At equilibrium, which of the following reactions is not affected by pressure?

Correct answer: A. ½ N2(g) + ½ O2 (g) ⇌ NO(g)

  • A. ½ N2(g) + ½ O2 (g) ⇌ NO(g)
  • B. PCl5(g) ⇌ PCl3(g) + Cl2(g)
  • C. 2NO2 (g) ⇌ N2O4(g)
  • D. SO2Cl2(g) ⇌ SO2(g) + Cl2(g)

Explanation

Pressure affects only reactions where the number of gas moles changes. In option A, reactants have 1 mole of gas total (0.5 + 0.5), and the product also has 1 mole. Since gas moles are equal on both sides, pressure has no effect on this equilibrium.

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About Chemical Equilibrium

Reversible reactions reach dynamic equilibrium when forward and reverse rates become equal, and Le Chatelier's principle predicts the effect of changing concentration, pressure or temperature. The chapter also covers solubility product, the common ion effect, buffer action and the conditions used in Haber's process, with equilibrium shifts distinguished from changes in the equilibrium constant.

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