[salpar]

Hello everyone.

This problem is a major pain in the ass.

What is the change in free energy at 298k when 83.9mL of 0.693 M calcium chloride is combined with 10.2 mL of 0.289 M sodium carbonate? (R=8.31 j/K mol)

Im also given this:

Ca²⁺(aq)+CO₃^2-  CaCO₃(s)

ΔG°f Ca²⁺ (aq)= -553.5 kJ/mol @298K
ΔG°f CO₃^2- (aq)= 527.9 kj/mol @298K
ΔG°f CaCO₃(s) = -1128.8 kJ/mol   @298K

Cant find any problem like this on the web. Please help. Thank you!


Also I can show the work Ive done but it all leads to a dead end.

The problem is I dont know how to relate the given reaction to the reaction I am interested in, aside from the fact that there is CaCO3(s) in both ..

Here is the reaction I came up with for the one Im interested in.

CaCl2(aq) + Na2CO3(aq)  CaCO3(s) + 2NaCl(aq)

I know I am looking for the ΔG at non standard conditions and I know that the formula I have to use is ΔGrxn=Δ°Grxn+ nRTlnQ

I MIGHT be able to get Δ°Grxn just looking at standard tables. I have R and T , but Q is giving me a huge problem!


Is it possible this problem was a misprint in the book?

I mean the equation they give has nothing to do with what theyre asking for.

[Dan]

I think you are overthinking it. Start by constructing a thermodynamic cycle (like a Hess cycle) and find the molar free energy change of reaction.

[salpar]

Didnt help.

[Dan]

Show what you did (Forum Rule). Did you look up Hess cycles?

[Babcock_Hall]

I would start by writing out the chemical equations for each process.  There is an almost magical connection among the hand, the eye, and the brain.