Chem Lab C

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kenniky
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Re: Chem Lab C

Postby kenniky » February 13th, 2017, 6:57 pm

According to the second law of thermodynamics, entropy must always increase. How is it, then, that it is possible for water to freeze and become ice? Justify your response using both an equation and a direct reference to the second law of thermodynamics.
Answer
(d = delta, I'm too lazy to find the character) The second law of thermo states that the energy of the universe must increase. However, the water is a system. dS_system + dS_surroundings = dS_universe > 0, so as long as the change in the entropy of the surroundings is large enough to offset the loss of entropy of the freezing water, it should work
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Avogadro
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Re: Chem Lab C

Postby Avogadro » February 14th, 2017, 3:39 am

According to the second law of thermodynamics, entropy must always increase. How is it, then, that it is possible for water to freeze and become ice? Justify your response using both an equation and a direct reference to the second law of thermodynamics.
Answer
(d = delta, I'm too lazy to find the character) The second law of thermo states that the energy of the universe must increase. However, the water is a system. dS_system + dS_surroundings = dS_universe > 0, so as long as the change in the entropy of the surroundings is large enough to offset the loss of entropy of the freezing water, it should work
Correct, though you might want to clarify that the change in entropy of the surroundings is caused by it being exothermic and you could also use the equation dG= dH- TdS if you wanted to.

Your turn!
Lower Merion 2017
Subtitled: Revenge of the Non-Harriton

Placement Record:

Code: Islip | Conestoga | Tiger | Regionals | States
Out of: 61 | 42 | 36 | 37 | 36

Chemistry Lab: 9 | - | - | 4 | 4
Astronomy: 14 | - | 5 | 10 | 3
Material Science: 12 | 19 | 9 | 5 | 9
Optics: 14 | 7 | 3 | 4 | 2

Avogadro
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Re: Chem Lab C

Postby Avogadro » March 9th, 2017, 5:53 pm

Or I guess I'll write one so as to keep this going :P

A 3.4 mole sample of ammonia is kept in a 0.2 liter cylindrical container at a temperature of 50 K.
a. What is the average kinetic energy of one of the ammonia molecules?
b. What is the pressure of the container?
c. Why might the value you calculated in part b not be 100% accurate?
Lower Merion 2017
Subtitled: Revenge of the Non-Harriton

Placement Record:

Code: Islip | Conestoga | Tiger | Regionals | States
Out of: 61 | 42 | 36 | 37 | 36

Chemistry Lab: 9 | - | - | 4 | 4
Astronomy: 14 | - | 5 | 10 | 3
Material Science: 12 | 19 | 9 | 5 | 9
Optics: 14 | 7 | 3 | 4 | 2


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