The Nernst Equation and Cells Away from Standard Conditions · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading a cell away from standard conditions

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. How do you build Q for a cell reaction?

    • Reactants over products with no powers
    • Products over reactants, each raised to its stoichiometric power
    • Molar masses over charges, each times n

  2. What is the Nernst equation for a cell potential E?

    • E equals E standard minus R T over n F times ln Q
    • E equals E standard plus n F over R T times Q
    • E equals R T over F times Q minus E standard

  3. Both electrodes use the same metal but the ion amounts differ on the two sides and a voltage appears. What is this cell?

    • A dry cell at standard state
    • A cell at equilibrium
    • A concentration cell

  4. E standard for a cell is positive. What does that say about K?

    • K sits below 1 and reactants dominate
    • K sits above 1 and products dominate
    • K equals 1 and E stays zero

  5. In a concentration cell, which way does each half cell run?

    • Oxidation in the dilute half cell, reduction in the concentrated one
    • Reduction in the dilute half cell, oxidation in the concentrated one
    • Oxidation in both half cells until Q equals zero

  6. Concentrations work in Q only when the solution is dilute.

    Circle one:   True   False

  7. A running cell shows its voltage fading toward zero. What does that say about Q?

    • Q is approaching K as the cell nears equilibrium
    • Q has drifted far from K toward zero
    • Q now holds activities instead of concentrations

  8. Two cells share the same concentration ratio, but one moves one electron and the other moves two. How do their voltages compare?

    • Both give the same voltage
    • The two electron cell gives the larger voltage
    • The two electron cell gives the smaller voltage
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading a cell away from standard conditions W1-mt_yqmRqDaadR-s1

  1. Products over reactants, each raised to its stoichiometric power · You write Q from the balanced reaction with powers matching coefficients.
  2. E equals E standard minus R T over n F times ln Q · The log term corrects E standard for the actual composition.
  3. A concentration cell · Same chemistry means E standard is zero, and the voltage comes from differing concentrations.
  4. K sits above 1 and products dominate · Positive E standard means K sits above 1, so products dominate.
  5. Oxidation in the dilute half cell, reduction in the concentrated one · The cell evens the two sides out, so dilute dissolves and concentrated plates out.
  6. True · In dilute solution activities match concentrations, but concentrated brines need activities.
  7. Q is approaching K as the cell nears equilibrium · When Q meets K, the log term cancels E standard and E falls to zero.
  8. The two electron cell gives the smaller voltage · Free energy spreads across more charge, so more electrons means a smaller voltage.
Worksheet · LightMySky