A student burns 0.50 g of ethanol (M = 46.0 g/mol) which releases 1360 kJ per mole. The energy heats 200 g of water, but only 60 percent of the energy reaches the water (c = 4.18 J/g/K). The temperature rise is closest to:

Answer and explanation

Correct answer: C. 10.6 degrees Celsius

  1. Step 1: n(ethanol) = 0.50 / 46.0 = 0.01087 mol.
  2. Step 2: Energy released = 0.01087 x 1360 = 14.78 kJ; 60 percent reaches the water: 8.87 kJ = 8870 J.
  3. Step 3: Temperature rise = 8870 / (200 x 4.18) = 10.6 degrees Celsius.
Answer
10.6 degrees Celsius.
Why not the others: 17.7 degrees Celsius assumes 100 percent transfer; 6.4 applies the 60 percent twice; 5.3 uses 400 g of water.

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