Equilibrium: Le Chatelier's Principle and CaCO3 Decomposition

[Zayn]

Homework Statement

I had a question on a test and I got the wrong answer, but I still don't understand why. It was a Le Chatelier problem about the equilibrium shift, and it described the decomposition of CaCO3

CaCO3(s) <->CaO(s) + CO2(g)

The question asked something along the lines of "If the volume of the container was halved, in what direction would equilibrium shift?"

Homework Equations

N/A

The Attempt at a Solution

I thought it wouldn't shift at all because the CO2 is in a different state than the CaCO3 and CaO, and because one of the ways you can change an equilibrium system without disturbing the equilibrium was to have reactants in different states, but apparently I was wrong. Can you please explain to me why the equilibrium would shift left even if there are no gas entities? Is it just to reduce pressure because there is 1 reactant entity for every 2 product entities? Thanks.

 

[Chestermiller]

The equilibrium is determined solely by the equilibrium value of the CO2 gas partial pressure. If the container volume is halved, half of the CO2 will have to react with CaO to re-establish the equilibrium partial pressure.