Medium Practice — Set 1

Quick Recap — First-Law & Enthalpy Calculations

• $\Delta U=q+w$; for expansion against constant $P_{ext}$: $w=-P_{ext}\Delta V$.
• $\Delta H=\Delta U+\Delta n_g RT$ (use $R=8.314$ J/mol$\cdot$K).
• Hess's law: add/subtract given equations (and their $\Delta H$).
• Bond-enthalpy method: $\Delta H=\sum(\text{bonds broken})-\sum(\text{bonds formed})$. Isothermal ideal gas: $\Delta U=0$, so $q=-w$.