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CalorimetryOxford AQA IGCSE Chemistry: Revision notes

Section 1

What is calorimetry?

Calorimetry is the experimental technique used to measure the amount of energy transferred during a chemical reaction, usually by monitoring the temperature change of water or a solution.

Key termscalorimetry

Section 2

How is the energy released by burning a fuel measured?

Simple calorimetry to measure the energy released when a substance burns:

  1. A known mass/volume of water is placed in a glass or metal container
  2. A thermometer measures the starting temperature of the water
  3. The substance is burned underneath or near the container, heating the water
  4. The highest temperature reached is recorded, and the temperature change is calculated

The energy transferred to the water can then be calculated using Q = mcΔT.

Common mistake

Metal containers conduct heat better than glass, so more energy reaches the water — but some energy is still lost to the surroundings, meaning experimental values are usually lower than the true energy content of the fuel.

Section 3

What is the equation Q = mcΔT?

This equation calculates the energy transferred (Q) to a substance (usually water):

Q = m x c x ΔT

  • Q = energy transferred, in joules (J)
  • m = mass of the substance being heated (usually water), in grams (g)
  • c = specific heat capacity of the substance, in J/g°C
  • ΔT = change in temperature, in °C

Energy is measured in joules (J) or kilojoules (kJ) (1 kJ = 1000 J).

Key termsspecific heat capacity
Example

If 100 g of water increases in temperature by 20°C, and the specific heat capacity of water is 4.2 J/g°C, then Q = 100 x 4.2 x 20 = 8400 J = 8.4 kJ

Section 4

How is calorimetry used for reactions in solution?

For reactions that happen in solution — such as neutralisation or a solid reacting with water — the energy change is calculated from the temperature change of the solution itself, rather than heating a separate container of water:

  1. The reactants are mixed together in an insulated container (e.g. a polystyrene cup) to reduce energy loss to the surroundings
  2. The temperature of the solution is recorded before and after mixing
  3. The temperature change is used to calculate the energy transferred to or from the solution using Q = mcΔT (m is usually the mass of the solution)
Key termsinsulated container

Must Know

  • Calorimetry measures energy transfer using a temperature change
  • For burning fuels: heat water in a glass or metal container and measure the temperature rise
  • Q = mcΔT (energy = mass x specific heat capacity x temperature change)
  • Energy is measured in joules (J) or kilojoules (kJ)
  • For reactions in solution (e.g. neutralisation, solids + water), an insulated container reduces energy loss and improves accuracy
  • Some energy is always lost to the surroundings, so experimental values usually underestimate the true energy change

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