7. In an electrolysis cell, a constant current of 1.90 A is passed through an aqueous $CuCl_2$ solution for 15.0 min. At the end of the experiment, 0.468 g of Cu(s) is obtained as the target reduction product. What fraction of the electrons passed through the circuit was successfully used to produce Cu(s)? (A) 20.8% (B) 41.6% (C) 62.4% (D) 83.1% (E) 100%

14. In the development of the hydrogen economy, one of the most crucial challenges is safely storing hydrogen gas. For example, magnesium metal has the hcp (hexagonal close-packed) lattice structure and can use the empty space between Mg atoms (interstitial sites) to store smaller hydrogen molecules. The overall reaction can be represented as: Mg(s) + H2(g) ⇌ MgH2(s) The equilibrium pressures of hydrogen gas at different temperatures are plotted in the figure to the right. Based on these data, what are the signs of ΔH and ΔS for this reaction? (A) ΔH > 0, ΔS > 0 (B) ΔH < 0, ΔS < 0 (C) ΔH < 0, ΔS > 0 (D) ΔH > 0, ΔS < 0 (E) There is no sufficient information to determine the signs of ΔH and ΔS

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