How many grams of water at 20 degrees Celsius can be converted into steam

[DB]

can someone give me a hand on this one?

How many grams of water at 20 degrees Celsius can be converted into steam at 500 degrees Celsius with 10 kJ of energy?

wat i know is that this question is 2 parts: Water being heated to 100 C (80 C change)using the specific heat of water n then having a temperature change of 400 C using the specific heat of steam.

wat i don't understand is how i am supposed to split up the 10 kJ? do i have to have only 1 equation?

thanks in advance

 

[DB]

sorry guys, i just realized there was a chemistry section, my bad...

 

[Doc Al]

There are three steps: (1) Heating the water, (2) converting water to steam, (3) Heating the steam.

Express the heat required for each step in terms of the mass, m. Set the total energy equal to 10 kJ. That's the equation you want.

 

[DB]

okay but should i have 3 equations or 1?

 

[Doc Al]

You'll end up with a single equation. (Reread my previous post.)

 

[DB]

i don't no wat u mean when u say express the heat in terms of mass

 

[DB]

wat i tried was adding each step and then dividing 10000J by the sum to solve for m, i got 2.94 grams...?

 

[Doc Al]

i don't no wat u mean when u say express the heat in terms of mass

For example: For step 1, how much heat is required to heat "m" grams of water from 20 degrees to 100 degrees?

 

[DB]

okay so now I've got 3 values for "m":

$$m=\frac{E}{80*4.19}$$

$$m=\frac{E}{2262}$$

$$m=\frac{E}{400*2.01}$$

now I am stuck :(

 

[Doc Al]

There is only one "m". What you should have is three values for E: $$E_1, E_2, E_3$$. Your equation would be: $$E_1 + E_2 + E_3$$ = 10 kJ; solve for m.

 

[DB]

ya that's wat i did when i said i got 2.94 grams

 

[DB]

anyway I am convinced that the answer is 2.94 grams, thanks for the tips doc al, i apreciate it