voltaic cells in non-standard conditions, how does concentration of solm's effect the value of Ecell. I understand that as concentration increases so does the E-cell value but why?
The half cell is
E = Eo - 0.0592 log Q where Q stands for K at equilibrium and K = (ox)/(red).
Therefore, as the concentration of the oxidized materials and/or the reduced materials changes, so does Q and that changes Eo from non-standard conditions. The 0.0592 constant is made up of other constants, 2.303 RT/F
To understand why the concentration of solutes affects the value of Ecell in voltaic cells, let's break down the components of the Nernst equation that you mentioned.
The Nernst equation relates the standard electrode potential (E°) of a half-cell reaction to the actual cell potential (E) under non-standard conditions. It is given by:
E = E° - (0.0592 / n) log(Q)
Where:
- E is the actual cell potential
- E° is the standard electrode potential
- n is the number of electrons transferred in the balanced redox equation
- Q is the reaction quotient
The reaction quotient, Q, is the ratio of the concentrations of products and reactants at any given point during the reaction. For a half-cell reaction, Q is determined by the concentrations of the oxidized (ox) and reduced (red) species, represented as [ox] and [red], respectively. So, Q = [ox] / [red].
Now, let's consider how changes in concentration affect the value of Ecell. According to the Nernst equation, increasing the concentration of the oxidized species or decreasing the concentration of the reduced species will lead to a higher value of Q. This, in turn, will result in a lower value of the log(Q) term in the equation.
Since the Nernst equation has a negative sign in front of the log(Q) term, a lower value of log(Q) will cause the overall term to become more positive. As a result, the actual cell potential (E) will increase relative to the standard electrode potential (E°). In other words, increasing the concentration of the oxidized species or decreasing the concentration of the reduced species will make the cell potential more positive (or less negative) compared to its standard value.
Conversely, decreasing the concentration of the oxidized species or increasing the concentration of the reduced species will lead to a lower value of Q, causing the overall E term to become more negative. Consequently, the actual cell potential (E) will decrease relative to the standard electrode potential (E°), making it more negative (or less positive).
In summary, changes in concentration affect the value of Ecell because they modify the reaction quotient (Q) in the Nernst equation, which then adjusts the relationship between the actual cell potential (E) and the standard electrode potential (E°).