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Unformatted text preview: 4 H = 10 J During a chemical reaction it is often rather convenient to mea-sure the heat given o f by a reaction. In fact, you will do this in lab. If the heat is measured at constant pressure then it is simply the change in enthalpy for the reaction: 4 H = H products H reactants (21.5) If 4 H is positive that means that q P is positive and heat energy is taken in by the system. Reactions with positive 4 H are called endothermic reactions. If 4 H is negative that means that q P is negative and heat energy is given o f by the system. Reactions with negative 4 H are called exothermic reactions. REVIEW OF THE FIRST LAW, ENTHALPY, AND HESS LAW 89...
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This document was uploaded on 11/01/2011 for the course CHM 2046 at University of Florida.
- Fall '07