Our final unit contains two topics, electrochemistry and molecular orbitals.
Earlier in this course, you learned about oxidation-reduction reactions and that they involved a flow of electrons from one reactant to another. In electrochemistry, this flow of electrons is carried out via an electrical circuit or connection, allowing the redox reaction to occur without the reactants being directly mixed or contacted. This concept, and a few of the many applications and technologies developed as a result, will be studied.
In CHEM 151 or you first semester general chemistry course, you likely learned about Lewis dot structures, their connection to molecular shape or geometry, and hybridization. This is also part of a theory of covalent bonding called valence bond theory. Molecular orbital theory is another theory of bonding that takes a different approach – that the orbitals of each atom combine to make new orbitals for the entire molecule–to bonding and is more useful for explaining some phenomena than the valence bond theory
Unit 4 Objectives
Electrochemistry
- Define and identify oxidation and reduction – Review from Unit 3
- Identify oxidation-reduction (redox) reactions – Review from Unit 3
- Assign oxidation states to the elements in a compound or ion. – Review from Unit 3
- Identify oxidizing and reducing agents. – Review from Unit 3
- Diagram and describe and explain voltaic (or galvanic) and electrolytic cells: indicate the cathode, anode, salt bridge, direction of flow of electrons, direction of migration of ions and the half-cell reaction involved at each electrode.
- Write voltaic cells using standard line notation.
- Define cell potential and explain how it is measured.
- Define standard reduction potential.
- Explain how standard reduction potentials are assigned in terms of the standard hydrogen electrode.
- Using tabulated standard reduction potential calculate the standard cell potential (standard EMF) of a galvanic cell and predict whether the reaction is spontaneous.
- Given the components of the electrodes and observations on what happens at the electrodes in a voltaic cell, write the balanced oxidation and reduction half reactions, write the balanced overall spontaneous reaction, and calculate the cell voltage
- Using standard reduction potentials predict the strength of various oxidizing and reducing agents.
- Explain the relationship between the maximum cell potential and the free energy difference between cell reactants and products.
- Know and be able to use the equations that relate ΔG°, K and E° for cell reactions.
- Explain the basis for concentration cells.
- Qualitatively predict the effect of concentration and gas pressure on cell potential.
- Use the Nernst equation to calculate the EMF under nonstandard conditions or to calculate a concentration of reactant or product required to give a certain voltage.
- Explain with the aid of the balanced equation the operation of fuel cells and of the lead-acid, alkaline, the nickel-cadmium, nickel-metal hydride, and lithium-ion batteries.
- Distinguish between batteries and fuel cells.
- Explain the electrochemical nature of corrosion and describe some methods of preventing it.
- Explain the difference in product at each electrode for molten salts compared to aqueous solutions of the salt.
- Using standard reduction potentials predict the most likely product at each electrode in the electrolysis of aqueous solutions and write the equation for the reaction.
- Given two of the three following variables: time, current or amount of substances reacting in an electrolytic cell, calculate the third variable. Amount can be indicated by grams, volume, moles, concentration, pH, pOH, molar mass, or oxidation state
- Explain how electrolysis can be used in the application of metal plating.
Molecular Orbitals
- Explain the essential features of the molecular orbital theory.
- Explain the relationship between bonding and antibonding molecular orbitals, both in terms of energy compared to the corresponding atomic orbitals and where electron density is concentrated relative to the nuclei.
- Given a molecular orbital diagram for the diatomic molecule or ion built from elements of the first or second period, predict the placement of electrons, the bond order and the number of unpaired electrons. Also, determine whether the molecule is paramagnetic or diamagnetic.
Unit 4 Topics
Study these in order:
