Which among the following is TRUE for isobaric process?

Which among the following is TRUE for isobaric process?
  1. $\Delta \mathrm{U}=0$
  2. $-\Delta \mathrm{U}=-\mathrm{W}$
  3. $\Delta \mathrm{U}=\mathrm{Q}$
  4. $\mathrm{Q}_{\mathrm{P}}=\Delta \mathrm{U}+\mathrm{P}_{\mathrm{ext}} \Delta \mathrm{V}$

Solution

When chemical reactions are carried out in the open containers under constant atmospheric pressure (isobaric process), $\Delta \mathrm{V} \neq 0$. $\mathrm{W}=-\mathrm{P}_{\mathrm{ext}} \Delta \mathrm{V}$ The mathematical expression of first law of thermodynamics is $\Delta \mathrm{U}=\mathrm{Q}+\mathrm{W}$. $\begin{array}{ll} \therefore & \Delta U=Q_P-P_{\text {ext }} \Delta V \\ \therefore & Q_P=\Delta U+P_{\text {ext }} \Delta V \end{array}$

Asked in: MHT CET 2023 (11 May Shift 1)

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