A vessel at 1000 K contains CO₂ with a pressure of 0.5 atm . Some of CO₂ is converted into CO on addition of graphite. If total pressure at equilibrium is 0.8 atm , then Kₚ is :

Solution

Chemistry ma’am · 4 steps

Graphite is a solid, so it stays out of Kp. Let x atm of CO2 react and the pressure rise gives you x.

1. Write the reaction. Graphite reduces CO₂: CO₂(g) + C(s) ⇌ 2CO(g). Carbon is a pure solid, so it does not appear in Kₚ.
2. Set up pressures. If x atm of CO₂ reacts, it leaves 0.5 - x atm of CO₂ and forms 2x atm of CO. The total is (0.5 - x) + 2x = 0.5 + x.
3. Find x. 0.5 + x = 0.8, so x = 0.3. At equilibrium p_(CO₂) = 0.2 atm and p_(CO) = 0.6 atm.

   Kₚ = (p_(CO))²/p_(CO₂) = (0.6)²/0.2 = 0.36/0.2 = 1.8 atm

4. So. Kₚ = 1.8 atm, which is option (d).

The idea to keep. When one gas turns into more moles of gas, the rise in total pressure tells you the extent of reaction. Leave pure solids out of Kₚ and raise each pressure to its coefficient.

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