Chemical Equilibrium

Question 1

For a system of variable composition, the fundamental equation for the Gibbs energy is ___

At constant T and P, the equation becomes ___

Answer 1

dG = -SdT + VdP + Σ(ui dni)

dG = Σ(ui dni)

Question 2

The chemical potential for a component in a mixture is ___

Answer 2

ui = (dG/dni) T, P, nj

Question 3

For a reaction with initial amount of components, the change in the amount of all components can be characterized by _____ aka ___

Answer 3

extent of reaction aka advancement of reaction

Question 4

Formula for extent of reaction

Answer 4

ξ = (ni - ni°)/vi

Question 5

What is vi in the extent of reaction formula?

Answer 5

stoichiometric coefficient of the component in the balanced chemical equation

Question 6

How to calculate the change in the amount of one component?

Answer 6

ni - ni° = vi ξ

Question 7

Sign of vi is ____ for reactants and ____ for products.

What does it imply?

Answer 7

negative for reactants
positive for products

Forward reaction, decrease in amount of reactants and increase in amount of products
and vv.

Question 8

Reversible reactions will proceed to a direction that ____

Answer 8

will minimize the total Gibbs energy of the system

Question 9

Describe the plot of Gibbs energy against extent of reaction

Answer 9

U-shaped where the minimum is said to be in equilibrium (dG/dξ = 0)

The left side is dG/dξ = negative
The right side is dG/dξ = positive

Question 10

Slope of G vs ξ plot

Answer 10

reaction Gibbs energy ∆Gr = (dG/dξ) at constant T, P

Question 11

Equilibrium condition in terms of (1) ξ and (2) μ

Answer 11

∆Gr = (dG/dξ) at cons. T,P = 0
∆Gr = Σ vi μi = 0

Question 12

∆Gr in terms of standard rxn Gibbs energy

Answer 12

∆Gr = ∆Gr° + RT ln ((Pc^c Pd^d)/(Pa^a Pb^b))

∆Gr = ∆Gr° + RT ln Q

Question 13

For heterogeneous equilibria, the activity of pure solids and pure liquids is equal to __ because

Answer 13

one
their chemical potentials are essentially constant

Question 14

Equilibrium constant K = ?

Answer 14

exp (-∆Gr°/RT)

Question 15

van’t Hoff equation and its limitation

Answer 15

ln (K T2/K T1) = - (∆Hr°/R)(1/T2 - 1/T1)

Large error for large difference in temperature

Question 16

(T/F): Extent of reaction depends in the initial amount of components

Answer 16

True using K expression

Question 17

Le Châtelier principle

Answer 17

a system at equilibrium that is subjected to external stress will shift to counteract the stress

change of extent if reaction with T or P

Question 18

Direction of rxn when there is a positive change in ξ

Answer 18

forward

Question 19

Direction of rxn when there is a negative change in ξ

Answer 19

reverse

Question 20

(dξ/dP) cons. T = ?

Answer 20

(dξ/dP)T = -∆V / G’’ = -∆nRT/PG’’

Question 21

what will happen if rxn leads to increase in volume (+∆V)?

Answer 21

increase in pressure makes the reverse rxn to occur since (dξ/dP)T is negative

Question 22

(T/F): For condensed phase systems, change in volume is negligible; the effect of pressure will tell the shift of reaction

Answer 22

False. Effect of pressure on extent of rxn is not significant for rxns that do not involve gaseous components

Question 23

For a system at equilibrium with pressure being constant,

(dξ/dT)P = ?

Answer 23

(dξ/dT)P = ∆H/TG’’

Question 24

If the rxn is endothermic (+∆H), increasing temperature will ___

Answer 24

favor the forward reaction

Question 25

If the rxn is exothermic (-∆H), increasing temperature will ___

Answer 25

favor the reverse reaction

Question 26

Reaction direction when ∆ξ is negative

Answer 26

reverse