Question

$E_{Cu/C{u}^{++}}^{\circ }=-0.34$ V, $E_{Cr/C{r}^{+++}}^{\circ }=0.74$ V, $E_{Pb/P{b}^{++}}^{\circ }=0.126$ V
Predict correct set of spontaneous reactions from the following:

• A. $3Pb+2C{r}^{+++}\to 3P{b}^{++}+2Cr$
  $Cu+2HCl\to CuC{l}_2+H_2$
• B. $2Cr+3P{b}^{++}\to 2C{r}^{+++}+3Pb$
  $Cu+2HCl\to CuC{l}_2+H_2$
• C. $2Cr+3C{u}^{++}\to 2C{r}^{+++}+3Cu$
  $Pb+C{u}^{++}\to P{b}^{++}+Cu$
• D. $3Pb+2C{r}^{+++}\to 3P{b}^{++}+2Cr$
  $Cu+P{b}^{++}\to C{u}^{++}+Pb$

Answer 1

Answer: (A)

$3Pb+2C{r}^{+++}\to 3P{b}^{++}+2Cr$

$Cu+2HCl\to CuC{l}_2+H_2$
For spontaneous reaction $E_0^{cell}$ $>zero$

$E_{cell}^0=$ $(E_{Cr/{Cr}^{3+}}^0+E_{{Pb}^{2+}/Pb}^0)$$=(0.74-0.126)>zero$

$E_{cell}^0=$ $(E_{Cu/{Cu}^{2+}}^0+E_{H^{+}/H_2}^0)=$ $-0.34<zero$

$E_{cell}^0=$ $(E_{Pb/{Pb}^{2+}}^0+E_{{Cu}^{+}/Cu}^0)$ $=(0.34+0.126)>zero$

$E_{cell}^0=$$(E_{Cr/{Cr}^{3+}}^0+E_{{Cu}^{2+}/Cu}^0)$ $=(0.74+0.34)>zero$