# Chapter 18 - Exercises and Problems: 59

$57KJ$

#### Work Step by Step

We know that the change of internal energy is given as: $\Delta U=nC_v\Delta T$ We plug in the known values to obtain: $\Delta U=(21)(\frac{3}{2})(8.314)(160)$ $\Delta U=42KJ$ Now we can find the required work done as $W=Q-\Delta U$ We plug in the known values to obtain: $W=-15-42=-57KJ$

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