Question

Calculate the number of calories released when 20.g of steam condenses at 100.C, cools to 0.C, and freezes. This calculation requires three steps.

Answer 1

To find the energy transfer involved when heating or cooling substances, you need to know the specific heats of the substance. If a state change occurs (solid->liquid, for example), you also need to know the heat of fusion and heat of vaporization.

In this case, you need to know the specific heat of water (how much energy it takes to heat one gram of water by one degree C) as well as the heat of fusion and heat of vaporization (how much energy it takes to melt/boil one gram of ice/water).

Do you have those numbers?

Answer 2

specific heat of water = 1.00cal/gC
heat of fusion for water = 80 cal/g
heat of vaporization for water = 540 cal/g

Answer 3

Now, consider how much water you have- 20 grams. If it takes 80 calories to melt one gram of ice, how many will it take to melt twenty grams?

You can do the same calculation for vaporization.

Answer 4

\[q=(20)(1.00)(100) \times (1/80) \times (540/1)\]

Answer 5

I think i set up the equation right. My answer with sig figs came out to 10,000 calories.

Answer 6

The first half of your equation is good, but you've set the second half up incorrectly.

Condensation, cooling, and freezing are three separate processes that are added together to get the total change in energy. You seem to have multiplied them together.

Can you calculate how much energy is released by condensing the water and how much energy is released by freezing it?