# Change in GIbbs free energy for ethanol

1. May 7, 2005

### koomanchoo

hey i seem to be having a lot of trouble with this type of question:
Calculate the change in Gibbs energy of 35g of ethanol (mass density = 0.789g cm-3) when the pressure is increased isothermally from 1 atm to 3000 atm.

in my notes i have that dG=V(Pf-Pi) and search up on the net that mass=volume*density so volume of ethanol comes to 35/.789 the answer is suppose to be 10.4kJ but i get nowhere near it.

dG=(35/.789)*(3000-1) is this the right equation because thats all i can find
pls help me! thanks
P.K

2. May 7, 2005

### dextercioby

Okay.Maybe

$$\Delta G=V\Delta p$$

sounds right.I'm sure you need to convert all units into SI-mKgs.

1 atm=101,325 Pa
1 cm^{3}=10^{-6}m^{3}

1kJ=1000J

Daniel.

3. May 7, 2005

### koomanchoo

thanks man

Thanks heeeeeeeeeaps! Daniel
you made my day. spent ages doing that Q like hours and hours just seraching what i was doing wrong. thanks again.
this forum rOcks!!

4. May 7, 2005

### dextercioby

Please,do not double post.You should have asked it in one single forum.I think Classical Physics was the appropiate choice...

Daniel.