Enthalpy of Formation and Bond Enthalpies

The enthalpyA measure of the total heat content of a system. of formation (also known as the heat of formation) is the enthalpy change that occurs when a substance is formed from its elements in their standard states. The standard state of a substance is defined as the most stable form of the substance at a pressure of 1 atmosphere and a temperature of 25 degrees Celsius.

The enthalpy of formation is an important property in thermochemistry, and it is typically given in units of energy per mole of substance. The enthalpy of formation can be used to calculate the enthalpy change of a chemical reaction, by using Hess's Law to break the reaction down into a series of intermediateAny structure in the reaction profile which is connected by two transition states and is an energy minima. Although intermediates are energetically disfavoured they are stable and can sometimes be isolated. reactions whose enthalpy changes are known or can be measured.

Bond enthalpies are a measure of the energy required to break a chemical bond, and they are typically given in units of energy per mole of bond. Bond enthalpies are an important property in thermochemistry, and they can be used to predict the enthalpy change of a chemical reaction, by using Hess's Law to break the reaction down into a series of intermediate reactions whose bond enthalpies are known or can be measured.

Bond enthalpies can be measured using a variety of techniques, including spectroscopyThe study of how matter interacts with electromagnetic radiation. Depending on what radiation is used there are different types of spectroscopy UV, NMR, IR. Note mass spectroscopy does not actually utilise electromagnetic radiation but is still referred to as spectroscopy., calorimetry, and computational chemistry. Bond enthalpies are typically used in conjunctionA word that links words, phrases, or clauses. with the enthalpy of formation to predict the enthalpy change of a chemical reaction.