electrochemistry

Electric current (I):

What does it measure?

What are Units?

What is the formula?

Flow of electric charge per unit time

Amperes (A)

I=Q/T where time is seconds and Q is charge

Charge (Q):

What does it measure?

Units?

Formula?

Total quantity of electrons flowing

Coulombs

Q= I x T

Potential (Voltage, E)

What does it measure?

What are the units and what do they stand for?

Driving force pushing electrons

Volts (V) which is J/C (Joules/Coulombs)

What is the amount of charge that passes per unit time is called?

Current

Charge is measured in?

Coulombs (C)

The diving force for electrons is measured by?

Potential (voltage, e)

Current is measured in?

Amperes (A)

Potential is measured in?

Volts (V) (J/C)

Rank the species by oxidizing strength (best to poorest):

Br2 (+1.07 V)

Fe3+ (+0.77V)

Zn2+ (-0.76V)

K+(2.93V)

Br2, Fe3+, Zn2+ and K+

Calculate (reduction potential) Ecell given Cu(s)+Ag(aq)→Cu2++Ag(s) where cu is 0.52 and ag is 0.80

0.80-0.52=0.28V

When oxidizing an element, is the oxidizer going to have a bigger or smaller voltage? Why?

The oxidizer has a bigger voltage because it is the reduced element in a reaction.

Given Fe to Fe2+ is -0.44, which can oxidize it?

Ag: +0.80

Mg: -0.65

Ag because its bigger and it is the oxidizing agent (the one reduced AKA the cathode)

What is the standard free energy charge (delta G) or delta Grxn

-(n)(96485)(Ecell) or -nFEcell

Describe the steps of finding the delta G of a third half reaction given the Ecell of two half reactions

1. Add the half cell potentials together (with respect to their coefficients) ex: (-0.407) 2(-0.913)

2. Divide by the number of electrons (e-) of the THIRD half reaction that you are solving for

Find the reduction potential of the third half reaction given:

Cr3++e−→Cr2+
E1∘=−0.407 V

Cr2++2e−→Cr(s)
E2∘=−0.913 V

Target:
Cr3++3e−→Cr(s)
E3∘=?

-0.744

If you are given four half reactions instead of two, what do you do?

1. Find the two that have the same end game as the one you are solving for (X(s) OR X²+)

2. Reverse the sign of the smaller reaction

3. Solve like you would by getting the Delta G (added ecell potentials of the two half reactions / e- of the third half reaction that you are SOLVING FOR)

What does it mean for the Ecell to be spontaneous or non spontaneous

Ecell > 0 → spontaneous AND Ecell < 0 → non-spontaneous

What is the Nernst equation? What is it used to calculate?

The Nernst equation is used to calculate cell potential (V) in a non-standard Ecell conditions (when given M in a reaction)

What is the Nernst equation given a standard temperature of 25 degrees celsius/298K

Ecell (standard) - 0.0592/n log(Q) where Q is Manod/Mcathod where the COEFFICIENTS are the EXPONENTS when calculating Q

What is the Nernst equation given a non standard temperature?

Ecell (standard) - RT/nF ln(Q) where Q is Mano/Mcatho where the COEFFICIENTS are the EXPONENTS when calculating Q

What happens to E(standard) and E(nonstandard) when coefficients are doubled?

Unchanged

What happens to Q and lnQ?

Q²

2InQ

What happens to n = e- = electrons

Also doubles so 1 → 2

How do you solve for K?

InK = nFEcell / RT

To derive K from Ink in previous answer, you take the answer to the power of e (e^#)

How do you calculate how much is plated out of an element?

1. Solve for current (Q) = A x T (seconds)

2. Convert Charge (Q) to moles of e- : Q / F

3. Convert moles of e- to actual moles by dividing moles of e- by the amount of electrons in equation: moles of e- / e-

4. now you have the actual moles, multiply that by the molar mass of given element