Chemistry: This Day in Science History - August 7 - Germain Hess

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This Day in Science History - August 7 - Germain Hess Aug 6th 2011, 22:05 August 7th is Germain Henri Hess's birthday. Hess was the German chemist that determined the energy formed by a chemical reaction is independent of the steps to complete the reaction. This is known in thermodynamics as Hess's Law. Hess's Law states the total enthalpy or energy change of a reaction is independent of the reaction pathway. If a reaction takes many steps to complete, the total change in enthalpy is equal to sum of the enthalpy changes for each individual step. When doing Hess's Law homework problems, there are three rules to follow: 1. Arrange the given equations so the reactants and products are on the appropriate sides of the arrows. 2. If you reverse a reaction, you must reverse the sign of Î"H 3. If you multiply a reaction by a constant to obtain the correct coefficient, you must multiply Î"H by the same constant. It is also helpful to work the reaction backwards from the end of the reaction. It is also useful to see completed enthalpy change example problems to understand the steps needed to complete the homework problem. Find out what else occurred on this day in science history.

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