Chemistry: The Central Science (13th Edition)

Published by Prentice Hall
ISBN 10: 0321910419
ISBN 13: 978-0-32191-041-7

Chapter 20 - Electrochemistry - Exercises - Page 903: 20.59

Answer

Step 3: Plug answers in the first equation... $$ \begin{aligned} W_{\text {max }} & =-n F E \\ & =-(1.26)(96485)(0.672 \mathrm{~V}) \\ & =-8.19 \times 10^{4} \mathrm{~J} \end{aligned} $$ Step 4: Convert work energy per mole... $$ \begin{aligned} & =\left(-8.19 \times 10^{4} \mathrm{~J}\right) /(0.631 \mathrm{~mol} \text { of } \mathrm{Sn}) \\ & =-129675 \mathrm{~J} / \mathrm{mol} \text { of } \mathrm{Sn}=-130 \mathrm{KJ} / \mathrm{mol} \text { of } \mathrm{Sn} \end{aligned} $$

Work Step by Step

$W_{\text {max }}=-n F E$ $n=$ mol of $e^{-}$ $F=96485$ Step 1: $\operatorname{Sn}(s) \rightarrow \operatorname{Sn}^{+2}(a q)+2 e^{-} \quad E_{\text {red }}=-0.136 \mathrm{~V}$ $$ I_{2}(s)+2 e^{-} \rightarrow 2 I^{-}(a q) \quad E_{\text {red }}=+0.536 \mathrm{~V} $$ $E_{\text {Cell }}=E_{\text {red }}($ cathode $/$ reduced $)-E_{\text {red }}($ Anode $/$ Oxidized $)=0.536 \mathrm{~V}-(-0.136 \mathrm{~V})=0.672 \mathrm{~V}$ Step 2: find $\mathrm{n}$ given that $75 \mathrm{~g}$ of $\mathrm{Sn}$ has been consumed. $$ \begin{aligned} & \frac{75 \mathrm{~g}}{118.71 \mathrm{~g} / \mathrm{mol}}=\frac{\text { mass }}{\text { molar mass }}=\text { moles of } \mathrm{Sn}=0.631 \\ & 0.631 \mathrm{~mol} \text { of } \mathrm{S} n \times \frac{2 \text { mol of } e^{-}}{1 \text { mol of } \mathrm{S} n}=1.26=n \end{aligned} $$ Step 3: Plug answers in the first equation... $$ \begin{aligned} W_{\text {max }} & =-n F E \\ & =-(1.26)(96485)(0.672 \mathrm{~V}) \\ & =-8.19 \times 10^{4} \mathrm{~J} \end{aligned} $$ Step 4: Convert work energy per mole... $$ \begin{aligned} & =\left(-8.19 \times 10^{4} \mathrm{~J}\right) /(0.631 \mathrm{~mol} \text { of } \mathrm{Sn}) \\ & =-129675 \mathrm{~J} / \mathrm{mol} \text { of } \mathrm{Sn}=-130 \mathrm{KJ} / \mathrm{mol} \text { of } \mathrm{Sn} \end{aligned} $$
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