Burning what produces heat

Think of a burning match, or a fire in the fireplace or a roaring campfire. In each case you have felt the heat given off as these materials burn (but hopefully not as a close encounter!). Where does this heat (energy) come from?

The reactants, such as the wood in the campfire, have a certain amount of energy stored in their chemical bonds. This energy can be released when these materials react with the oxygen in the air (combustion) and are converted to the combustion products (usually carbon dioxide and water). Chemists use a quantity called the  heat of formation  as a measure of the energy stored in these compounds. The energy change associated with a combustion reaction is the difference between the energy (heat of formation) of the products and the energy (heat of formation) of the reactants.

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.