# 2020 P1 Q11 - Deduce Feasibility of Reaction at Different Temperatures

Let's take a look at 2020 A Levels H2 Chemistry Paper 1 Question 11.

We are asked to deduce if a reaction is spontaneous or feasible at different temperatures, given the signs of enthalpy change and entropy change.

Let's look at the equation that links Gibbs free energy, enthalpy change and entropy change.

ΔG = ΔH - TΔS

We can use this equation to deduce the sign of Gibbs free energy when signs of enthalpy change and entropy change are given.

Let's see how this is done for each of the statements.

For statement 1:

- endothermic hence enthalpy change is positive
- negative entropy change hence -TΔS is positive

Therefore Gibbs free energy is always positive and the reaction is not spontaneous at any temperature.

Hence statement 1 is false.

For statement 2:

- exothermic hence enthalpy change is negative
- positive entropy change hence -TΔS is negative

Therefore Gibbs free energy is always negative and reaction is spontaneous at all temperatures.

Hence statement 2 is true.

For statement 3:

- exothermic hence enthalpy change is negative
- negative entropy change hence -TΔS is positive

Therefore Gibbs free energy will be negative and reaction is spontaneous when temperature is low.

Hence statement 3 is false.

We can now run through the options and determine our answer.

Therefore the answer to this question is option C.

Topic: Energetics, Physical Chemistry, A Level Chemistry, Singapore

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