View Full Version : quick MCAT problem...can't figure answer


ronaldo23
02-03-2008, 09:32 PM
got it thanks

adamber
02-03-2008, 09:35 PM
C?

Waterlilies
02-03-2008, 09:39 PM
c :)

ronaldo23
02-03-2008, 09:41 PM
why?

adamber
02-03-2008, 09:44 PM
A cannot be correct, because the second law of thermo is never violated. D is incorrect, because deltaG= deltaH- TdeltaS, and delta S is decreasing, so overall it will be positive deltaG, which is non-spontaneous. B is backwards, because if the entropy of the system is decreasing, then the entropy of the surrounding must be increasing, since that maintains the second law of thermo.

biggiesmallsiz
02-03-2008, 09:44 PM
why?

evaporation = lots of gas molecules = lots of entropy adding to the universe

SketchLazy
02-03-2008, 09:47 PM
When dissolved sugar is recrystallized by evaporating the water, its entropy decreases. A crystal is more ordered than particles in solution. In terms of thermodynamics, this must mean that

A the second law of thermodynamics is broken.
B the entropy of some other part of the system is increased.
C the entropy of the universe is increased.
D evaporation will occur spontaneously.

I think it's B. The water that is dissolving the sugar is also part of the system. When it evaporates, its entropy increases because it is becoming a gas.

biggiesmallsiz
02-03-2008, 09:54 PM
I think it's B. The water that is dissolving the sugar is also part of the system. When it evaporates, its entropy increases because it is becoming a gas.


its def C jesus christ. do you have the answer?

adamber
02-03-2008, 09:57 PM
I think it's B. The water that is dissolving the sugar is also part of the system. When it evaporates, its entropy increases because it is becoming a gas.

The water is part of the system originally, but when it evaporates, the gas molecules contribute to the entropy of the surroundings by spreading out further.

Revilla
02-03-2008, 10:31 PM
Another vote for C here.