list the important effect of heat

(i) When heat is supplied to a body its temperature rises: When a material body, solid, liquid or gas, is given heat energy, its temperature increases. When this hot body gives out heat energy its temperature decreases.

(ii) Heat energy may bring about chemical changes in a substance:  When we heat substances, the heat energy breaks the original bonds between the elements and new products with new bonds are formed. For example, if marble (calcium carbonate) is heated, it turns into calcium oxide and carbon dioxide. 
(iii) A body may catch fire if it is sufficiently heated and if it is flammable. The burning of substances in air or oxygen on heating, with the release of large amount of heat energy and light energy is called combustion. Substances that burn easily in air are called flammable or combustible substances, e.g., wood, coal, petrol, etc. Substances that do not burn easily in air are called incombustible substances, e.g., glass, stone, metals, etc. 
(iv) On heating, change of state may occur, i.e. a solid may change into a liquid and a liquid may change into a gas. For example if ice (solid)  is heated it changes its state to water (liquid) and if this water is further heated it becomes water vapour (gas). Conversely when a gas loses heat energy it changes into a liquid and on further cooling it freezes into a solid.
(v) When heat is supplied to a body it expands, i.e. its dimensions are changed. Material bodies expand on heating and contract on cooling. The process due to which a material in a given state of matter expands on the absorption of heat enegy is known as thermal expansion.