# Consider the following exothermic reaction 2SO₂₍g₎ + O₂₍g₎ ↔ 2SO₃₍g₎…

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## Consider the following exothermic reaction 2SO₂₍g₎ + O₂₍g₎ ↔ 2SO₃₍g₎If the temperature of the reaction is reduced from 800⁰C to 500°C, and no other change takes place, then

A. the reaction rate increases

B. concentration of SO₂ decreases

C. concentration of SO₂ increases

D. SO₂ gas becomes unreactive

B

## DETAILS…

It is very important we note that the reaction is exothermic.

For an exothermic reaction (negative change in H).

Increase in temperature favours the backward reaction, that is, more reactant(s) (SO₂ and O₂) will be formed.

But decrease in temperature favours the forward reaction, that is, more product(s) (SO₃) will be formed.

For an endothermic reaction (positive change in H).

Increase in temperature favours the forward reaction, that is, more product(s) (SO₃) will be formed.

But decrease in temperature favours the backward reaction, that is, more reactant(s) (SO₂ and O₂) will be formed.

Reducing the temperature will favour the forward reaction, leading to consumption of more SO₂ and O₂, and formation of more SO₃. So, the concentration of SO₂ decreases.

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### Now for the right answer to the above question:

1. Option A is incorrect. this option is not specific, the forward reaction rate will increase, but the reverse reaction rate will reduce. This option is not chosen because it does not specify if its forward or reverse reaction.
2. Option B is correct. concentration of SO₂ will decrease because the forward reaction will be favored.
3. C is incorrect. No, decreasing the temperature of an exothermic reaction favours the forward reaction, consuming more of the reactants.
4. D is not the correct answer.

## KEY-POINTS…

• For exothermic reactions, decreasing the temperature will decrease the concentration of reactants and increase the concentration of products.

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/ culled from 2015 JAMB-UTME Chemistry past question 40 /

##### Consider the following exothermic reaction 2SO₂₍g₎ + O₂₍g₎ ↔ 2SO₃₍g₎... » QuizTablet

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