University of Texas, Arlington

CHEM 1442

Chapter 17 Questions

1)Which of the following is necessary and sufficient to assure that a process is spontaneous? (a) H < 0

(b) S > 0 (c) G < 0 (d) S <0 (e) none

2. The enthalpy change for the following is –891 kJ: CH₄ + 2 O₂ ? CO₂ + 2 H₂O

What is the enthalpy change associated with the complete combustion of 1.00 g of CH₄?

3. In which case will a reaction be spontaneous only at high temperature? (a) H = -

S = + (b) H = - , S = - (c) H = + , S = + (d) H = +, S = -

4. Given the reactions: (1) 2 Fe₂O₃(s) ? 4 Fe (s) + 3 O₂(g)

(2) Ag⁺ (aq) + Cl^- (aq) ? AgCl (s)

(3) H₂O (g) ? H₂O(l) In which reactions does the entropy decrease?

5. Given the reaction: CaO(s) + SO₃(g) ? CaSO₄(s) for which H = -403.l3 kJ        and S

= -189.3 J/mole.K. What is the value of G in kJ/mole at 0^oC?

6. For the reaction in equilibrium at 298 K: CaSO₄(s) + CO₂(g) ↔ CaCO₃(s) +                                     SO₃(g). If G = 217 kJ/mol , what is the value of K?

7. 2 NH₃(g) + 7/2 O₂(g) ? 2 NO₂(g) + 3 H₂O(g). The following values for S_f are: NH₃ = 192.5 J/Kmol, O₂ = 205 J/Kmol ,NO₂ = 240.4 J/Kmol, H₂O = 188.7 J/Kmol. What is S for the reaction?

Chapter 17 Useful information

?H_reaction = ∑ H _products - ∑ H _reactants ( Also works for S and G)

?G = ? H - T?S                        ?G = -RT lnK ( R = 8.314 J/mol.K)