Investigating exothermic and endothermic reactions
Dr Maggie Aderin-Pocock and Dr Alex Lathbridge demonstrate how to investigate exothermic and endothermic reactions
Required practical - investigating energy changes
Aim
To investigate the variables that affect temperature changes in reacting solutionMixture formed by a solute and a solvent..
Apparatus
- Polystyrene cup.
- Thermometer.
- 250 cm3 glass beaker.
- Measuring cylinder.
- Top pan balance.
Planning the practical
You could investigate one or more chemical reactions, for example:
- acidSubstance producing more hydrogen ions than hydroxide ions when dissolved in water. reacting with metals
- acids reacting with metal carbonates
- acids reacting with alkaliSubstance producing more hydroxide ions than hydrogen ions when dissolved in water.
- displacement reactionA reaction that occurs when a more reactive element replaces a less reactive element in a compound. of metals
Hazards, risks and precautions
| Hazard | Possible harm | Possible precaution |
| Dilute acids and alkalis | May irritate the skin or eyes | Avoid contact with skin, rinse off skin if necessary, wear eye protection |
| Solutions of metal salts (used in displacement reactions) | Dangerous to the environment | Dispose of metal salt solutions as advised by teacher, some metal salts are collected for safe disposal rather than being poured down the normal drain |
| Hazard | Dilute acids and alkalis |
|---|---|
| Possible harm | May irritate the skin or eyes |
| Possible precaution | Avoid contact with skin, rinse off skin if necessary, wear eye protection |
| Hazard | Solutions of metal salts (used in displacement reactions) |
|---|---|
| Possible harm | Dangerous to the environment |
| Possible precaution | Dispose of metal salt solutions as advised by teacher, some metal salts are collected for safe disposal rather than being poured down the normal drain |
Carrying out the practical
Method one
Reacting two solutions, eg acid and alkali.
- Place the polystyrene cup inside the glass beaker to make it more stable.
- Measure an appropriate volume of each liquid, eg 25 cm3.
- Place one of the liquids in a polystyrene cup.
- Record the temperature of the solution.
- Add the second solution and record the highest or lowest temperature obtained.
- Change your independent variableThe variable which is changed during an investigation. The independent variable is normally plotted on the x axis of a graph. and repeat the experiment. Your independent variable could be the concentration of one of the reactants, or the type of acid/alkali being used, or the type of metal/metal carbonate being used.
Method two
Reacting a solid with a solution, eg metal and acid.
- Place the polystyrene cup inside the glass beaker to make it more stable.
- Measure an appropriate volume of the solution, eg 25 cm3.
- Measure an appropriate mass of the solid, or select a suitable sized piece of metal.
- Place the solution in a polystyrene cup.
- Record the temperature of the solution.
- Add the solid and record the highest or lowest temperature obtained.
- Change your independent variable and repeat the experiment. Your independent variable could be the surface area of the solid, or the type of acid being used, or the type of metal being used.
Analysis
The bigger the temperature change in the reaction, the more energy is absorbed or released. Remember that endothermicReaction in which energy is taken in. reactions absorb energy from the surroundings, and exothermicReaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases. reactions transfer heat into the surroundings.
Evaluation
The biggest source of error in this experiment is unwanted heat transfer. Using a lid can help to reduce this.
More guides on this topic
- Motion - AQA Synergy
- Newton's laws - AQA Synergy
- Circuits - AQA Synergy
- Mains electricity - AQA Synergy
- Rates of reaction - AQA Synergy
- Energy, rates and reactions - AQA Synergy
- Equilibria - AQA Synergy
- Electrons and chemical reactions - AQA Synergy
- Sample exam questions - movement and interactions - AQA Synergy
