# The Naked Scientists Forum

### Author Topic: a question of help  (Read 2411 times)

#### martin baker

• First timers
• Posts: 3
##### a question of help
« on: 15/02/2006 13:51:54 »
hello, I wonder if anyone can answer this question for me?

it contains alot of varibles so maybe impossible to answer...

I require heating a 100ml body of water to 50oc and keeping it at that temp untill all the water has evaporated.

Could anyone tell me how much energy i require. Im aware that the starting temp of the water is important and that the relative humidity and air temp will effect the amount of energy required.

if anyone has an answer of suitable equations i could use i would be most grateful.

cheers

#### daveshorts

• Moderator
• Neilep Level Member
• Posts: 2583
• Physics, Experiments
##### Re: a question of help
« Reply #1 on: 15/02/2006 17:19:44 »
assuming no conductive or convective losses:

water takes 4.2 J/g/C  to warm up so as 1ml weighs pretty much 1g it will take:
(50C-starttemp)*100g*4.2J/g/C   joules to heat it to 50C

to evaporate water it takes 2.26kJ/g  at 100C (but we will guess it is about the same at 50C, to avoid lots of thermodynamics)
this is called the latent heat of vapourisation

so this will take 100g*2.26kJ/g = 226kJ

does that help?
« Last Edit: 15/02/2006 17:21:37 by daveshorts »

#### martin baker

• First timers
• Posts: 3
##### Re: a question of help
« Reply #2 on: 15/02/2006 18:58:07 »
cheers, that helps alot as i now begin working out if a suitable battery exist to do the job or how much butane would be required

#### The Naked Scientists Forum

##### Re: a question of help
« Reply #2 on: 15/02/2006 18:58:07 »