Measuring temperature change (Edexcel GCSE Chemistry Combined Science): Revision Notes
📚 Revision Notes
Measuring temperature change
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In this experiment, you will measure the temperature change when two substances (reagents) react. The temperature change helps you understand whether the reaction is endothermic (takes in heat, so temperature decreases) or exothermic (gives out heat, so temperature increases).
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Steps for Measuring Temperature Change
- Set up an insulated container:
- Place a polystyrene cup inside a large beaker filled with cotton wool. This provides insulation to limit energy transfer to or from the reaction mixture.
- Add the first reagent:
- Pour a known volume of the first reagent (liquid) into the polystyrene cup.
- Measure the starting temperature:
- Use a thermometer to record the initial temperature of the solution.
- Add the second reagent and stir:
- Add a measured amount of the second reagent (either a liquid or a solid). Stir the mixture to make sure the reaction happens evenly.
- Cover the cup:
- Place a lid on the cup to reduce energy loss through evaporation.
- Record temperature changes:
- Watch the thermometer and note the highest or lowest temperature the mixture reaches.
- Calculate the temperature change:
- Subtract the starting temperature from the highest or lowest temperature to find the temperature change.
Examples of Reactions that Cause Temperature Changes
| Type of Reaction | What Happens |
|---|---|
| Dissolving salts in water | Add salt to water and measure the temperature change as the salt dissolves. |
| • Ammonium chloride: Dissolving it lowers the temperature (endothermic). | |
| • Calcium chloride: Dissolving it raises the temperature (exothermic). | |
| Neutralisation reactions | When an acid and a base react to form salt and water, most reactions are exothermic (release heat). |
| • Exception: Ethanoic acid and sodium carbonate are endothermic. | |
| Displacement reactions | A more reactive metal displaces a less reactive metal from its compound. These reactions are exothermic. |
| • Example: Zinc powder + copper sulfate (heat is released). | |
| Precipitation reactions | When two solutions are mixed and an insoluble solid (precipitate) forms, these reactions are usually exothermic. |
| • Example: Lead (II) nitrate + potassium iodide. |
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Key Points
- Endothermic reactions absorb heat, so the temperature of the mixture decreases.
- Exothermic reactions release heat, so the temperature of the mixture increases.