ThermochemistryHard
Question
Ethyl chloride is prepared by the reaction of ethylene with hydrogen chloride as
C2H4(g) + HCl(g) → C2H5Cl(g): ΔH = −72.3 kJ
What is the value of ΔU (in kJ) if 70 g of ethylene and 73 g of HCl are allowed to react at 25°C?
Options
A.−69.8
B.−180.75
C.−174.5
D.−139.6
Solution
For the reaction:
$\Delta U = \Delta H - \Delta n_{g}RT = ( - 72.3) - ( - 1) \times \frac{8.314}{1000} \times 298 = - 69.8\text{ kJ}$
As HCl is limiting reagent, for the given amount, $\Delta U = 2 \times ( - 69.8) = - 139.6\text{ kJ}$
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