Specific Heat Capacity (Cambridge (CIE) IGCSE Physics)

Internal energy

• A rise in the temperature of an object increases its internal energy

  • This can be thought of as due to an increase in the average speed of the particles

  • Increasing speed increases kinetic energy

• Internal energy is defined as:

The total energy stored inside a system by the particles that make up the system due to their motion and positions

• Motion of the particles affects their kinetic energy

• Positions of the particles relative to each other affects their potential energy

  • Together, these two make up the internal energy of the system

    

    Substances have internal energy due to the motion of the particles and their positions relative to each other

Average kinetic energy

Extended tier only

• Heating a system changes a substance's internal energy by increasing the kinetic energy of its particles

  • The temperature of the material, therefore, is related to the average kinetic energy of the molecules

• An increase in temperature leads to an increase of the average kinetic energy of the particles in the substance

  • This also means that internal energy increases, as internal energy is the sum of all kinetic and potential energies

As the container heats up, the gas molecules move faster. Faster motion causes higher kinetic energy and therefore higher internal energy

Specific heat capacity

Extended tier only

What is specific heat capacity?

• When heated, a substance's temperature can increase 

• The amount by which the temperature increases depends on:

  • The mass of the substance heated

  • The type of material

  • The amount of thermal energy transferred in to the system

• The specific heat capacity, c, of a substance is defined as:

 The energy required per unit mass per unit temperature increase

• In other words, this is the amount of energy required to raise the temperature of 1 kg of a substance by 1 °C

• Different substances have different specific heat capacities

  • If a substance has a low specific heat capacity, it heats up and cools down quickly (i.e. it takes less energy to change its temperature)

  • If a substance has a high specific heat capacity, it heats up and cools down slowly (i.e. it takes more energy to change its temperature)

Low vs high specific heat capacity

Calculating specific heat capacity

• The amount of energy needed to raise the temperature of a given mass by a given amount can be calculated using the equation:

• Where:

  • ΔE = change in thermal energy, in joules (J)

  • m = mass, in kilograms (kg)

  • c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)

  • Δθ = change in temperature, in degrees Celsius (°C)