Chemical Thermodynamics Question 365

Question: For the combustion reaction at $ 298K $

$ 2Ag( s )+1/2O_2( g )\xrightarrow{{}}2Ag_2O( s ) $ Which of the following alternatives is correct-

Options:

A) $ \Delta H=\Delta U $

B) $ \Delta H>\Delta U $

C) $ \Delta H<\Delta U $

D) $ \Delta H $ and $ \Delta U $ has no relation with each other

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Answer:

Correct Answer: C

Solution:

  • $ \Delta H=\Delta U+\Delta nRT $

$ \Delta n=n_{p}-n_{R} $ Now, $ \Delta n=2-\frac{5}{2}=-\frac{1}{2} $

$ \therefore \Delta H=\Delta U-\frac{1}{2}RT $ Thus, $ \Delta U=\Delta H+\frac{1}{2}RT $

$ \therefore \Delta U>\Delta H $



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