Answer: a decrease in volume will shift the equilibrium towards the reactant's side.
Step-by-step explanation:
The question requires us to determine the direction to which the following reaction should shift when the volume of the system is decreased:
1A(s) + 2B(l) + heat ↔ 3C (g) + 4D (s)
According to Le Chatelier's principle, a change in temperature, pressure, volume or concentration of reactants/products of a system will result in a predictable change to the system as an attempt to restabilish the equilibrium state.
Considering the change in volume and pressure, we have that decreasing the pressure (or increasing the volume) of the system, the production of additional moles of gas will be favoured, thus the reaction will shift towards the direction with greater amount of moles gas. Similarly, an increase in pressure (or decrease in volume) will shift the equilibrium to favor the side with fewer moles of gas.
Considering the reaction given, we can see from the chemical equation that there are 0 moles of gas on the reactant's side (left side) and 1 mol of gas on the product's side (right side). Therefore, a decrease in volume will shift the equilibrium towards the reactant's side.