CH131_12C_13A

CH131_12C_13A - o H rxn n prod o H f (products) m react o H...

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H rxn o = n D H f o ( products ) - prod m D H f o ( reactants ) react Where n, m are the stoichiometric coefficients in the balanced chemical reaction For example. .It is found that H for the following reaction carried out at standard state conditions (P = 1 atm, T = 25 o C) is 178.1 KJ CaCO 3 (s) CaO(s) + CO 2 (g) Find H f o (CaCO 3 (s)). Given: H f o (CO 2 (g)) = –393.5 KJ/mol H f o (CaO(s)) = –638.5 KJ/mol H rxn o = H f o (CaO(s)) + H f o (CO 2 (g)) – H f o (CaCO 3 (s)) all m,n =1 Rearrange H f o (CaCO 3 (s)) = H f o (CaO(s)) + H f o (CO 2 (g)) – H rxn o = –638.5 KJ –393.5 KJ – 178.1 KJ = – 1207.1 KJ
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Some final thermodynamic definitions: Reversible process => one that is infinitely close to equilibrium throughout P gas P ext e.g. gas in a cylinder with a moveable piston As piston moves (infinitely) slowly up, say, system pressure (P gas ) always equal to P ext In contrast, imagine pulling piston up quickly; P gas suddenly drops and nonuniform bec. V inc. rapidly and then P gas equilibrates w/ P ext - a very different path then the reversible one! In a reversible process, system is always very close to equilibrium: (P gas = P ext )
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Isothermal process =>
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CH131_12C_13A - o H rxn n prod o H f (products) m react o H...

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