Using enthalpies of formation (below), calculate delta H for the following react

Question

Using enthalpies of formation (below), calculate delta H for the following reaction at 25 degrees. Also calculate delta S for this reaction from standard entropies at 25 degrees. Use these values to calculate delta G for the reaction at this temperature. (ii) Using standard free energies to calculate delta G for the reaction at this temperature (double check your answers)

a) Pb(s) + 1/2O2(g) ---> PbO(s)

b) C2H4(g) + 3O2(g) -----> 2CO2(g) + 2H20(g)

%u2206H %u2206G s PB (s) 0 0 64.8 1/2O2 0 0 102.5 PBO -217.3 187.9 68.7 C2H4 52.3 68.1 219.5 O2 0 0 205 CO2 -393.5 -394.4 213.6 H2O -241.8 -228.6 188.7

Explanation / Answer

a) Pb(s) + 1/2O2(g) ---> PbO(s)

delta H = -217.3-0-0 = -217.3

delta S = 68.7-102.5-64.8 = -98.6

delta G = delta H-(Tdelta S) = -217.3 -(298*-98.6/1000) = -187.9172

delta G (from values) = -187.9 (so the same)

b) C2H4(g) + 3O2(g) -----> 2CO2(g) + 2H20(g)

delta H =2(-393.5)+2(-241.8) -52.3-3(0) = -1322.9

delta S = 2(213.6)+2(188.7)-219.5-3(205)= -29.9

delta G = delta H-(Tdelta S) = -1322.9 -(298*-29.9/1000) = -1313.989

delta G (from values) = 2(-394.4)+2(-228.6)-68.1-3(0) = -1314 (so the same)

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