Quiz | Chemical Thermodynamics
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
What is the expression of the Gibbs energy change?
ΔGrxn = ΔHrxn + TΔSrxn
ΔGrxn = ΔHrxn - TΔSrxn
ΔGrxn = ΔHrxn - RTΔSrxn
ΔGrxn = ΔHrxn/T + ΔSrxn
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
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
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
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 = - + ⇒ a plot of ln K versus is linear (ln K and are proportional)
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