Question

When a substance is heated its volume increases, give reason

Answer 1

When a solid is heated, its atoms vibrate faster about their fixed points. The relative increase in the size of solids when heated is therefore small. Metal railway tracks have small gaps so that when the sun heats them, the tracks expand into these gaps and don’t buckle.

Liquids expand for the same reason, but because the bonds between separate molecules are usually less tight they expand more than solids. This is the principle behind liquid-in-glass thermometers. An increase in temperature results in the expansion of the liquid which means it rises up the glass.

Molecules within gases are further apart and weakly attracted to each other. Heat causes the molecules to move faster, (heat energy is converted to kinetic energy) which means that the volume of a gas increases more than the volume of a solid or liquid.

However, gases that are contained in a fixed volume cannot expand - and so increases in temperature result in increases in pressure

Answer 2

Molecules within gases are further apart and weakly attracted to each other. Heat causes the molecules to move faster(heat energy is converted to kinetic energy)which means that the volume of a gas increases more that the volume of a solid or liquid.