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PCAT Chemical Processes – Molar Heat Capacities

The molar heat capacities (J/mole ŸK) for zinc, copper, silver, and gold is 25.2, 24.5, 24.9, and 25.6, respectively. If 1 mole of each substance is heated until the temperature increases by 10K, which metal required the addition of the most heat?

  1. Zinc
  2. Copper
  3. Silver
  4. Gold
Click for Explanation

This question asks you to apply information on molar heat capacities to determine the most energetically intensive material. Since the change in temperature and the quantity of each substance is constant, the difference in molar heat capacities dictates the energy requirements for each substance.

Molar heat capacity tells you how much energy (J) is necessary to increase one mole of a substance by 1 K. Therefore, the higher the molar heat capacity, the more energy required. In the question above, gold has the highest molar heat capacity and therefore requires the greatest amount of heat. The calculations are given below.

Energy = (molar heat capacity) x (# of moles) x (change in temperature)

Zinc: (25.2 J/mole ŸK) x (1 mole) x (10 K) = 252 J
Copper: (24.5 J/mole ŸK) x (1 mole) x (10 K) = 245 J
Silver: (24.9 J/mole ŸK) x (1 mole) x (10 K) = 249 J
Gold: (25.6 J/mole ŸK) x (1 mole) x (10 K) = 256 J

Multiplying the molar heat capacity by the number of moles and the change in temperature gives you energy required. Gold requires the most heat (256 J) making answer choice D correct.

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