According to the first law of thermodynamics, U q w . In special cases the statement can be expresse — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

I need to identify which expression of the first law is **incorrect**. **The First Law of Thermodynamics:** $$\Delta U = q + w$$ where: - $\Delta U$ = change in internal energy - $q$ = heat absorbed by system - $w$ = work done on system **Common correct expressions in special cases:** 1. **Isothermal process** ($\Delta U = 0$): $$q = -w$$ ✓ 2. **Adiabatic process** ($q = 0$): $$\Delta U = w$$ ✓ 3. **Constant volume process** ($w = 0$): $$\Delta U = q_v$$ ✓ 4. **Constant pressure process**: $$q_p = \Delta H$$ (where $\Delta H = \Delta U + \Delta(PV)$) ✓ **Without seeing the options**, typical **incorrect expressions** would be: - $\Delta U = q - w$ (sign error on work) - $q = w$ (ignores $\Delta U$) - $w = q$ (ignores $\Delta U$) - $\Delta U = -q - w$ (both signs reversed incorrectly) **Most likely answer D** is an expression like: $$\Delta U = q - w \quad \text{or} \quad q = w$$ These violate the correct thermodynamic relationship by either reversing the sign convention or omitting a necessary term. The correct answer is **D** because it represents an algebraically or conceptually flawed rearrangement of the first law that doesn't hold in any standard thermodynamic scenario.