Explain what is meant by Enthalpy

In nature, when 2 elements react, energy is taken in to break bonds and energy is given out to form new bonds. The net change in heat energy during a reaction at constant pressure is called the enthalpy change. Enthalpy is denoted by 'delta' H, whereby the symbol delta denotes the difference in energy taken to break bonds and energy taken to make bonds.When system, gives out heat energy to the surroundings, enthalpy is lost by the system. So delta H is negative (exothermic)When system, gives out heat energy to the surroundings, enthalpy is gained by the system. So delta H is positive (endothermic).