# How long does it take to boil away 0.4L water from a copper pot?

Sam
This one has me stumped. Please help me solve.

Thank you!

Time

A copper pot is heated by a burner which is at 195 ° C. If the water in the pot is boiling, how long does it take in seconds to boil away 0.4 L? The diameter of the pot is 27 cm, and it is 3.5 mm thick.

k copper = 9.4 · 10^-2 kcal/(m · s ° C)

## Answers and Replies

gnome
It's not too difficult if you can ignore any heat conducted up through the sides of the pot.

You have to determine the amount of heat needed to vaporize .4L of water, and divide by the rate at which heat is conducted through the copper base (assuming that the burner always supplies enough heat energy to maintain the outside temperature at the bottom of the pot at 195 degrees.

Can you do that?

I get 1.48 seconds. (Hope I haven't messed up the arithmetic.)

On the other hand, if conduction through the sides of the pot must be included, I don't think it can be done without knowing the depth of the water in the pot (but in that case I wouldn't know how to do it anyway )

Sam
Thanks

I did get 1.478607576 seconds, rounded to 1.48. I just forgot to take the thickness of the pot into consideration.

Thanks for the help.

arcnets
Sam,
I arrived at the same answer, but this looks very suspicious to me: Boil away .4L of water in 1.4 secs in such a small pot? I call that an explosion.
Imagine you have your pot at 195°C, and pour in the water (let's say there's a bulk of hot material underneath so the water can't cool down the pot). What will probably happen is a big mess, after which you'll have to clean up the lab (if you're still alive ).

If I was you, I'd ask my prof what's the good of a problem like this.