakes with HS-PS1-5
Counting collisions only
“Hotter just means more collisions, that is all.”
Try this: Collisions also hit harder when warm. A larger share of them carries enough energy to break bonds, which is the bigger effect.
Confusing rate with amount of product
Saying the hot flask made more sulfur
Try this: Temperature changes how fast the product forms, not how much. With the same starting amounts, each flask ends with similar cloudiness.
Changing volume along with temperature
Using a bigger pour of acid in the hot trial
Try this: Keep every volume and concentration the same and change only the temperature, so the timing differences have one clear cause.
Where HS-PS1-5 Fits
Practice HS-PS1-5
Quick Check
- Why does milk sour faster on the counter than in the fridge?
- How does doubling the acid's concentration change the reaction rate, and why?
- In the disappearing X lab, what does a shorter time tell you?