What is the free energy change of...?

Question

Hi, i'm wondering if someone could answer this question for me.

What is the free energy change (triangle)G?

Zn(s) + Cu2+ -> Zn2+ + Cu(s)

Please show your work, as i have the answer in a sample work book, i just don't know how to get the answer.

thanks for helping.

Answer 1

i think the free enrgy change 0 because if you compare the amount of each reactants to the products, you can see the zinc has doubled but the copper has halved, balancing it out.

or maybe you have to look at the enthalpy change of reaction using hess's cycle?

Answer 2

We can easily calculate Eo using standard reduction potentials. delta Go is then calculated by :  delta Go = -nFEo

Zn(s)  =>  Zn2+ + 2e-          Eo = +0.76 V

Cu2+ + 2e-  =>  Cu(s)         Eo = +0.34 V

================================

------------------------------------Eo = +1.10 V

delta Go = -nFEo = -(2 moles)(96500 C / mole)(1.10 V ) = -212,300 C.V = -212,300 J =  -212.3 kJ

Note that since the Eo is + (a spontaneous reaction), that delta G is very negative (also indicative of a spontaneous reaction).