For the reaction, N₂O₄⇌ 2NO₂, graph is plotted as shown below. Identify correct statements.
A. Standard free energy change for the reaction is -5.40 kJ mol⁻¹.
B. As ΔG⊖ in graph is positive, N₂O₄ will not dissociate into NO₂ at all.
C. Reverse reaction will go to completion.
D. When 1 mole of N₂O₄ changes into equilibrium mixture, value of ΔG⊖=-0.84 kJ mol⁻¹
E. When 2 mole of NO₂ changes into equilibrium mixture, ΔG⊖ for equilibrium mixture is -6.24 kJ mol⁻¹.
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 3 steps

Read the curve as a valley: from either end, the mixture slides downhill to E and stops there.

1. Read the graph. Point A is pure N₂O₄, with nothing dissociated. Point B stands for pure NO₂, that is 2 mol of it. Point E, the lowest point, is the equilibrium mixture.
2. Standard free energy. Δ G⊖ compares pure products with pure reactants, so it is G_B - G_A. B lies 5.40 above A, so Δ G⊖ = +5.40 kJ mol⁻¹. A positive value only means K < 1. It does not mean that no reaction happens.

   G_E - G_B = -(5.40 + 0.84) = -6.24 kJ mol⁻¹

   Statement	What the graph shows	Verdict
   A	A to B goes uphill, so the value is +5.40, not -5.40	wrong
   B	G still falls from A to E, so some N₂O₄ dissociates	wrong
   C	Starting from B, G falls only until E, so the reverse reaction stops at equilibrium	wrong
   D	A to E drops by 0.84, giving -0.84 kJ mol⁻¹	correct
   E	B to E drops by 5.40 + 0.84, giving -6.24 kJ mol⁻¹	correct

3. So. Only D and E are correct, which is option (b).

The idea to keep. Pure reactant and pure product are the two ends of the G curve, and equilibrium is its lowest point. A positive Δ G⊖ means K < 1, never that no reaction happens.

Answer from the NTA final answer key. Solution by PrepWiser.