What is Thermochemistry?
'''Thermochemistry''' is the study of the [[energy]] and [[heat]] to do with [[chemical reaction]]s and physical transformations (physical changes). Physical transformations are when a [[state of matter]] (a [[solid]] or [[liquid]], for example) changes to another state. Examples of transformations include [[melting]] (when a solid becomes a liquid) and [[boiling]] (when a liquid becomes a [[gas]]). A reaction gives out or takes in energy. A physical transformation also gives out or takes in energy. Thermochemistry looks at these energy changes, particularly on a [[system]]'s energy exchange with its [[surroundings]]. Thermochemistry is useful in [[predict|predicting]] reactant and product quantities at all times during a given reaction. Thermochemists do this by using data, including [[entropy]] determinations. Thermochemists will tell if a reaction is [[Spontaneity (chemistry)|spontaneous or non-spontaneous]], favorable or unfavorable. [[Endothermic reaction]]s take in heat. [[Exothermic reaction]]s give out heat. Thermochemistry combines the concepts of [[thermodynamics]] with the idea of energy in the form of [[chemical bond]]s. It includes calculations of such quantities as [[heat capacity]], [[heat of combustion]], [[heat of formation]], [[enthalpy]], [[entropy]], [[thermodynamic potential|free energy]], and [[calorie]]s. [[Image:Ice-calorimeter.jpg|250px|right|thumb|The world’s first ice-calorimeter, used in the winter of 1782-83, by [[Antoine Lavoisier]] and [[Pierre-Simon Laplace]]. It was used to find the [[heat]] evolved in various [[chemical change]]s. These calculations were based on [[Joseph Black]]’s earlier discovery of [[latent heat]]. These experiments started thermochemistry.]] ==History== Thermochemistry started with two ideas:<ref>{{cite book | last=Perrot| first=Pierre | title=A to Z of Thermodynamics | publisher=Oxford University Press | year=1998 | isbn= 9780198565529|edition=First}}</ref> #Lavoisier and Laplace’s law (1780): The energy change for any transformation is equal and o