[divexo]

Hi,

I have two quick questions with what i was thinking in italics, so you know i did try a bit!

1. What is K if ΔG° = -18.0 kJ for a reaction at 25°?
i know K=e^(ΔG°/RT) but what is the ΔG° value, is it in kj? and what is RT!

2. For the process of freezing liquid methanol, CH3OH, at a given temperature and pressure,
 a. ΔH is negative and ΔS is positive.
 b. ΔH is negative and ΔS is negative.
 c. ΔH is positive and ΔS is negative.
 d. ΔH is positive and ΔS is positive.
I thought they were both negative for freezing water, but not sure about methanol?

Thank you!

[opti384]

1. What is K if ΔG° = -18.0 kJ for a reaction at 25°?
i know K=e^(ΔG°/RT) but what is the ΔG° value, is it in kj? and what is RT!
[

Well, ΔG° = -18.0 kJ is given in your question. T will be the temperature which is expressed in K(Kalvin) in chemistry. R is the universal gas constant.

2. For the process of freezing liquid methanol, CH3OH, at a given temperature and pressure,
 a. ΔH is negative and ΔS is positive.
 b. ΔH is negative and ΔS is negative.
 c. ΔH is positive and ΔS is negative.
 d. ΔH is positive and ΔS is positive.
I thought they were both negative for freezing water, but not sure about methanol?

Do you know why its negative for freezing water?

[divexo]

Thanks for fast reply.

for 1. i did e^(-18/(8.31*298)) and got 9.9x10^-1 and apparently that isn't right...

2. I have no idea about that question... i just heard that it was negative both for water, but not why.. please explain?

[Yggdrasil]

For #1, check your units.  The numerator and denominator of ΔG°/RT should have the same units.

For #2, is the freezing of water (or any other substance) generally exothermic or endothermic?  Which has more entropy, a liquid or a solid?

[divexo]

1. I still can't get the right answer for this

2. Hmm, when temperature goes down, it releases heat to become more of a solid, so exothermic? And entropy of a solid is less as it's more ordered.

[sjb]

1. I still can't get the right answer for this

What are the units of R, and of T?

[divexo]

1. I still can't get the right answer for this

What are the units of R, and of T?

I did it before "e^(-18/(8.31*298)) and got 9.9x10^-1" in the above message.
And have tried to fiddle around, i know these units now but not getting the correct answer.

[sjb]

I did it before "e^(-18/(8.31*298)) and got 9.9x10^-1" in the above message.
And have tried to fiddle around, i know these units now but not getting the correct answer.

18 what? 8.31 what? 298 what?

[sjb]

Let's try a slightly different tack. If a cup of petrol allows you to travel 50 metres, and you have to travel 425 kilometres, how much petrol do you need?

[divexo]

:p thanks i got it.