Homework

# Electrochemistry and Electrolysis

## Chapter 19: 5-8 Homework

#### Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 18: Sections 5 to 8.

##### Study Notes
• 19.5 The energy associated with the difference in electric potential equals the work necessary to move charges against the electric force arising from differences in field strength, just as moving a mass uphill requires work to overcome gravitational force arising from differences in distance from the center of mass.

The half-cell voltages listed in the previous section are determined under standard conditions. We can consider electric potentials using the Nernst equation for temperatures and concentrations when the latter are expressed in the reaction quotient Q.

• 19.6 The maximum work that can be done by the reactions of the half-cells depends on the energy content of the cell, measured in terms of its charge and potential.
• 19.7 Electrolysis is the use of electrical current to supply the energy for chemical change. This process is the reverse of that in a voltaic cell, which uses chemical reactions to produce current.
• 19.8 Electrolysis reactions allow us to determine the number of electrons exchanged from the current produced. This is an important method for determining the mole relationships in a reaction to verify a molecular formula (mass relationships can only produce an empirical formula).

#### Key Formula

PrincipleFormulaNotes
Work wmax = nFE E: cell potential
nF: amount of electric charge transfered
Nernst Equation E: actual potential at temperature T
E°: potential at STP
n: number of moles of electrons transfered
F: total charge per mole electrons
R: gas constant
T: Temperature (K)
Q: reaction quotient
Nernst at STP (298.15K) Constants R, T, F calculated
Free Energy (STP) ΔrG° = -nFE° G°: Gibbs free energy for reduction half-reaction
E°: electric potential change for reduction half-reaction
Free Energy and Nernst at Equilibrium E = 0 at equilibrium
Electron count i: current (Amps)
C: charge
t: time

Read the following weblecture before chat: Electrochemistry and Thermodynamics

#### Videos for Chapter 19: Principles of Chemical Reactivity: Entropy and Free Energy

Review the Videos at Thinkwell Video Lessons.

• Under "ELECTROCHEMISTRY"
• Galvanic Cells
• The Nernst Equation
• Electrochemical Determinants of Equilibria
• Batteries
• Batteries
• Electrolysis and Electrolytic Cells
• Electrolytic Cells
• The Stoichiometry of Electrolysis

Use the Electrolysis Experiment simulation to run a virtual electrolysis experiment.

• Read the Overview and Learning Outcomes, then click on "Experiment".
• Select the option to run the Experiment.
• Choose your own metals for the positive and negative terminals. Record thee masses of the electrodes.
• Choose a solution from the dropdown menu.
• Set the current to 1.00 amp.
• Set the timer to 5:00 minutes (300 seconds).
• Turn the ammeter on to run the experiment.
• Which metal is the anode? Which is the cathode?
• What is the initial mass of the anode? Of the cathode?
• What are the final masses of each electrode?
• Which increased in mass? Which decreased in mass?
• Which way do the electrons flow?
• Click the rerun button on the ammeter to repeat the experiment with these electrodes at least three more times
• 2.00 amps and 5 minutes
• 3.00 amps and 5 minutes
• 2.00 amps and 10 minutes
• For each run
• Record the starting masses of the anodes for each run.
• Record the final masses of the anodes for each run.
• How does changing the time affect the mass change?
• How does changing the current affect the mass change?
• Repeat the experiment with different electrodes.

#### Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

#### Chapter Quiz

• Required: Complete the Mastery exercise with a passing score of 85% or better.
• Go to the Moodle and take the quiz for this chapter.

#### (Aligns to) AP LAB #16 GUIDED INQUIRY — — Building an Electrochemical cell — Phase III

Use your batteries (or commercial batteries) to observe the results of electrolysis on common molecules and rank results. Write and post your formal report.

Resources:

• AP2009 20 Determination of Electrochemical Series
• AP2009 21 Measurements using electrochemical cells and electroplating
• IGHCE Lab 16.1 OR HSCKM X-1 Produce Hydrogen and Oxygen by Electrolysis of Water
• IGHCE Lab 16.2 OR HSCKM X-2 Observe the Electrochemical Oxidation of Iron
• IGHCE Lab 16.3 OR HSCKM X-3 Measure Electrode Potentials
• IGHCE Lab 16.4 Observe Energy Transformation
• IGHCE Lab 16.5 OR HSCKM X-4 Build a Voltaic Cell
• IGHCE Lab 16.6 Build a Battery