Electrochemistry

$\mathrm{Cu}_{(\mathrm{s})}+2 \mathrm{H}_{(\mathrm{aq})}^{+} \longrightarrow \mathrm{Cu}_{(\mathrm{aq})}^{+2}+\mathrm{H}_{2(\mathrm{~g})}$

$\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cu}_{(\mathrm{aq})}^{+2} \longrightarrow 2 \mathrm{H}_{(\mathrm{aq})}^{+}+\mathrm{Cu}_{(\mathrm{s})}$

$\mathrm{Cu}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \longrightarrow \mathrm{Cu}_{(\mathrm{aq})}^{+2}+2 \mathrm{H}_{(\mathrm{aq})}^{+}$

$\quad \mathrm{Cu}_{(\mathrm{aq})}^{+2}+2 \mathrm{H}_{(\mathrm{aq})}^{+} \longrightarrow \mathrm{Cu}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})}$