Model Paper 2 — Chemistry STD 11 Science — Question
Gujarat BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 23 Marks
Question
Give the relationship between $\Delta U$ and $\Delta H$ for gases.
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Answer
Let $V_A$ be the total volume of gaseous reactants, $V _{ B }$ be the total volume of gaseous product. Let $n _{ A }$ be the number of moles of the reactant, $n _{ B }$ be the number of moles of the product, At constant pressure and temperature, $ \begin{aligned} & p V_A=n_A R T \\ & p V_B=n_B R T \\ & \Rightarrow pV_{B}-pV_{A}=\left(n_{B}-n_{A}\right) RT \\ & \Rightarrow p \Delta V=(\Delta n)_g RT \end{aligned} $ Here, $(\Delta n)_g=n_B-n_A$ is equal to the difference between the number of moles of gaseous products and gaseous reactants. We know that, $ \Delta H=\Delta U+(\Delta n)_g R T $ Now, $\Delta H = q _{ p }$ (heat change under constant pressure), $\Delta U = q _{ v }$ (heat change under constant volume). Therefore, $q_p=q_v+(\Delta n)_g R T$
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