# Homework Help: Heat Capacity

1. Oct 8, 2009

### DarkPhoenix

https://www.physicsforums.com/attachment.php?attachmentid=21003&stc=1&d=1255013927

I need help for number 2(b)

A student investigates the evaporation of water. He pours 100 cm3 of water into measuring
cylinder A and 100 cm3 of water into measuring cylinder B. Measuring cylinder A is kept
at 40 °C and B is kept at 80 °C in the same part of the laboratory. Fig. 2.1 shows the two
measuring cylinders after 3 days.

The specific latent heat of vaporisation of water is 2300 J / g and the density of water is
1.0 g / cm3. During the three days, the water level in B drops from the 100 cm3 mark to
the level shown in Fig. 2.1. Calculate the energy used to evaporate water from B during
the three days.

Volume = (80-60) = 20 cm3

1 cm3 = 1 g
20 cm3 = 20 g

Q= ml
Q= 20/1000 x 2300

Thanks.

2. Oct 8, 2009

### Delphi51

I see 2 difficulties.
First, the 20 grams should not be converted to kg because the latent heat "2300 J / g" is in grams, not kg.

Second, I think you have to add the heat required to warm the 20 g up to 100 degrees.