The EMF of a certain galvanic cell is found to increase when the temperature is raised. Which statement about the cell reaction is correct?

A $Δ_{r} S > 0$ , and when the cell is operated reversibly it absorbs heat from the surroundings
B $Δ_{r} S < 0$ , and when the cell is operated reversibly it releases heat to the surroundings
C $Δ_{r} S > 0$ , and $Δ_{r} H$ is more negative than $Δ_{r} G$
D $Δ_{r} S = 0$ , since EMF depends only on $Δ_{r} G$

Answer: A

Δ_{r} S = n F (\partial E / \partial T)_{P}

, so a rising EMF means

Δ_{r} S > 0

. For reversible operation the heat exchanged is

q_{rev} = T Δ_{r} S > 0

, i.e. heat is absorbed. Since

Δ_{r} H = Δ_{r} G + T Δ_{r} S

with

T Δ_{r} S > 0

Δ_{r} H

is less negative than

Δ_{r} G

, so option C is wrong.