Quiz | Chemical Thermodynamics

1

Which of the following statements best describes the Second Law of Thermodynamics?

The energy of the universe is constant

Energy can neither be created nor destroyed

The total entropy of an isolated system can never decrease over time

At absolute zero, the entropy of a perfect crystal is considered to be zero

Second Law of Thermodynamics: the total entropy of an isolated system can never decrease over time and is constant if all processes are reversible ⇒ the entropy change is never negative: ΔSsystem + ΔSsurrounding ≥ 0

Law of Thermodynamics
2

What is the expression of the Gibbs energy change?

ΔGrxn = ΔHrxn + TΔSrxn

ΔGrxn = ΔHrxn - TΔSrxn

ΔGrxn = ΔHrxn - RTΔSrxn

ΔGrxn = ΔHrxn/T + ΔSrxn

Gibbs Energy Change and Spontaneity of Reactions
3

Which of the following criteria for reaction spontaneity is incorrect?

ΔGrxn = 0: reaction is at equilibrium

ΔGrxn < 0: reaction is spontaneous and additional products can form

Q < K: reaction proceeds spontaneously from right to left

None of the above

ΔGrxn = RT ln QK

Gibbs criteria for reaction spontaneity:
If Q < K  ⇔  ΔGrxn < 0: reaction proceeds spontaneously from left to right
If Q > K  ⇔  ΔGrxn > 0: reaction proceeds spontaneously from right to left
If Q = K  ⇔  ΔGrxn = 0: reaction is at equilibrium

Gibbs Energy Change and Spontaneity of Reactions Gibbs Energy Change and Reaction Quotient
4

Which of the following statements is always true when a reversible chemical reaction has attained equilibrium?

The Gibbs free energy of the system reaches a minimum

All reactants have been converted to products

The forward reaction dominates over the reverse reaction

The reaction quotient equal to 0

Gibbs Energy Change and Spontaneity of Reactions Gibbs Energy Change and Reaction Quotient
5

What is the relationship between the equilibrium constant K and the temperature T?

ln K and T are proportional

ln K and -T are proportional

K and ln T are proportional

ln K and 1/T are proportional

ln K = - ∆H0rxnRT + ∆S0rxnR ⇒ a plot of ln K versus 1T is linear (ln K and 1T are proportional)

Van’t Hoff and Clapeyron-Clausius Equations
6

When does the entropy usually increase?

A molecule is broken into 2 or more molecules

A solid turns into a liquid

A liquid turns into a gas

All of the above situations

Entropy S is a measure of the amount of disorder in a system ⇒ the greater the disorder the higher the entropy.
The disorder of a system is greatest when a molecule is broken into 2 or more molecules or when a solid turns into a liquid or when a liquid turns into a gas

Law of Thermodynamics Entropy Changes for Reactions