Heating and changes of state

• Energy is stored inside a system by the particles (atoms and molecules) that make up the system. This is called internal energy.
• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of the substance
• The increase in temperature of a system depends on the mass of the substance heated, the type of material and the energy input.
• change in thermal energy = mass ×specific heat capacity × temperature change
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
• The energy needed for a substance to change state is called latent heat. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature.
• Specific latent heat of fusion – change of state from solid to liquid.
• Specific latent heat of vaporisation – change of state from liquid to vapour.