
Relationship between temperature and rate of reaction. Image credit bu.edu
ZIMSEC O Level Combined Science Notes:Experiment: The rate of reactions and temperature
Aim: To find the effect of temperature on the rate of reaction: using hydrochloric acid and sodium thiosulphate
Materials: flask, measuring cylinder, stop watch/watch/stop watch app, thermometer with a 0-100°C scale, burner, tripod, sheet of white paper, dilute hydrochloric acid, sodium thiosulphate solution
Methods
- Mark the sheet of paper with an X
- Measure out 10cm3 of sodium thiosulphate solution into a flask
- Add 40 cm3 of distilled water into the solution
- Warm the solution gently to about 25°C
- Add 5 of hydrochloric acid
- Note the temperature and the time
- Swirl the contents of the flask and place the flask over the X on the paper
- Observe the X by looking down vertically through the solution
- Take note of the time it takes for the X to “disappear” i.e. the time it takes for the X to be invisible when viewed through the solution
- Rinse the flask and repeat the experiment by heating the sodium thiosulphate solution to 30°C,40°C, 50°C and 60°C respectively before adding the acid
- Tabulate the results
- Plot the results onto a graph
Observations and results

Rate of reaction and temperature. Image credit bbc
- The higher the temperature of the sodium thiosulphate solution the faster the reaction
- At some point the rate of reaction stops increasing even though the temperature is increased
- This is because at this temperature the particles of the reagents would be colliding at a maximum possible rate i.e the reaction is almost instantaneous/as fast as it can be
Conclusion
- Increasing the temperature of a reaction/reagents results in an increase in the rate of reaction
- This is because as temperature is increased the particles of the reagents move faster and collide at a higer rate
- Also particles can overcome the reaction energy barrier at a faster rate
- This rate cannot be sped up indefinitely at a certain point the rate of reaction stops increasing even though temperature is increased
- This is known as the optimum temperature
To access more topics go to the Combined Science Notes page.
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