Exam #3 Review

Equations

100

What is the equation for calculating E⁰_cell from a standard reduction potentials chart?

E⁰_cell = E⁰_red + E⁰_ox 

(E⁰_cell = E⁰_cathode - E⁰_anode) 

200

What is (delta)S_univ = to? 

(delta)S_univ = (delta)S_sys + (delta)S_surr

300

1. What is the equation for Gibbs Free Energy Change? 

2. What is the equation for calculating the equilibrium temp? 

1. (delta)G = (delta)H - T(delta)S

2. T_eqbm = (delta)H/(delta)S

400

1. What is the equation that relates (delta)G under standard and non-standard conditions? 

2. What is the equation when it is at equilibrium? 

1. (delta)G = (delta)G⁰ + RTlnQ

2. (delta)G⁰ = -RTlnK

500

a) Nernst equation at any temp and then at 25⁰C? 

b) Bonus! - What are the equations for the Gibbs Free energy change under standard & non-standard conditions for redox reactions? 

a) E_cell = E⁰_cell - (RTlnQ/nF) (any temp) 

E_cell = E⁰_cell - (0.0592logQ/n) (@ 25⁰C)

b) (delta)G⁰ = -nFE⁰_cell (standard) 

(delta)G = -nFE_cell (non-standard)

Thermo Basics

100

For any spontaneous reaction: 

a) (delta)S must be?

b) (delta)G must be?

(answer with positive or negative) 

a) (delta)S > 0 (positive) 

b) (delta)G < 0 (negative) 

200

If you were to solve for the value of (delta)H & (delta)S for a certain rxn and were only given a list of values for each component of the rxn, what method/equation would you use to solve for them? 

Sum of products * coeff - Sum of reactants * coeff

300

Phase changes represent what equation? 

Phase changes are equilibrium processes. Which also means we can calculate T_eqbm.

T_eqbm = (delta)H/(delta)S

400

What are the signs of (delta)H & (delta)S that make a rxn spontaneous at all temps? 

(delta)H = - (negative) 

(delta)S = + (positive) 

500

Are the following scenarios examples of an increase in entropy? 

a) CO(g) + O2(g) --> CO2(g) + O(g) 

b) MgCO3(s) --> MgO(g) + CO2(g) 

c) Iron Melting 

a) no, 2moles of gas --> 2 moles of gas

b) Yes, solid to gas or increased number of particles 

c) Yes, solid to liquid or low temp to high temp 

Electrochem Basics

100

a) Oxidation is ____ of electrons & ___ in oxidation #

b) Reduction is ____ of electrons & ____ in oxidation #

a) loss, increase 

b) gain, decrease 

200

In a voltaic cell & electrolytic cell oxidation and reduction take place at which electrodes? 

oxidation at anode (ox-an) 

Reduction at cathode (red cat) 

300

Answer the following about line notation: 

a) By convention what is written on the left and right side? 

b) If there is no metal on a side what do we do?

c) Why would we use a comma? 

a) left - anode(ox.) & right - cathode(red.)

b) we add Pt(s) or graphite to the end of the side lacking a metal 

c) to separate substances in the same phase

*if concentrations are given include then in the notation in () or else it is assumed to be 1M 

400

Answer the following about concentration cells: 

a) Which value needs to be smaller, [M]_Anode or [M]_Cathode in order to produce a positive E_cell value (spont. process)? 

b) What will the Nernst equation look like for a concentration cell? 

a) [M]_Anode < [M]_Cathode

b) E_cell = (-0.0592/n)log([M]_A/[M]_C)

500

Voltaic/Galvanic/Daniel Cells: 

a) electrons flow from what to what? 

b) Anode is a (pos/neg) electrode & Cathode is a (pos/neg) electrode? 

a) Anode ---> Cathode 

b) negative b/c electrons are produced (ox. 1/2 rxn), positive b/c electrons are consumed (reduction 1/2 rxn) 

Reduction Chart Components

100

All reactants in a reduction chart are? 

oxidizing agents 

200

Match the letter to the bank: 

1. The more positive the E value, the stronger the ____?

2. The more negative the E value, the stronger the ____? 

a) Oxidizing Agent

b) Reducing Agent 

1. a) Oxidizing agent 

2. b) Reducing agent 

300

With using the terms S.O.A., W.O.A., S.R.A., W.R.A write our how a spont. redox reaction will look like. 

SOA + SRA ---> WOA + WRA 

400

Will an oxidizing agent react with a reducing agent above it on the reduction potentials chart in order to produce a spont. rxn? 

No, "a spont. rxn will occur between an O.A. and any R.A. that lies BELOW it" 

500

Label which is the oxidation or reduction half rxn: 

a) Sn2+ + 2e --> Sn(s) E = -0.14V

b) Ag+ + e --> Ag(s)    E = 0.80V

a) oxidation

b) reduction 

(we want a positive E value, so we flip rxn a in order to obtain this) 

Molten/Aqueous Salts & Electroplating

100

What is the very first step when we are dealing with Molten or Aqueous salts?

Ionization step! Where we break up our compund into its respective ions 

200

In the electrolysis of molten salts the cation will be (reduced/oxidized) and the anion will be (reduced/oxidized)? 

Cation will be reduced and anion will be oxidized.

*(cation --> cathode & anion --> anode) 

*we use the same logic for aqueous salts but there are a few exceptions, refer to CW 17.5-7 pg3 

300

a) 1 Faraday's constant = _____ C?

b) What is the equation to calculate Coulombs (C)?

a) 96,500 C

b) C = Current (amps, A) x Time (seconds) 

400

How do we predict products for aqueous salts? 

The oxidation or reduction 1/2 rxn with the most positive E⁰ value is favored, therefore that is how we predict which products are produced. 

*Products for competing rxn's are H₂(g) for reduction & O₂(g) for oxidation 

500

What are the 2 competing reactions for when we are dealing with aqueous salts? What are their corresponding E values? 

Reduction: 

2H2O(l) + 2e --> H2(g) + 2OH-   E⁰_red = -0.83

Oxidation: 

2H2O(l) --> O2(g) + 4e + 4H+    E⁰_ox = -1.23