1. Calculate the standard free energy change at 500 K for the following reaction
ID: 501368 • Letter: 1
Question
1. Calculate the standard free energy change at 500 K for the following reaction.
Cu(s) + H2O(g) à CuO(s) + H2(g)
Hf (kJ/mol)
S (J/mol·K)
Cu(s)
0
33.3
H2O(g)
-241.8
188.7
CuO(s)
-155.2
43.5
H2(g)
0
130.6
2. When solid ammonium nitrate dissolves in water, the resulting solution becomes cold. Which is true and why?
a. H is positive and S is positive
b. H is positive and S is negative
c. H is negative and S is positive
d. H is negative and S is negative
e. G is negative independent of temperature
3. For a reaction, the value of the equilibrium constant, K, at 298 K is 5.0 x 108. The standard free energy change for this reaction is what?
4. Given the reaction P2(g) + 3Cl2(g) --> 2PCl3(g) the standard free energy change is -642.9 kJ at 298 K. If the partial pressure of phosphorus (P2) gas is 1.5 atm, chlorine gas is 1.6 atm, and phosphorus trichoride gas 0.65 atm, calculate the free energy change for the reaction.
Hf (kJ/mol)
S (J/mol·K)
Cu(s)
0
33.3
H2O(g)
-241.8
188.7
CuO(s)
-155.2
43.5
H2(g)
0
130.6
Explanation / Answer
deltaG= deltaH-TdeltaS
deltaG for Cu(s) = 0 -500k(0.0333kJ/molK) = -16.65kJ/mol (keeping the given values of delta H,T,deltaS)
deltaG for H2O(g) = -241.8kJ/mol - 500k*(0.1887J/molK) = -94.59kJ/mol
deltaG for CuO(s) = -155.2kJ/mol -500k*(0.0435kJ/molK) = -176.95kJ/mol
deltaG for H2(g) = 0 - 500K*(0.1306kJ/molK) = -65.3kJ/mol
DeltaGrxn = sum of deltaG for products - sum of deltaG for reactants
= (-176.5+(-65.3)) - (-16.65+(-94.59))
= -241.8 - (-111.24) = -130.56kJ/mol
deltaG rxn = -130.56kJ/mol
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