Specific Heat CapacityAQA GCSE Physics: Revision notes
Section 1
Internal Energy
Energy is stored inside a system by the particles (atoms and molecules) that make it up - this is called internal energy. Internal energy is defined as the total kinetic energy and potential energy of all the particles that make up a system.
Section 2
Heating and Internal Energy
Heating a system transfers energy to its particles, which either:
- Raises the temperature of the system (particles move/vibrate faster - more kinetic energy), or
- Produces a change of state (particles gain potential energy, overcoming forces holding them together, without necessarily raising temperature)
Which of these happens depends on whether the substance is already at its melting or boiling point.
Section 3
Calculating Thermal Energy Changes
The energy needed to change the temperature of a substance is calculated using ΔE = mcΔθ (change in thermal energy in J, mass in kg, specific heat capacity c in J/kg°C, temperature change Δθ in °C).
Specific heat capacity is defined as the energy required to raise the temperature of one kilogram of a substance by one degree Celsius. Substances with a high specific heat capacity (like water) need a lot of energy to change temperature, and release a lot of energy as they cool.
Always convert mass to kilograms and temperature to °C before substituting into ΔE = mcΔθ.
Heating 3 kg of water (c = 4200 J/kg°C) by 20°C requires ΔE = 3 × 4200 × 20 = 252,000 J.
Must Know
- Internal energy = total kinetic energy + potential energy of all particles in a system
- Heating either raises temperature or causes a change of state, depending on the particles' energy
- ΔE = mcΔθ calculates the change in thermal energy stored
- Specific heat capacity = energy to raise 1 kg of a substance by 1°C
- High specific heat capacity substances (like water) resist temperature change
That's the notes covered.
Carry on to the next subtopic.