4.10 understand that chemical reactions in which heat energy is given out are described as exothermic and those in which heat energy is taken in are endothermic

NOTE: before you get your head round endothermic and exothermic, it might be a good idea to understand that energy is given out when bonds are made, and taken in when bonds are destroyed...


If a reaction gives out heat, it is said to be exothermic and the energy released in bond formation is greater than the energy used in breaking bonds.

Definition for exams: An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.


If a reaction is endothermic, it takes in heat from its surroundings during the reaction process. This is because the energy required to break old bonds is greater than the energy released when new bonds are formed.

Definition for exams: An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature.