Question

$Z{n}_{\left(s\right)}+C{u}_{\left(aq\right)}^{2+}\to C{u}_{\left(s\right)}+Z{n}_{\left(aq\right)}^{2+}$

Given that ${\Delta }_f{G}^{\circ }$ for $C{u}_{\left(aq\right)}^{2+}$ and$Z{n}_{\left(aq\right)}^{2+}$ are 65 kJ mol${}^{-1}$ and 147.2 kJ mol ${}^{-1}$ respectively, then the standard gibbs energy change for the above reaction is:

• A. $266.2kJmo{l}^{-1}$
• B. $111.2kJmo{l}^{-1}$
• C. $82.2kJmo{l}^{-1}$
• D. $-122.2kJmo{l}^{-1}$

Answer 1

Answer: (C)

$82.2kJmo{l}^{-1}$

${\Delta }_{f}G$ (reaction) $={\Delta }_{f}G\left(Cu\right(s\left)\right)+{\Delta }_{f}G\left(Z{n}^{2+}\right(aq\left)\right)-{\Delta }_{f}G\left(Zn\right(s\left)\right)-{\Delta }_{f}G\left(C{u}^{2+}\right(aq\left)\right)$

${\Delta }_{f}G$ (reaction) $=147.2-65$ kJ mol${}^{-1}$

${\Delta }_{f}G=$ 82.2 kJ mol${}^{-1}$

${\Delta }_{f}G$ for Cu(s) and Zn(s) $=$ 0 as they are in their standard states.