Calculate the energy?

Question

Calculate the energy released when 10.0g of steam at 100oC, 1 atm is condensed and cools to 25oC. PLEASE show workings on how to do this problem.

Answer 1

First off, the 10g steam is already down to 100C, so we don't have to worry about the heat capacity of steam. The only thing that comes next is what is called the latent heat of vaporization of water.That's actually backwards, because we are condensing water vapor. The two are same, however, because of the First Law of Thermodynamics. Anyway, let steam and water be called W.

10.0gW x 512cal/g = 5120 cal

The 512 cal/g comes from the latent heat of vaporization of water. Next, the heat capacity of water is 1cal/deg-g. People often confuse heat capacity with specific heat. Heat capacity has particular units. Specific heat is a ratio. That does not matter now. As you go on in chemistry, it will.

10gW x 75degC x 1cal/g-deg = 75cal

The 75deg comes from the cooling down of the water from 100C to 25C.

5120cal + 75cal = 5195cal

The astounding thing to be learned from this problem is the enormous amount of heat given off by the 10.0g steam in just condensing from steam at 100C to water at the same temperature, 100C. Next, cool the water from boiling to room temperature, and that takes only 75cal.