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

# Solution: First Law of Thermodynamics - Incorrect Expression ## Recall the First Law $$\Delta U = q + w$$ where $\Delta U$ = change in internal energy, $q$ = heat absorbed by system, $w$ = work done on system. ## Common Special Cases (Correct Expressions) **Isothermal process:** $\Delta U = 0$, so $q = -w$ ✓ **Adiabatic process:** $q = 0$, so $\Delta U = w$ ✓ **Constant volume process:** $w = 0$, so $\Delta U = q$ ✓ **Constant pressure process:** $q_p = \Delta H$ (Hess's Law) ✓ ## Why Option D is Incorrect Without seeing the specific options, typical **incorrect expressions** include: - $\Delta U = q - w$ (sign error; should be $q + w$) - $q = \Delta U - w$ for adiabatic (should be $\Delta U = w$) - $w = \Delta U + q$ (rearrangement error) **The most common wrong statement:** If option D reverses the sign convention or incorrectly rearranges the equation (e.g., $\Delta U = q - w$ instead of $\Delta U = q + w$), it violates the fundamental law because it doesn't correctly account for the thermodynamic sign convention where $w$ is work **done on** the system.