Wize High School Grade 12 Chemistry Textbook > Electrochemistry

Galvanic Cells

Galvanic/Voltaic Cells

A galvanic cell constructed of two half cells is shown below.
Before we take a deeper look, let's review what we already know about galvanic cells:
Do galvanic cells have spontaneous or non-spontaneous electron flow? ________
Is the ΔG° positive or negative? ________
According to the equation ΔG° = –nFE°redox, is E°redox positive or negative? ________
Let's take a look at our 2 half reactions from the table again:

Zn2+ (aq) + 2e– → Zn(s) E° = –0.76 V

Cu2+(aq) + 2e– → Cu(s) E° = +0.34 V

In order to get an E°redox that is positive, we needed to flip the Zn(s) equation:

Zn(s) → Zn2+ (aq) + 2 e– E°ox = +0.76 V

Cu2+(aq) + 2e– → Cu(s) E°red = +0.34 V

E°redox = 1.1 V

Note: you might see E°cell referred to as the electromotive force or emf. These mean the same thing.

Now let's label the galvanic cell...

Image illustrating Galvanic/Voltaic Cells

1) Which is the reduction half equation and which is the oxidation half reaction?

2) Using the following "Wize Concept," label the anode and cathode in the above diagram.

3) Show where the ions are moving (into solution/onto electrode)

4) Which electrode is shrinking? Which is growing?

5) Consider the salt bridge. Let's say it's made of KCl. Which half cell would the K+ ions travel to? Which half cell would the Cl– ions travel to?

6) Draw the direction of electron flow.

Analogy: Running out of your last exam! Everyone is running in the same direction and to where they want to go (outside of the school!)

7) Write in the charges (+ or –) for each electrode.

8) Write in the spectator ions (in this case it is SO42–; you might see NO3– in other cases).

These ions are called "spectator" ions because that's all they are doing...spectating!
They don't participate in the actual reaction, but help to balance charges.

In a galvanic cell, oxidation occurs at the:

I don't know

Which of the following is true about a galvanic cell?

Electron flow is non-spontaneous

Only one connection is needed between the two half cells and that is a salt bridge.

Two connections are needed between the two half cells and that is a salt bridge and a wire.

The cations from the salt bridge would need to flow to the anode.

I don't know

Mark Yourself Question

Grab a piece of paper and try this problem yourself.
When you're done, check the "I have answered this question" box below.
View the solution and report whether you got it right or wrong.

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

$Na^+_{(aq)} +e^- \to Na_{(s)} \hspace{40pt} E^o=-2.71V$

$S_2O_{8(aq)}^{2-} +2e^- \to 2SO_{4(aq)}^{2-} \hspace{20pt} E^o=2.01V$

$I_{2(s)}+2e^- \to 2I^-_{(aq)} \hspace{43pt} E^o=0.54V$

$Ni_{(aq)}^{2+} +2e^- \to Ni_{(s)} \hspace{35pt} E^o=-0.23V$

I have answered this question

Spontaneity Rule

We learned that we can calculate Eoredox (Eoredox=Eooxidation+ Eoreduction) and use the equation ΔG=-nFE to figure out spontaneity
In grade 12 there is a quicker way you may be more familiar with called the "spontaneity rule"

Before we take a look at this new rule, let's review what we already learned...

Question: Can solid aluminum and aqueous copper (II) sulphate react?

Find the Eored values in the table:
Al3+(aq) + 3e- --> Al(s) Eored=-1.66V
Cu2+(aq) + 2e- --> Cu(s) Eored=0.34V

Flip the equation with aluminum since Al(s) is supposed to be a reactant:

Al(s) --> Al3+(aq) + 3e- Eoox=+1.66V
Cu2+(aq) + 2e- --> Eored=0.34V

Calculate Eoredox=Eoox + Eored

Eoredox=1.66 + 0.34V

Eoredox=2V

Since Eoredox is positive, we know the reaction is spontaneous and so these will react!

Now, let's use the spontaneity rule to arrive at the same answer:

According to the spontaneity rule, any strong reducing agent + strong oxidizing agent will be able to react spontaneously (so a reaction will occur!)

Determine if the following reactions will occur or not.

Will the reaction occur between aqueous calcium nitrate and solid nickel?

Yes

I don't know

Extra Practice

Electrochemistry: Ksp calculations

Use the following reduction potentials to calculate the Ksp of La(OH)3(s)

\begin{array}{llllll}&La(OH)_{3(s)}&+&3e-&\rightarrow& La_{(s)}&+&3\ OH^-_{(aq)}& &&E^o=-2.90 V \\ &La^{3+}_{(aq)}&+&3e^-&\rightarrow& La_{(s)}&&&&& E^o=-2.379\ V \end{array}

Electrochemistry: Battery

Given the following half cells, what is the maximum voltage of a battery that could be constructed?

\begin{array}{llll}&Li^+_{(aq)}&+&e^{-}&\rightarrow&Li_{(s)}&&E^o=-3.04\ V\\ \\&Ce^{4+}_{(aq)}&+&e^{-}&\rightarrow&Ce^{3+}_{(s)}&&E^o=1.44 \ V \\ \\&Co^{3+}_{(aq)}&+&e^{-}&\rightarrow&Co^{2+}_{(aq)}&&E^o=1.82 \ V \end{array}

A voltaic cell is constructed with an Sn/Sn2+ half-cell and a Zn/Zn2+ half-cell. The zinc electrode is negative.

Draw a diagram of this cell, labeling electrodes with their charges and showing the direction of electron flow in the wire and anion/cation flow in the salt bridge

Electrochemistry: Standard Reduction Potentials

A galvanic cell is constructed from chromium and copper electrodes immersed in aqueous solutions of Cr3+and Cu2+ respectively (half-reactions shown below).

$Cr^{3+}(aq)+3e^-⇌Cr(s)$ $E°_{red}=-0.74V$

$Cu^{2+}(aq)+2e^-⇌Cu(s)$ $E°_{red}=+0.34V$

Electrochemistry: Reduction potentials in a Galvanic Cell

Use the standard reduction potentials below to answer the following question: which metal could be used to create a sacrificial anode for an aluminum pipe?

$\begin{array}{c:c}\rm Reduction\ half-reaction& E° (V)\\ \hline 𝐶𝑎^{2+} (𝑎𝑞)+2 𝑒^−⇌𝐶𝑎 (𝑠)& -2.87\\ \hline 𝑁𝑎^+ (𝑎𝑞)+𝑒^−⇌𝑁𝑎 (𝑠)&-2.71\\ \hline 𝐴𝑙^{3+} (𝑎𝑞)+3 𝑒^−⇌𝐴𝑙(𝑠) &-1.66\\ \hline 𝑀𝑛^{2+} (𝑎𝑞)+2 𝑒^−⇌𝑀𝑛 (𝑠)&-1.18\\ \hline 𝐶𝑢^{2+} (𝑎𝑞)+2 𝑒^− ⇌𝐶𝑢 (𝑠) &+0.15\\ \hline 𝐴𝑔^+ (𝑎𝑞)+𝑒^− ⇌𝐴𝑔 (𝑠)&+0.80\end{array}$

Choose the INCORRECT statement

A voltaic cell is constructed with an Sn/Sn2+ half-cell and a Zn/Zn2+ half-cell. The zinc electrode is negative.

Write a balanced overall reaction for this cell
Draw a diagram of this cell, labeling electrodes with their charges and showing the direction of electron flow in the wire and anion/cation flow in the salt bridge

Electrochemistry: Galvanic Cells

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

$Na^+_{(aq)} +e^- \to Na_{(s)} \hspace{40pt} E^o=-2.71V$

$S_2O_{8(aq)}^{2-} +2e^- \to 2SO_{4(aq)}^{2-} \hspace{20pt} E^o=2.01V$

Electrochemistry: Galvanic Cell

In a zinc-lead cell the reaction is:

$Pb^{2+}\left(aq\right)+Zn\left(s\right)\to Pb\left(s\right)+Zn^{2+}\left(aq\right)\ \ \ \ \ \ \ E\degree=0.637V$

Which of the following statements about this cell is FALSE?

Electrochemistry: Galvanic Cells

In a galvanic cell, oxidation occurs at the:

Practice: Galvanic Cells

Galvanic Cell Practice

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

$Na^+_{(aq)} +e^- \to Na_{(s)} \hspace{40pt} E^o=-2.71V$

Practice: Galvanic Cells

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

$Na^+_{(aq)} +e^- \to Na_{(s)} \hspace{40pt} E^o=-2.71V$

$S_2O_{8(aq)}^{2-} +2e^- \to 2SO_{4(aq)}^{2-} \hspace{20pt} E^o=2.01V$

Practice: Galvanic Cells

Galvanic Cell Practice

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

$Na^+_{(aq)} +e^- \to Na_{(s)} \hspace{40pt} E^o=-2.71V$

Galvanic Cells

Create a free account to get started

Galvanic/Voltaic Cells

Now let's label the galvanic cell...

1) Which is the reduction half equation and which is the oxidation half reaction?

2) Using the following "Wize Concept," label the anode and cathode in the above diagram.

3) Show where the ions are moving (into solution/onto electrode)

4) Which electrode is shrinking? Which is growing?

5) Consider the salt bridge. Let's say it's made of KCl. Which half cell would the K+ ions travel to? Which half cell would the Cl– ions travel to?

6) Draw the direction of electron flow.

7) Write in the charges (+ or –) for each electrode.

8) Write in the spectator ions (in this case it is SO42–; you might see NO3– in other cases).

Create a free account to get started

Create a free account to get started

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

Create a free account to get started

Create a free account to get started

Create a free account to get started

Spontaneity Rule

Create a free account to get started

Extra Practice

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

Galvanic Cell Practice

Construct a galvanic cell with the highest voltage given the following half reactions. Determine the voltage produced and express it in standard cell notation.

Galvanic Cell Practice