What stress will shift the following equilibrium system to the left?

2SO2 (g) + O2 (g) ⇌ 2SO3 (g); ΔH = - 98.8 kJ/mol

Decreasing concentration of SO3

Decreasing volume

Increasing concentration of SO2

Increasing temperature

Answer: Increasing temperature

Explanation:

The Principle of Le Chatelier states that if a system in equilibrium is subjected to a change of conditions, it will move to a new position in order to counteract the effect that disturbed it and recover the state of equilibrium.

The variation of one or several of the following factors can alter the equilibrium condition in a chemical reaction:

Temperature The pressure The volume The concentration of reactants or products

In the case of the reaction in the question, the change that moves the balance to the left will be the one that moves it towards the reagents, that is, that favors the production of reagents instead of products.

Decreasing the concentration of SO3 and increasing the concentration of SO2 will favor the production of SO3, which is the product of the reaction. Decreasing the volume increases the pressure of the system and the balance will move to where there is less number of moles. In the case of the reaction in question, we have 3 moles of molecules in the reactants (1 mole of O2 + 2 moles of SO2) while in the products there are 2 moles of SO3 only, therefore, decreasing the volume will displace the balance to the right, which corresponds to the sense in which there is less number of moles.

The reaction of the question is an exothermic since ΔH <0, therefore in the reaction heat is produced and it can be written in the following way,

2SO2 (g) + O2 (g) ⇌ 2SO3 (g) + heat

So, if we increase the temperature we will be adding heat to the system, so the balance would move to the left to compensate for the excess heat in the system.