Predict how the entropy of the substance is affected in the following processes:

a) O2 (g,200 kPa, 300k) --> O2 (g, 100, 300k)

b)Br2 (l, 1 bar, 25 degree C) --> Br2 (g, 1 bar, 25 degree C)

C)Fe (s, 1 bar, 250 degree C)--> Fe(s, 1 bar, 25 degree C)

will entropy either be increase, decrease, or remain the same?

I am quite confused on this because I know that pressure would cause positional disorder and temperature will cause thermal disorder. But I don't really understand how it correlates with entropy. I tried to do the problem and I got a) increase, b) remain the same, and c) decrease. But I don't know if that is correct or not. Please explain because I am just guessing I don't really have a reason behind my guess. Thanks

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Thank you. I understand it a lot better. And as for equation, I figure that I figure that I left out the kPa. so that for the first process, there is a decrease in pressure so more movement for the molecules therefore S increases, right?

Yes, for increase in P there is a decrease in S.

Well, let me try to clown around and explain it to you!

a) In the first process, O2 gas is going from 200 kPa to 100 kPa at constant temperature. So, the pressure is decreasing, meaning the gas molecules are able to move around more freely. This results in an increase in positional disorder or freedom of movement, leading to an increase in entropy. So, your guess of an increase in entropy is correct! Good job!

b) Now, let's look at the second process. Br2 liquid is changing into Br2 gas at 1 bar and 25 degrees Celsius. The change is happening at constant pressure and temperature. When a liquid turns into a gas, the molecules become more spread out and have more freedom to move. This increase in freedom of movement results in an increase in positional disorder, contributing to an increase in entropy. So, your guess of the entropy remaining the same is not quite right. It actually increases! Time to brush up on your clown knowledge!

c) Finally, we have the third process, where solid iron (Fe) is going from 1 bar and 250 degrees Celsius to 1 bar and 25 degrees Celsius. Here, the temperature is decreasing, but the pressure and physical state (solid) are remaining the same. As the temperature decreases, the thermal energy of the particles decreases, reducing their random movement. This results in a decrease in thermal disorder and thus a decrease in entropy. So, your guess of a decrease in entropy is spot on! You really nailed it!

Remember, changes in pressure, temperature, and physical state can all affect the entropy of a substance. So, keep practicing and soon you'll be the clown expert in thermodynamics!

To determine how the entropy of a substance is affected in a given process, it is important to consider the factors that influence entropy, such as changes in temperature, pressure, and phase. Let's analyze each process separately:

a) O2 (g, 200 kPa, 300K) --> O2 (g, 100 kPa, 300K)
In this process, the pressure of O2 decreases while the temperature remains constant. When pressure decreases, the volume of the gas molecules tends to increase, leading to increased positional disorder and increased entropy. Therefore, the entropy of O2 will increase.

b) Br2 (l, 1 bar, 25°C) --> Br2 (g, 1 bar, 25°C)
In this process, the liquid bromine (Br2) is converted into gaseous bromine (Br2) at constant pressure and temperature. When a substance changes phase from liquid to gas, its molecular arrangement becomes more disordered, resulting in an increase in entropy. Therefore, the entropy of Br2 will increase.

c) Fe (s, 1 bar, 250°C) --> Fe (s, 1 bar, 25°C)
In this process, solid iron (Fe) undergoes a temperature decrease while the pressure remains constant. As the temperature decreases, the kinetic energy of the iron atoms decreases, resulting in decreased thermal disorder and reduced entropy. Therefore, the entropy of Fe will decrease.

So, your answers are correct:
a) The entropy of O2 will increase.
b) The entropy of Br2 will increase.
c) The entropy of Fe will decrease.

A. With increased pressure volume decreases so the molecules have less space to move around in. S decreases. T is same so that doesn't enter into the problem.

B. T and P remains same. The only difference is liquid vs gas. As a gas there is MUCH more volume to move around and S increases.

C. P and solid are same. Only change is T. Lower T always means less S. There is less kinetic motion with decreasing T.