CHEMISTRY · Stage 9 · Chapter 12: Chemical Reactions 3 and Rates
Chemistry 12.11 Temperature and reaction rate — Particle Kinetic Energy and Collisions
5 min read 6 parts Lesson 11 of 13
Lesson summary
12.11 Temperature and reaction rate — Particle Kinetic Energy and Collisions — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe and explain how temperature affects reaction rate using collision theory.Faster at higher temperatures — reactions go faster at h…
- Rule of thumb
- More frequent collisions
- More successful collisions
- What does not change
- Hypothesis
- Prediction
Section 1 of 6Effect of temperature
- Faster at higher temperatures
- reactions go faster at higher temperatures.
- Potatoes cook in 15 minutes in boiling water at 100 °C but more quickly in boiling oil at 200 °C.
- Food spoils more slowly in a fridge and cooks faster in a hot oven.
- Rule of thumb
- a 10 °C rise roughly doubles the rate for many reactions, although this is not exact.
- Pattern
- as temperature increases, the rate of reaction increases.
Section 2 of 6Explaining with particles
- Kinetic energy
- heating gives particles more kinetic energy, so they move faster.
- More frequent collisions
- faster particles collide more often.
- More successful collisions
- a greater proportion of collisions have energy greater than or equal to the activation energy, so more collisions are effective.
- This second effect is the more important one, because even a small rise in temperature greatly increases the fraction of particles with enough energy.
- What does not change
- particles do not get bigger and the activation energy does not change.
Section 3 of 6Farai's investigation
- Hypothesis
- reactions happen when particles collide, and at higher temperatures particles move faster and collide more frequently,
- so as temperature increases the reaction rate increases.
- Reaction
- sodium thiosulfate + hydrochloric acid → sodium chloride + water + sulfur dioxide + sulfur.
- Sulfur is insoluble, so it forms as a precipitate of tiny solid pieces that make the mixture cloudy.
- Method
- pour sodium thiosulfate solution into a flask placed over a cross, add hydrochloric acid, start a timer and stop it when the cross can no longer be seen.
- At 20 °C the cross disappeared after about 244 seconds.
- Variables
- the independent variable is the temperature of the acid, the dependent variable is the time to cover the cross,
- and the volumes and concentrations are controlled.
- the independent variable is the temperature of the acid, the dependent variable is the time to cover the cross,
- Repeats
- repeat each temperature three times to reduce error and obtain reliable results.
- Prediction
- at higher temperatures the reaction will be quicker, so the cross will disappear after a shorter time.
Section 4 of 6Results and analysis
- Temperatures
- Farai repeated the experiment at 20, 30, 40, 50 and 60 °C and recorded the mean time at each.
- Anomalous result
- the first result at 50 °C was very different from the others, probably because the acid had cooled before use, so he left it out of the mean.
- Graph
- both variables are continuous, so he drew a line graph.
- Conclusion
- the higher the temperature, the faster the reaction, so his prediction and hypothesis were supported.
- Rate from time
- rate = 1 ÷ time, and a graph of rate against temperature curves upward.
- Errors
- judging when the cross disappears is subjective, so using the same observer or a light sensor improves it.
Section 5 of 6Comparing factors that affect rate
| Factor | Collision frequency | Energy of collisions |
|---|---|---|
| Concentration | Higher | Same |
| Surface area | Higher | Same |
| Temperature | Higher | Higher |
| Catalyst | Same | Lower activation energy needed |
- Rate graph
- the curve for a higher temperature starts steeper and reaches the plateau sooner,
- but the final volume is the same if the amounts of reactants are the same.
- Not the same
- reaction rate is not the same as the amount of product.
- Exothermic reactions
- heating them does not stop them working.
Section 6 of 6Applications
- Pressure cookers
- they cook food faster by raising the temperature.
- Refrigerators
- they slow bacteria.
- Industry
- it chooses a temperature that gives a fast rate without wasting energy or risking safety.
- Safety
- handle hot acids and flasks with care.
Last updated: