Question

# 1.      Calculate the standard free energy change at 500 K for the following reaction. Cu(s) +...

1.      Calculate the standard free energy change at 500 K for the following reaction.

Cu(s) + H2O(g) à CuO(s) + H2(g)

 ΔH˚f (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.      ΔH˚ is positive and ΔS˚ is positive

b.      ΔH˚ is positive and ΔS˚ is negative

c.       ΔH˚ is negative and ΔS˚ is positive

d.      ΔH˚ is negative and ΔS˚ is negative

e.      ΔG 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.

#### Homework Answers

Answer #1

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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