Question

# The entropy change can be calculated by using the expression, â–³S=QrevT. When water freezes in a glass beaker, choose the correct statement amongst the following:

A
Ssystem decreases but Ssurroundings remains the same.
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B
Ssystem increases but Ssurroundings decreases.
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C
Ssystem decreases but Ssurroundings increases.
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D
Ssystem decreases and Ssurroundings also decreases.
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Solution

## The correct option is C △Ssystem decreases but △Ssurroundings increases.Freezing of water is an exothermic process (heat releases). As water freezes from liquid to solid, randomness (or entropy) decreases, i.e., △Ssystem decreases. Heat released during the process, is absorbed by the surroundings hence, △Ssurroundings increases. Theory: Second Law of Thermodynamics: It states that as energy is transferred or transformed, more and more of it is wasted. The Second Law also states that there is a natural tendency of any isolated system to degenerate into a more disordered state. Note: Entropy of universe increases in the course of a spontaneous change. ΔSuniv. is greater than 0 ΔSuniv.=ΔSsys+ΔSsurr > 0 For a spontaneous process in an isolated system, Entropy always increases Also, When a system is in equilibrium, the entropy is maximum and the change in entropy, ΔS=0.

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