Chapter5_2 - Mary J. Bojan Chem 110 Chemical Reactions When...

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Unformatted text preview: Mary J. Bojan Chem 110 Chemical Reactions When natural gas burns: CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(l) Reaction produces heat and light Is energy conserved? What are the signs of q and w for the overall reaction? Where does the energy come from? Is energy stored or released when bonds are broken? Mary J. Bojan Chem 110 Relationship between Energy ( E) and Enthalpy ( H) H = Enthalpy Energy transferred when P is constant (=q p ) = H For many chemical processes, P V is small and E H Like E, H is a state function Energy transferred when V is constant = E Usually run chemical reactions at constant pressure (atmospheric). E = q + w P V = work done on system at constant P arises from expansion or contraction of the system: V = volume change of system E = q p P V P = constant q p = E + P V H Mary J. Bojan Chem 110 Thermochemical Equations A balanced chemical equation that also includes the energy change H 2 (g) + 1/2 O 2 (g) H 2 O(g) H = 241.8kJ H = enthalpy: heat given off or absorbed in the reaction 1. Enthalpy is an extensive property. 2. H for a reaction is equal in magnitude and opposite in sign to H for the reverse reaction. 3. H for a reaction depends on the states of reactants and products (gas, liquid, solid). ENTHALPY Mary J. Bojan Chem 110 ENTHALPY OF REACTION H = H(products) H(reactants) If H<0 ( ) exothermic (heat released) If H>0 (+) endothermic (heat absorbed) Mary J. Bojan Chem 110 5.1 Is this reaction 1 exothermic 2 endothermic 5.2 How much heat is given off per mole of H...
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This note was uploaded on 04/16/2009 for the course CHEM 110 taught by Professor Hofmann,brucerob during the Fall '08 term at Pennsylvania State University, University Park.

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Chapter5_2 - Mary J. Bojan Chem 110 Chemical Reactions When...

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