Calorimetry - IGCSE Chemistry Revision Notes

Overview

Calorimetry is a technique used to measure the amount of energy transferred in a chemical reaction. It is a crucial part of understanding the energetics of reactions, particularly in IGCSE Chemistry.

Types of Calorimetry

There are two primary types of calorimetry experiments discussed:

1. Enthalpy Changes of Reactions in Solution
2. Enthalpy Changes of Combustion

Reactions in Solution

• To calculate the energy produced by a chemical reaction in solution, we measure the temperature change when the solutions are mixed.
• The solutions are mixed in an insulated container to prevent heat loss.
• Applications include:
  • Neutralisation reactions
  • Dissolving solids in water
  • Displacement reactions

Assumptions

• Specific heat capacity of the solution is the same as pure water, i.e., 4.18 J/g/°C.
• Density of the solution is the same as pure water, i.e., 1 g/cm³.
• Specific heat capacity of the container is ignored.
• Reaction is complete with negligible heat losses.

Apparatus

• A simple calorimeter can be made using a polystyrene cup, a vacuum flask, or a metal can.

Method

1. Add a fixed volume of one reagent to the calorimeter and record the initial temperature.
2. Add an excess amount of the second reagent and stir continuously.
3. Record the maximum temperature and calculate the temperature rise.

Calculations

• The energy released is calculated using the formula:

  [ Q = m \times c \times \Delta T ]

  Where:

  • Q = heat energy change (J)
  • m = mass of the substance being heated (g)
  • c = specific heat capacity (J/g/°C)
  • ΔT = temperature change (°C)

Enthalpy of Combustion Experiments

• Uses heat released by a combustion reaction to increase the heat content of water.

Setup

• A typical simple calorimeter measures the temperature changes in water.

Method

1. Measure a fixed volume of water into a copper can.
2. Weigh the spirit burner with fuel.
3. Measure initial water temperature.
4. Burn fuel while stirring the water.
5. Extinguish the flame after a 20°C rise and record the final temperature.
6. Re-weigh the spirit burner.

Calculations

• Similar to solution reactions, using the specific heat capacity of water.

Sources of Error

• Heat losses to surroundings and calorimeter.
• Incomplete combustion.
• To reduce errors:
  • Minimize distance between flame and calorimeter.
  • Use a lid on the calorimeter.
  • Shield against draughts.

Examiner Tips

• Be able to outline the experiment and process experimental data.

These notes cover important details about calorimetry, including experimental methods, assumptions, calculations, and potential errors. Ensure you understand the principles and how to apply them in practical scenarios.