# Homework Help: How much heat will be lost

1. Jul 28, 2010

### missileblitz

Question #1
1. The problem statement, all variables and given/known data
How much heat will be lost when 120 g of steam at 100°C is condensed to water at 80°C?

2. Relevant equations

Q = mc∆t
Q = m LV

3. The attempt at a solution

Q = mc∆t
Q = 0.12 x 4186 x (80 – 100)
Q = 10046.4 J
Q = m LV
Q = 0.12 x (- 2.3 x 106)
Q = 276000 J
= 10046.4 + 276000 = 286046.4
= -2.9 x 105 J

Is the latent heat of condensation negative to that of vaporization?

Question #2
1. The problem statement, all variables and given/known data
If 20 g of ice at 0° is added to 180 g of water at 22°C, what will the final temperature of the water be?

2. Relevant equations
Q = mc∆t

3. The attempt at a solution
mc∆t = mc∆t
0.02 x 2050 (0-T) = 0.18 x 4186 (T-22)
-41T = 753.48T - 16576.56
-794.48T = -16576.56
-794.48T/-794.48 = -16576.56/-794.48
T = 20.86

For this question, is the latent heat of fusion needed?

Last edited: Jul 28, 2010
2. Jul 28, 2010

### Mapes

Yes, it has the opposite sign, as energy is required for vaporization but released by condensation. You calculations look good.

3. Jul 28, 2010

### missileblitz

Thanks for the reply! I'd like someone to confirm the second question too. Thanks in advance.

4. Jul 28, 2010

### missileblitz

:O no one?

5. Jul 28, 2010

### rl.bhat

Heat lost by water = mwc(22 - t)

Heat gained by the ice = miL + mic(t-0) where L is the latent heat of fusion of ice.

Now solve for t.

6. Jul 29, 2010