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Question:

Predict in which of the following entropy decreases?

Temperature of a crystalline solid raised from 0K to 115K.

A liquid crystallizes into a solid.

2NaHCO3(s)→Na2CO3(s)+CO2(g)+H2O(g)

H2(g)→2H(g)

Solution:

After freezing, the molecules attain an ordered state and, therefore, entropy decreases. Option 2, when the temperature is increased, the entropy of the system increases. Option 3, 2 moles giving 3 moles, entropy increases. Option 4, 1 mole giving 2 moles, entropy increases.