physics aqa specific latent heat

what does changing the internal energy do

Changing the internal energy of a material will cause it to change temperature or change state:

what is specific heat capcaity

he energy required for a particular change in temperature

specific latent heat

the energy required for a particular change in state

As there are two boundaries, solid/liquid and liquid/gas, each material has two specific latent heats:

• latent heat of fusion - the amount of energy needed to melt orfreeze the material at its melting point

• latent heat of vaporisation - the amount of energy needed to boil or condense the material at its boiling point

what is specific latent heat

Specific latent heat is the amount of energy required to change the state of 1 kilogram (kg) of a material without changing its temperature.

The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:

change in thermal energy = mass × specific latent heat

ΔE_t =m x l 

• mass (m) is measured in kilograms (kg)

• specific latent heat (l) is measured in joules per kilogram (J/kg)

• change in thermal energy (ΔE_t) is measured in joules (J)

Measuring latent heat

Latent heat can be measured from a heating or cooling curve line graph. If a heater of known power is used, such as a 60 W immersion heater that provides 60 J/s, the temperature of a known mass of ice can be monitored each second. This will generate a graph that looks like this.

the horizontal line meaning

The graph is horizontal at two places. These are the places where the energy is not being used to increase the speed of the particles, increasing temperature, but is being used to break the bonds between the particles to change the state.The longer the horizontal line, the more energy has been used to cause the change of state. The amount of energy represented by these horizontal lines is equal to the latent heat.