Enthalpy Characteristics

# Enthalpy Characteristics - EnthalpyCharacteristics

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Enthalpy Characteristics Because enthalpy is a state function we can always write for a chemical reaction that H = H Δ products  - H reactants Some other characteristics of enthalpy are. .. 1. If the reaction is reversed then the sign of  H Δ  is also reversed. For example, for  the reaction CH 4 (g)  + 2 O 2 (g)    CO 2 (g)  + 2 H 2 O (g) the  H Δ  is -802 kJ, that is, it is  exothermic . In contrast, the reverse reaction CO 2 (g)  + 2 H 2 O (g)    CH 4 (g)  + 2 H 2 O (g) has a  H Δ  of +802 kJ, that is, it is now  endothermic . 2. H Δ  is extensive. If the coefficients in a balanced reaction are multiplied by an  integer, then the value of  H Δ  is multiplied by the same integer. For example, Xe (g)  + 2 F 2 (g)    XeF 4 (g)        H = -251 kJ. Δ but. .. 2 Xe (g)  + 4 F 2 (g)    2 XeF 4 (s)       H = -502 kJ. Δ Hess' Law Since enthalpy is a state function, the change in enthalpy in going from some initial state  to some final state is independent of the pathway. This leads us to Hess' Law. .. Hess' Law

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In going from a particular set of reactants to a particular set of products, the  change in enthalpy is the same whether the reaction takes place in one step or in  a series of steps. For example, consider the following reaction
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## This note was uploaded on 11/22/2011 for the course CHEMISTRY CHM1025 taught by Professor Laurachoudry during the Fall '10 term at Broward College.

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Enthalpy Characteristics - EnthalpyCharacteristics

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