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# Chemistry: entropy watch

1. 1. Is it reasonable to expect a cold cup of tea to warm up spontaneously?explain your answer.

2.Tidying a room reduces its entropy. Does this process contravene the second law of thermodynamics?

3. Arrange the following in ascending order of entropy:
steam ar 110 degree celcius;
ce at -10 degree celcius;
water at 30 degree celcius

Can anyone tell me if my answers are correct or not?

1. No, it is not. Since a cold cup of tea would need heat to become warm. It's endothermic in way.

2. Yes, since order can only become disorder, and disorder can't become orderly.

3. ice<water<steam
2. (Original post by Mme_Bonii)
1. Is it reasonable to expect a cold cup of tea to warm up spontaneously?explain your answer.

2.Tidying a room reduces its entropy. Does this process contravene the second law of thermodynamics?

3. Arrange the following in ascending order of entropy:
steam ar 110 degree celcius;
ce at -10 degree celcius;
water at 30 degree celcius

Can anyone tell me if my answers are correct or not?

1. No, it is not. Since a cold cup of tea would need heat to become warm. It's endothermic in way.

2. Yes, since order can only become disorder, and disorder can't become orderly.

3. ice<water<steam
The second law of thermodynamics states that the universal entropy must increase

1. To heat up the cup would require absorption of heat from the surroundings REDUCING its entropy. This could not be compensated for by the increase in the cup's entropy as the surroundings are much bigger.

2. This does not contravene the second law otherwise it would not be possible. The decrease in the entropy of the room is more than compensated by the vast increase in entropy of the surroundings caused by the energy required and dissipated in organising and tidying the room.

3. correct
3. (Original post by charco)
The second law of thermodynamics states that the universal entropy must increase

1. To heat up the cup would require absorption of heat from the surroundings REDUCING its entropy. This could not be compensated for by the increase in the cup's entropy as the surroundings are much bigger.

2. This does not contravene the second law otherwise it would not be possible. The decrease in the entropy of the room is more than compensated by the vast increase in entropy of the surroundings caused by the energy required and dissipated in organising and tidying the room.

3. correct
in answer two, how does the entropy of the surroundings increase? and what are the surroundings?
4. (Original post by Mme_Bonii)
in answer two, how does the entropy of the surroundings increase? and what are the surroundings?
In consideration of the universal entropy we define the terms:

1. Universe
2. System
3. Surroundings

The universe is literally everything
The system refers to the particles under study
The surroundings refers to that part of the universe which is not the system

Entropy is a function of microstates produced by the disorder of heat energy and particles

Hence

Universal entropy = system entropy + surroundings entropy

and consequently any change in the RHS equals the same change on the LHS

ΔS(universe) = ΔS(system) + ΔS(surroundings)

When an exothermic reaction occurs in the system, chemical potential energy turns to heat energy and this increases the entropy of the surrroundings, without affecting the particles of the system.

So if ΔH(sys) is negative then ΔS(surroundings) is positive and is given by -ΔH(sys)/T

substituting the surroundings entropy change

ΔS(universe) = ΔS(system) - ΔH(system)/T

Now multiply through by -T to remove the fraction

-TΔS(universe) = -TΔS(system) + ΔH(system)

rearrange

-TΔS(universe) = ΔH(system) - TΔS(system)

You now have an expression relating the absolute entropy of the universe to only changes occuring in the system.

For the universal entropy to increase (as it must in accordance with the second law of thermodynamics) the whole of the LHS term MUST be negative.

This left hand side is called Gibbs free energy, ΔG

ΔG = ΔH - TΔS

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