Question 16.7: Graded When zinc is dissolved in a strong acid, zinc ions an...
GRADED
When zinc is dissolved in a strong acid, zinc ions and hydrogen gas are produced.
Zn(s) + 2H^{+}(aq) → Zn^{2+}(aq) + H_{2}(g)
At 25°C, calculate
ⓐ ΔG°.
ⓑ ΔG when P_{H_{2}} = 750 mm Hg, [Zn^{2+}] = 0.10 M, [H^{+}] = 1.0 × 10^{-4} M.
ⓒ the pH when ΔG = -100.0 kJ, P_{H_{2}} = 0.933 atm, [Zn^{2+}] = 0.220 M and the mass of Zn is 155 g.
ⓐ
| ANALYSIS | |
| equation for the reaction (Zn(s) + 2H^{+}(aq) → Zn^{2+}(aq) + H_{2}(g))
T(25°C) |
Information given: |
| ΔG_{f}° values at 25°C (Appendix 1) | Information implied |
| ΔG° | Asked for |
STRATEGY
1. Find ΔG° by substituting ΔG_{f}° values into Equation 16.3.
ΔG°_{reaction} = ΣΔG°_{f_{ products}} – ΣΔG°_{f_{ reactants}} (16.3)
2. Recall that ΔG_{f}° for elements in their native state at 25°C and H^{+}(aq) is zero.
ⓑ
| ANALYSIS | |
| P_{H_{2}} (750 mm Hg); [Zn^{2+}](0.10 M); [H^{+}] (1.0 × 10^{-4} M); T(25°C) from part (a): ΔG°(-147.1 kJ) | Information given: |
| R value in energy units | Information implied |
| ΔG | Asked for |
STRATEGY
ⓒ
| ANALYSIS | |
| P_{H_{2}}(0.933 atm); [Zn^{2+}](0.220 M); mass Zn(155 g); T(25°C) ΔG(-100.0 kJ) From part (a): ΔG°(-147.1 kJ) |
Information given: |
| R value in energy units | Information implied |
| pH | Asked for |
STRATEGY
1. Find Q by substituting into Equation 16.4.
ΔG = ΔG° + RT ln Q (16.4)
2. Write the equation for Q.
3. Solve for [H^{+}] by substituting into the Q expression. Change [H^{+}] into pH.
