Free response · Unit 7 Beta

Equilibrium in a decomposing gas

Short free response · 4 points

The question

Name: ______________________   Date: ____________   Equilibrium in a decomposing gas (4 points)

Experimental setup

Phosgene decomposing in a sealed flask

Phosgene decomposes on heating: COCl2(g) ⇌ CO(g) + Cl2(g). At a certain high temperature, Kc = 8.0 × 10−4. A sealed 1.00 L flask initially contains 0.50 M COCl2 and no CO or Cl2, and is held at that temperature.

  1. (a) Write the equilibrium concentration of each species in terms of x, where x is the amount of COCl2 that reacts (in M). [1 point]

  2. (b) Calculate [Cl2] at equilibrium. [1 point]

  3. (c) Justify the approximation you used in part (b), or explain why none was needed. [1 point]

  4. (d) Extra CO is injected into the equilibrium mixture at constant temperature. Determine whether [COCl2] increases, decreases or stays the same, and justify your answer in terms of Q and K. [1 point]