Thermodynamics and Energy Quiz

Grade 10 · Science · Quiz

Test your understanding of energy changes, enthalpy, entropy, and Gibbs free energy in chemical and physical processes.

Questions

1. A reaction has ΔH = +100 kJ and ΔS = -200 J/K. At 500 K, what is ΔG and is the reaction spontaneous?

   1. ΔG = -100 kJ, spontaneous
   2. ΔG = +200 kJ, not spontaneous
   3. ΔG = +100 kJ, not spontaneous
   4. ΔG = -200 kJ, spontaneous
   Show answer

   Answer: ΔG = +200 kJ, not spontaneous

   ΔG = ΔH - TΔS = 100,000 J - (500 K)(-200 J/K) = 100,000 + 100,000 = +200,000 J = +200 kJ. Positive ΔG means non-spontaneous

2. Given: C + O₂ → CO₂, ΔH = -393.5 kJ and 2CO + O₂ → 2CO₂, ΔH = -566.0 kJ. Using Hess's Law, what is ΔH for 2C + O₂ → 2CO?

   1. −221.0 kJ
   2. −172.5 kJ
   3. −959.5 kJ
   4. −787.0 kJ
   Show answer

   Answer: −221.0 kJ

   Target: 2C + O₂ → 2CO. Use 2×(C+O₂→CO₂): 2(-393.5)=-787 kJ, then reverse 2CO+O₂→2CO₂: +566.0 kJ. Total: -787 + 566 = -221 kJ

3. Which of the following processes has the greatest increase in entropy?

   1. Dissolving NaCl in water
   2. Freezing liquid water
   3. Sublimation of dry ice (CO₂(s) → CO₂(g))
   4. Combining two solutions of the same liquid
   Show answer

   Answer: Sublimation of dry ice (CO₂(s) → CO₂(g))

   Sublimation converts solid directly to gas, producing the largest increase in disorder/randomness among these options

4. A calorimeter contains 200 g of water at 25°C. A reaction releases 8368 J of heat. What is the final temperature? (c_water = 4.184 J/g·°C)

   1. 15°C
   2. 35°C
   3. 45°C
   4. 50°C
   Show answer

   Answer: 35°C

   q = mcΔT → ΔT = q/(mc) = 8368/(200 × 4.184) = 8368/836.8 = 10°C. Final T = 25 + 10 = 35°C

5. What does a negative value of ΔG indicate about a chemical reaction?

   1. The reaction requires heat input
   2. The reaction is spontaneous under the given conditions
   3. The reaction cannot occur at any temperature
   4. The reaction absorbs energy from the surroundings
   Show answer

   Answer: The reaction is spontaneous under the given conditions

   ΔG < 0 means Gibbs free energy decreases — the reaction releases usable energy and proceeds spontaneously

6. The specific heat of aluminum is 0.900 J/(g·°C). How much heat is released when 100 g of aluminum cools from 200°C to 25°C?

   1. 900 J
   2. 2250 J
   3. 15750 J
   4. 22500 J
   Show answer

   Answer: 15750 J

   q = mcΔT = 100 g × 0.900 J/(g·°C) × (200-25)°C = 100 × 0.900 × 175 = 15,750 J released

7. A reaction with ΔH > 0 and ΔS < 0 can be spontaneous at high temperatures.

   Show answer

   Answer: False

   ΔG = ΔH - TΔS. When ΔH > 0 and ΔS < 0, ΔG is always positive regardless of temperature — never spontaneous

8. The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states is called the standard enthalpy of ________.

   Show answer

   Answer: formation

   Standard enthalpy of formation (ΔHf°) is the enthalpy change for forming 1 mole of compound from elements in standard states at 25°C and 1 atm

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