For a voltaic cell that's made with zinc and copper {reaction equation: Zn(s) + Cu2+(aq) ---> Cu(s) + Zn2+(aq)}, if the concentration of zinc nitrate increases, would the cell voltage decrease, or would it increase? Thanks!
According to the Nernst equation, the cell voltage of a voltaic cell depends on the concentration of the participating species. In the given reaction, the concentration of zinc nitrate affects the concentration of Zn2+ ions, which is on the reactant side of the cell reaction.
From the Nernst equation:
Ecell = E°cell - (RT/nF) * ln Q
Where:
Ecell is the cell potential (voltage)
E°cell is the standard cell potential
R is the gas constant
T is the temperature
n is the number of electrons transferred
F is Faraday's constant
Q is the reaction quotient, Q = [Zn2+]/[Cu2+]
As the concentration of zinc nitrate increases, the concentration of Zn2+ ions would increase, leading to an increase in the reaction quotient (Q).
Since Q is in the denominator of the natural logarithm, an increase in Q will result in a decrease in the overall value of the logarithm.
Therefore, according to the Nernst equation, as the concentration of zinc nitrate increases, the cell voltage will decrease.
To determine how the concentration of zinc nitrate affects the cell voltage of a voltaic cell, it is important to understand the concept of cell potentials.
The cell potential, also known as cell voltage or electromotive force (EMF), is a measure of the electric potential difference between the two half-cells in a voltaic cell. It indicates the driving force for the flow of electrons from the oxidized species to the reduced species in the cell.
In this particular voltaic cell that you mentioned, the half-reactions are:
At the anode (oxidation half-reaction): Zn(s) → Zn2+(aq) + 2e^-
At the cathode (reduction half-reaction): Cu2+(aq) + 2e^- → Cu(s)
The overall cell reaction (combining both half-reactions) is:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
The cell potential (Ecell) for this reaction can be determined using the Nernst equation:
Ecell = E°cell - (0.0592/n) * log(Q)
Where:
Ecell is the cell potential
E°cell is the standard cell potential
n is the number of electrons transferred in the balanced cell reaction
Q is the reaction quotient, which is the ratio of the product concentrations to reactant concentrations, each raised to the power of their stoichiometric coefficients.
Now, let's consider how the concentration of zinc nitrate affects the cell potential:
If the concentration of Zn2+(aq) (which comes from zinc nitrate) increases, the concentration term (Q) for Zn2+(aq) in the Nernst equation will increase. As a result, the log(Q) term will become more positive, causing a decrease in cell potential (Ecell).
However, it's important to note that this is true only if the concentration of Cu2+(aq) remains constant. If the concentration of Cu2+(aq) changes as well, it will have an additional effect on Ecell.
In summary, when the concentration of zinc nitrate (and thus Zn2+(aq)) increases while Cu2+(aq) concentration is held constant, the cell voltage of the voltaic cell will decrease.