# Homework Help: Latent Heat Question

1. Apr 23, 2014

### Bgerst103

1. The problem statement, all variables and given/known data

A scientist heats up a substance by applying heat at a constant rate of 75 J/s. She measures that
it takes 1 minute for 100 grams of the substance to evaporate. What is the latent of vaporization
of this substance? If she starts with 1 kg of the substance, how long will it take for it to
evaporate and how much energy will it take to evaporate the substance?

2. Relevant equations

Q=mL?

3. The attempt at a solution[/b

I'm not really sure how to use Q=mL. Does 75 J/s go into Q or is Q the total amount of joules. I know m is the mass and L is the specific latent heat.

2. Apr 23, 2014

I will use the formula $E=mL_v$ for easiness.
J/s is the unit of power so if you know the power and the time,you should be able to find the energy supplied.
Use$E=mL_v$ to find the $L_v$.

3. Apr 23, 2014

### Bgerst103

So, 75 x 60 is equal 4500. 4500= (.1kg)(L) -> L=45000. If it takes 1 minute to vaporize 100g it should take 10 minutes for a kg and 45000 J?

4. Apr 23, 2014