3.1.6Physical Chemistry
Practical- Investigating Temperature Changes
5 min read 5 parts Lesson 8 of 19 Unit quiz
Section 1 of 5Method
The same simple calorimeter is used for each process, with only the chemicals changed.
1
Place a fixed volume of the first solution into an insulated container with a lid, and measure its initial temperature.
2
Add the measured amount of the second substance, such as a fixed mass of iron powder or ammonium nitrate, and stir continuously.
3
Record the highest temperature reached for a rise, or the lowest temperature reached for a fall.
4
Calculate the temperature change and classify the process: a rise is exothermic and a fall is endothermic.
Section 2 of 5Example Processes
Three processes are commonly investigated with this method.
Neutralisation
- Hydrochloric acid added to sodium hydroxide in the calorimeter gives a temperature rise, showing an exothermic reaction.
Displacement
- Iron added to copper(II) sulfate solution gives a temperature rise, because a displacement reaction releases energy.
Dissolving
- Ammonium nitrate dissolving in water gives a temperature fall, showing that the process is endothermic.
Control
- Only the chemicals being investigated should change between runs, so that the results can be compared fairly.
| Process | Expected temperature change | Classification |
|---|---|---|
| Neutralisation of HCl and NaOH | Rise | Exothermic |
| Iron and copper(II) sulfate | Rise | Exothermic |
| Ammonium nitrate dissolving | Fall | Endothermic |
Section 3 of 5Improving the Investigation
Improving the Investigation
Lid
- A lid reduces heat transfer to the surroundings and gives a more accurate maximum or minimum temperature.
Same volumes
- Using the same volume and concentration of solution allows fair comparison between processes.
Stirring
- Continuous stirring makes sure the temperature is uniform throughout the solution.
Initial reading
- Measuring the initial temperature before mixing gives the baseline for the temperature change.
Section 4 of 5Worked Example
Question
- In an investigation, 25.0 cm³ of water in a calorimeter has an initial temperature of 21.0 °C.
- Ammonium nitrate is added and the lowest temperature reached is 16.5 °C.
- Calculate the temperature change and classify the process.
- Temperature change ΔT = final − initial = 16.5 − 21.0 = −4.5 °C.
- The temperature fell, so heat was taken in from the surroundings.
- A fall in temperature shows an endothermic process.
Answer
- ΔT = −4.5 °C.
- Dissolving ammonium nitrate is endothermic.
Section 5 of 5Exam Checklist & Tips
3.1.6 – Key Points for the Exam
- Simple calorimeter An insulated container with a lid, used to measure temperature changes.
- Exothermic A process that releases heat energy and causes a temperature rise.
- Endothermic A process that takes in heat energy and causes a temperature fall.
- Control variable A factor kept the same to make a fair comparison between experiments.
Common Mistakes
- Recording the temperature of the chemicals after the reaction is complete, rather than the highest or lowest value reached.
- Classifying a temperature fall as exothermic; a fall means the process is endothermic.
- Changing the volumes or concentrations between processes, which makes the comparison unfair.
- Omitting the lid, which allows heat to be lost and gives a smaller temperature change.