Toni L4

Question 1

Define standard state for a solid or liquid

Answer 1

For a solid or liquid the standard state is the pure solid or liquid at 1 bar pressure (10^5 Nm-2)

Question 2

Define standard state for a solution

Answer 2

For a solution the standard state of the solute is a solution of concentration 1 mol kg-1 at Q bar pressure and ideal behaviour

Question 3

Describe standard temperature

Answer 3

There is no standard temperature. Standard ambient temperature means standard room temperature = 298K is not standard temperature and has nothing to do with the standard state

Question 4

How do we calculate the activity of species A

Answer 4

{A} = yA x [A]/c0
yA -Activity coefficient of A (corrects for non-ideal behavior)
[A] - Molar concentration of A (mol/L or M)
C0 - Standard concentration (usually 1 mol/L) to make the activity dimensionless

Question 5

Why are activity and activity coefficients dimensionless

Answer 5

Acitivity and activity coefficients are dimensionless because of the factor c0 in the denominator

Question 6

What do the terms mean in the following equation ti calculate chemical potential
μ =μϴ + RTln[A] + RTlnγA

Answer 6

μ - chemical potential
μϴ - standard chemical potential
RTln[A] - standard entropy of mixing term
RTlnγA - deviation from ideality for a real solution - change in free energy per mole of A from hypothetical solution to real solution

Question 7

What is the following equation used for and what does each term mean
Log10γi = -0.51zi^2 √I

Answer 7

Way of calculating the contribution of the activity coefficient
-0.51 specific to water at 298k
z charge in the ion
I ionic strength of the entire solution

Question 8

To calculate the ionic strength we use the following equation but what does each letter represent
I = 1/2 ∑(cj/cϴ)zj^2

Answer 8

cj is the concentration of ion j
cϴ Standard concentration
Zj charge number on ion j

Question 9

Describe the relationship between activity coefficients and ionic strength

Answer 9

Activity coefficients tend to 1 as the ionic strength tends to zero.

Question 10

What do activity coefficients depend strongly on

Answer 10

Activity coefficients depend strongly on the magnitude of the charge on the ion

Question 11

What is the free energy of reaction equation

Answer 11

ΔG = ΔGϴ + RTln {D}d{C}c/{B}b{A}a

Question 12

Describe how we calculate ΔGϴ

Answer 12

At equilibrium ΔG =0 so
ΔGϴ = -RTlnK
K is related to the standard free energy of reaction

Question 13

Describe sign convention for electrode potentials

Answer 13

By convention the right hand electrode is connected to the positive side of the voltmeter
E=Er-El

Question 14

What is the standard hydrogen electrode

Answer 14

The half cell Pt/H+
corresponds to the half reaction
with everything under standard conditions, is the standard
hydrogen electrode and has Eϴ
SHE = 0 by convention.