Equations
What is the equation for calculating E0cell from a standard reduction potentials chart?
E0cell = E0red + E0ox
(E0cell = E0cathode - E0anode)
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)
a) Oxidation is ____ of electrons & ___ in oxidation #
b) Reduction is ____ of electrons & ____ in oxidation #
a) loss, increase
b) gain, decrease
All reactants in a reduction chart are?
oxidizing agents
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
What is (delta)Suniv = to?
(delta)Suniv = (delta)Ssys + (delta)Ssurr
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
In a voltaic cell & electrolytic cell oxidation and reduction take place at which electrodes?
oxidation at anode (ox-an)
Reduction at cathode (red cat)
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
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
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. Teqbm = (delta)H/(delta)S
Phase changes represent what equation?
Phase changes are equilibrium processes. Which also means we can calculate Teqbm.
Teqbm = (delta)H/(delta)S
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
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
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)
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
What are the signs of (delta)H & (delta)S that make a rxn spontaneous at all temps?
(delta)H = - (negative)
(delta)S = + (positive)
Answer the following about concentration cells:
a) Which value needs to be smaller, [M]Anode or [M]Cathode in order to produce a positive Ecell value (spont. process)?
b) What will the Nernst equation look like for a concentration cell?
a) [M]Anode < [M]Cathode
b) Ecell = (-0.0592/n)log([M]A/[M]C)
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"
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
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) Ecell = E0cell - (RTlnQ/nF) (any temp)
Ecell = E0cell - (0.0592logQ/n) (@ 250C)
b) (delta)G0 = -nFE0cell (standard)
(delta)G = -nFEcell (non-standard)
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
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)
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)
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- E0red = -0.83
Oxidation:
2H2O(l) --> O2(g) + 4e + 4H+ E0ox = -1.23