The Top 5 NEET Traps

Trap 1: $\Delta G$ vs $\Delta G^\circ$ at Equilibrium The single most tested concept in NEET thermodynamics. At equilibrium: $\Delta G = 0$ (always). $\Delta G^\circ = -RT\ln K$ (non-zero unless $K = 1$). Students who confuse these lose 4 marks on a critical question.

Trap 2: $\Delta n_g$ Includes Solids and Liquids Wrong! Only gaseous moles are counted. For $CaCO_{3}$(s) → CaO(s) + $CO_{2}$(g): $\Delta n_g = 1$ (not 2 - 1 = 1 counting the wrong way). Always write out all gaseous species first, then count.

Trap 3: Work Sign in Expansion In IUPAC (NCERT): expansion gives $w < 0$ (negative, work done BY system). Many students incorrectly write $w > 0$ for expansion. Mnemonic: "W-ON positive" — work ON the system is positive.

Trap 4: Using °C Instead of K in Gibbs Equation $T$ in $\Delta G = \Delta H - T\Delta S$ MUST be in Kelvin. Using 25 instead of 298 gives a completely wrong answer. Always convert: $T(K) = T(°C) + 273$.

Trap 5: Standard State of Carbon $\Delta H_f^\circ(C, \text{diamond}) \neq 0$. The standard state of carbon is graphite. $\Delta H_f^\circ(C, \text{graphite}) = 0$. Diamond is a non-standard allotrope with $\Delta H_f^\circ = +1.9$ kJ/mol.

Quick Verification Checklist

Before submitting a thermodynamics problem:

• Is temperature in Kelvin?
• Did I count only gaseous moles for $\Delta n_g$?
• Is the sign of work consistent with IUPAC convention?
• Did I use $\Delta G = 0$ (not $\Delta G^\circ$) for equilibrium?
• Are the units consistent throughout (J vs kJ)?