When a system is heated, the system gains heat energy. This heat energy is transferred to kinetic energy, so particles move with a greater speed. A more detailed explanation on the kinetic particle theory can be found here.
When a system is continuously heated, the system
i) increases temperature OR
ii) undergoes change of state
I. Increase in Temperature
When heat is added, the temperature of the matter will increase.Increase in temperature happens when the slope of heating curve is not zero.
The amount of energy needed to change temperature is based on:
i) mass of material
ii) specific heat capacity (the amount of heat per unit mass required to raise the temperature by one degree)
iii) the desired temperature change
The change in thermal energy with temperature change can be written by the following equation.
ΔQ = mcΔT
ΔQ = change in heat energy
m = mass
c = specific heat capacity
ΔT = change in temperature
For example, how much thermal energy should be added to 800 g of 25 °C water to change the temperature to 45 °C? The specific heat capacity of water is 4,200 J/kg·°C.
m = 800 g = 0.800 kg
c = 4,200 J/kg·°C
ΔT = 20°C
ΔQ = 0.800 x 4,200 x 20 = 6.7 x 104 J
II. Change of State
Matter can change from one state to another state, which is called change of state. During change of state, temperature remains constant even when heat is added to the matter. The thermal energy added to the matter is used to break the bonds between the particles during change of state.
1. solid → liquid
When heat is added to solid, temperature rises to a point when solid starts to change into liquid. The change of solid into liquid is called melting. For water, melting happens at 0°C.
2. liquid → gas
When heat is added to liquid, temperature rises to a point when liquid starts to change into gas. The change of liquid into gas is called boiling. For water, melting happens at 100°C.