Heat Problem Help

Question

A) How many calories of heat are released when 500 grams of steam at 120°C are converted to ice at -4.0°C?

B) A swimming pool is 4.0 meters wide and 10 meters long and has a depth of 1.5 meters. it is filled to the top with water at 16°C. How much heat must be added to bring the temperature of the water to 32°C?

Answer 1

Hey Ivan,

A) Heat problems involving a change of phase typically have a bunch of steps, as this one does:

1. Use the specific heat of steam to calculate how much energy is released when this 500-gram sample changes 20 degrees (from 120 to 100).
2. Use the heat of vaporization to calculate how much heat is released when this steam changes into water.
3. Use the specific heat of water to calculate how much energy is released when this 500-gram sample changes 100 degrees (from 100 to 0).
4. Use the heat of fusion to calculate how much heat energy is released when this sample changes into ice
5. Use the specific heat of ice to calculate how much heat energy is released when it changes 4 degrees (from 0 to -4).

Add them all up and you have your final answer. Note that if you follow the math of the formulas perfectly, all of your numbers including your answer will be negative. That's because the heat is being released. But with the way the question is phrased, your answer is positive.

B) This one is easy by comparison.

1. Use the dimensions of the pool to calculate its volume
2. Use the density of water to calculate the mass of that volume of water
3. Use your specific heat formula to calculate the heat needed to raise the temp by 16 degrees. Watch out for units. If your value for specific heat is given in J/deg.C/g, then you'll need the mass of water in grams.

Good luck!