ABSTRACT

This chapter explains the principles of determination of heats accompanying some kinds of chemical reactions. There exist many tables of heats of reactions. They have been established by starting from standard enthalpies of formation of various compounds from their elements in their reference states. By convention, the standard formation enthalpies of elements are null in their reference states, whatever the temperature is. The adjective standard means that reactants and products are in their standard states. Organic compounds, by definition, contain carbon and hydrogen. They burn in dioxygen to yield carbon dioxide and liquid water, even when their molecules already contain oxygen atoms. Phase changes are accompanied by changes in enthalpies. They were called formerly latent heats. It is pertinent now to consider procedures permitting to determine the heat of reaction at constant temperature at one temperature different from that obtained for the same reaction at another one.