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A reaction is exothermic and has a negative entropy change - AQA - A-Level Chemistry - Question 32 - 2017 - Paper 3

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A reaction is exothermic and has a negative entropy change. Which statement is correct? A The reaction is always feasible B The reaction is feasible above a certain... show full transcript

Worked Solution & Example Answer:A reaction is exothermic and has a negative entropy change - AQA - A-Level Chemistry - Question 32 - 2017 - Paper 3

Step 1

The reaction is exothermic and has a negative entropy change.

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Answer

For a reaction to be feasible, we need to consider the Gibbs free energy change, given by:

riangleG=riangleHTriangleS riangle G = riangle H - T riangle S

Where:

  • riangleG riangle G is the Gibbs free energy change,
  • riangleH riangle H is the enthalpy change,
  • TT is the absolute temperature in Kelvin,
  • riangleS riangle S is the entropy change.

In our case, the reaction is exothermic, which means riangleH riangle H is negative. However, since the entropy change is negative, riangleS riangle S is also negative.

As the temperature increases, the magnitude of the TriangleST riangle S term becomes significant and can lead to a situation where riangleG riangle G becomes positive, which indicates that the reaction is not feasible at higher temperatures. Thus, the reaction can only be feasible below a certain temperature. Therefore, the correct statement from the options is:

C: The reaction is feasible below a certain temperature.

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