Entropy change help please!!?

[匿名]

2016-06-20 5:21 am

For each of the following, predict with justification whether there's an increase or decrease in entropy for the system.
Thank you so much for any help you can give, I am including my guesses for some of these, however I especially need help with the reasoning

a. a diatomic molecule dissociates into two atoms- would that be an increase, bc energy is absorbed?
b. humidity condenses in cold air- decrease, bc decrease in heat?
c. the reaction N2(g) + 3H2(g) --> 2NH3(g) - decrease, bc heat is released when the bonds form?
d. perfume vapors diffuse through a room- NO CLUE AT ALL
e. the reaction NH4NO3(s) + H2O(l) --> 2NH3(g) + O2(g) - I have no idea for this one, but maybe an increase bc both the solid and liquid have changed to gases?
f. silver chloride precipitates from aqueous solution- I think it would decrease because if the system goes from liquid to solid there's probably a decrease in energy?

回答 (1)

fooks

2016-06-20 5:49 am

✔ 最佳答案

Entropy is a measure of "degree of randomness". The more random, the higher the entropy is.
So, think about the change in degree of randomness, but not the energy change.

a. increase
A molecule dissociates into two atoms. The degree of randomness increases due to the increase in number of particles .

b. decrease
When water vapor condenses to liquid water, the degree of randomness decreases because liquid molecules move less freely than gaseous molecules.

c. decrease
In the equation, 4 moles of gaseous molecules are consumed and 2 moles of gaseous molecules are produced. Gas molecules are freely and randomly moving. The decrease in number of gaseous molecules leading to a decrease in randomness.

d. increase
When perfume vapor diffuse to a larger volume, the degree of randomness increases.

e. increase
In the equation, No gaseous molecule is consumed and 3 moles of gaseous molecules are produced. Gas molecules are freely and randomly moving. The increase in number of gaseous molecules leading to an increase in randomness.

f. decrease
Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
The Ag⁺(aq) and Cl⁻(aq) ions are mobile in solutions, while the ions in AgCl(aq) are not mobile. In precipitation, the mobility of ions decreases and thus the degree of randomness decreases.

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