I\'m writting a report on my electrochemical lab and trying to explain why the v
ID: 487683 • Letter: I
Question
I'm writting a report on my electrochemical lab and trying to explain why the voltage increased when the temperature increased. I'm not sure I have the concept done correctly though. Below is my explaination regarding this, can someone please review it and provide insight? Thanks in advance
"The experimental data gathered illustrated an increase in voltage as the temperature of the system increases. This in contradictory of the expectations seen in the Nernst equation, which illustrates a decrease in cell potential as the temperature increases. Although temperature plays an important role Nernst equation, it also has a role within several components used to derive the Nernst equation. As stated earlier, the free energy for this process was a positive value, which indicates a negative change in entropy. Entropy is inversely proportional to temperature, so as the temperature of the system increased the change in entropy approached a more positive value allowing the voltage to increase as well."
Explanation / Answer
Your explanation is not correct. Because this depends totally on how you write the Nernst equation the temperature might increase or decrease the potential of the cell.
It depends more on the reaction quotient than on anything else.
Ecell = Eocell - (RT/nF) ln Q
aA + bB --> cC + dD
Q = reaction quotient= ([C]^c * [D]^d)/ ([A]^a * [B]^b)
The temperature comes into the equation as a scaling factor where RT/nF has units Volt. This essentially defines how much the voltage changes per a decade change in the reaction quotient. The temperature dependence here is just a matter of the scaling factor.
Please check your electrochemical reaction and see the temperature dependency accordingly.
"As stated earlier, the free energy for this process was a positive value, which indicates a negative change in entropy."
Gchange in free energy=Hchange in enthalpyTS(temperature) change in entropy
So, G has two components, one is H and TS. It does not totally depend on entropy function.
"Entropy is inversely proportional to temperature, so as the temperature of the system increased the change in entropy approached a more positive value allowing the voltage to increase as well"
S=nCmln(Tf/Ti)
As said above, the potential does not only depend on the change in entropy. In your statement, entropy change should be inversely proportional to temperature. So, change in entropy decreases with increasing temperature.