Thermodynamics and Entropy Quiz

Grade 12 · Science · Quiz

Test your understanding of thermodynamic laws, entropy, and energy spontaneity.

Questions

The Gibbs free energy equation is:
1. ΔG = ΔH + TΔS
2. ΔG = ΔH − TΔS
3. ΔG = TΔS − ΔH
4. ΔG = ΔU + PΔV
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Answer: ΔG = ΔH − TΔS
The Gibbs free energy equation combines enthalpy and entropy to predict spontaneity: ΔG = ΔH − TΔS. Negative ΔG means spontaneous.
Entropy tends to increase when a solid dissolves into a liquid.
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Answer: True
Dissolution increases entropy because the ordered crystalline structure breaks apart into dispersed ions or molecules.
The ___ Law of Thermodynamics defines thermal equilibrium between systems.
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Answer: Zeroth
The Zeroth Law establishes that thermal equilibrium is transitive — foundational for temperature measurement.
Which process is an example of increasing entropy?
1. Freezing water
2. Crystallization of sugar
3. Evaporation of alcohol
4. Compressing a gas
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Answer: Evaporation of alcohol
Evaporation converts liquid (more ordered) to gas (less ordered), greatly increasing entropy.
A Carnot engine achieves 100% efficiency in theory.
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Answer: False
A Carnot engine achieves maximum possible efficiency for given temperatures: η = 1 − Tc/Th, which is always less than 100% unless Tc = 0 K.
At what temperature does the spontaneity of a reaction with ΔH < 0 and ΔS < 0 change?
1. Never changes
2. At T = ΔH/ΔS
3. At T = 0 K
4. At T = 273 K
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Answer: At T = ΔH/ΔS
When ΔG = 0: ΔH = TΔS, so T = ΔH/ΔS. Below this temperature the reaction is spontaneous; above it the reaction becomes non-spontaneous.
An exothermic reaction releases ___ to the surroundings.
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Answer: heat
Exothermic reactions have negative ΔH, meaning they release heat energy to the surroundings.
The internal energy of an ideal gas depends only on temperature.
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Answer: True
For an ideal gas, intermolecular forces are zero so internal energy depends only on kinetic energy, which depends only on temperature.
Which statement best describes the Second Law of Thermodynamics?
1. Energy is conserved
2. Entropy of the universe increases
3. Entropy at absolute zero is zero
4. Thermal equilibrium is transitive
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Answer: Entropy of the universe increases
The Second Law defines the direction of natural processes — entropy (disorder) of the universe always increases in spontaneous processes.
Heat flowing spontaneously from cold to hot would violate which law?
1. Zeroth Law
2. First Law
3. Second Law
4. Third Law
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Answer: Second Law
The Second Law prohibits spontaneous heat flow from cold to hot without work input, which is why refrigerators require electricity.

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