Specific Heat Capacity (Cambridge O Level Physics)

• 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

• Heating a system will change the energy stored in a system by increasing the kinetic energy of its particles
  • The Kelvin temperature of the gas is related to the average kinetic energy of the molecules

• This increase in kinetic energy (and therefore energy stored in the system) can:
  • Cause the temperature of the system to increase
  • Or, produce a change of state (solid to liquid or liquid to gas)

• The internal energy of a gas is the sum of the kinetic energy of all the molecules
• The higher the temperature, the higher the average kinetic energy of the molecules and vice versa
  • This means they move faster
  • This applies to all states of matter, but the motion of particles in a solid is different to that of particles in a gas

• If the temperature of a gas is increased, the particles move faster and gain kinetic energy
  • Therefore, they will collide more with each other and the container leading to an increase in pressure

• The temperature (in Kelvin) is proportional to the average kinetic energy of the molecules

T ∝ KE

• How much the temperature of a system 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 amount of energy required to raise the temperature of 1 kg of the 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 (ie. it takes less energy to change its temperature)
  • If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature)
  
  
  

Low vs high specific heat capacity

Calculating Specific Heat Capacity

• The specific heat capacity in terms of 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)