Thermodynamics Quiz

Grade 11 · Science · Quiz

10 questions on energy transfer, enthalpy, entropy, spontaneity, and the laws of thermodynamics.

Questions

1. Which law states that energy cannot be created or destroyed?

   1. Zeroth Law
   2. First Law
   3. Second Law
   4. Third Law
   Show answer

   Answer: First Law

   The First Law of Thermodynamics is the law of energy conservation.

2. A reaction has ΔH = +30 kJ and ΔS = −50 J/K. Which is correct?

   1. Spontaneous at all temperatures
   2. Spontaneous only at high T
   3. Spontaneous only at low T
   4. Nonspontaneous at all temperatures
   Show answer

   Answer: Nonspontaneous at all temperatures

   ΔH > 0 and ΔS < 0 means ΔG is always positive — never spontaneous.

3. Which reaction has the largest predicted increase in entropy?

   1. 2H₂O(l) → 2H₂(g) + O₂(g)
   2. N₂(g) + 3H₂(g) → 2NH₃(g)
   3. NaCl(s) → NaCl(l)
   4. CO₂(g) → CO₂(s)
   Show answer

   Answer: 2H₂O(l) → 2H₂(g) + O₂(g)

   Converts liquid to gas and increases gas moles from 0 to 3 — both strongly increase entropy.

4. Using Hess's Law: Reaction 1 ΔH = −100 kJ, Reaction 2 ΔH = +40 kJ. Overall ΔH?

   1. +140 kJ
   2. −60 kJ
   3. +60 kJ
   4. −140 kJ
   Show answer

   Answer: −60 kJ

   Hess's Law: sum the ΔH values. −100 + 40 = −60 kJ.

5. What is the sign of ΔG for a spontaneous process?

   1. ΔG > 0
   2. ΔG = 0
   3. ΔG < 0
   4. Any value
   Show answer

   Answer: ΔG < 0

   Negative ΔG means the process releases free energy and occurs spontaneously.

6. The Third Law establishes that entropy equals zero when:

   1. A gas is at maximum compression
   2. A perfect crystal is at 0 K
   3. A system reaches equilibrium
   4. All molecules stop at 273 K
   Show answer

   Answer: A perfect crystal is at 0 K

   A perfect crystal at 0 K has only one microstate (no disorder), so S = 0.

7. In ΔG = ΔH − TΔS, what does T represent?

   1. Temperature in Celsius
   2. Temperature in Kelvin
   3. Time in seconds
   4. Thermal conductivity
   Show answer

   Answer: Temperature in Kelvin

   T must be in Kelvin to ensure consistent units in the Gibbs equation.

8. An exothermic reaction releases 250 kJ of heat. What is ΔH?

   1. +250 kJ
   2. −250 kJ
   3. 0 kJ
   4. +125 kJ
   Show answer

   Answer: −250 kJ

   Exothermic reactions have negative ΔH — the system loses heat to surroundings.

9. Which correctly describes the Second Law?

   1. Energy is conserved in all processes
   2. Entropy of the universe always increases in spontaneous processes
   3. A perfect crystal has zero entropy at 0 K
   4. Heat flows from cold to hot spontaneously
   Show answer

   Answer: Entropy of the universe always increases in spontaneous processes

   ΔS_universe > 0 for any spontaneous process — the Second Law.

10. Calculate ΔG at 500 K if ΔH = −20 kJ and ΔS = +60 J/K.

    1. −50 kJ
    2. −80 kJ
    3. +50 kJ
    4. +10 kJ
    Show answer

    Answer: −50 kJ

    ΔG = −20,000 J − (500)(60) = −20,000 − 30,000 = −50,000 J = −50 kJ.

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