# Heat energy vs. electrical energy in a galvanic cell or in an electrochemical reaction

How can someone determine heat energy released during an electrochemical reaction?

Let's assume a simple galvanic cell at standard environment:

$$\ce{Zn(s) -> Zn^2+(aq) || Cu^2+(aq) -> Cu(s)}$$

Electrical energy can be derived from the electrode potential and electron flow, but how the heat release can be calculated? What's the heat release when $\ce{Zn(s)}$ gets solvated to $\ce{ZnSO4(aq)}$, and whats the heat release when $\ce{Cu^2+}$ ions gets plated to the electrode?

I'm using term "heat release", because I get confused about the enthalpy in electrochemical cells, since some of enthalpy seems to be connected to electrical work as well.

• I will write a proper answer if I have the time, but Bard&Faulkner has a great discussion of this phenomenon in the beginning of Chapter 2. If you have access to a library that has it, it is section 2.1.2 – Burak Ulgut Apr 11 '17 at 12:31

Operational electrochemical cells have $\pu{\Delta G = -ve}$

And, $\pu{\Delta G = - nFE}$
$\pu{\Delta G = \Delta H - T\Delta S}$

Knowing the entropy change, enthalpy change could be calculated

or

$\pu{\Delta H = -nFE + nFT{d\Delta G}/dT}$ [at contant P]

• Hey, Thanks for the answer. However, does this imply that you could use Nernst equation to determine the temperature coefficient? Or is Nernst equation too much of an approximation and cant be used to determine the heat release? – kpeteL Apr 16 '17 at 12:12
• No, It is not at all approximation Just AT CONSTANT PRESSURE, we have used Thermodynamics of the cell to correlate (delta)S with (delta)G of the cell Which gives the last relation mentioned We of course, ultimately are going by Nernst equation only! – Che Mistry Apr 17 '17 at 2:47