Asked by Riana

How much heat would it take to change 1.0kg of water at 20°C to steam at 110°C.

I can't get the right answer that is 2.6×10^6J. Please tell me how can I solve this problem, I want to learn how to solve These problem plz help me.
Answered by bobpursley
you have three parts:
a. Heat the water to 100C
b. vaporize the water at 100C
c. heat the steam to 110C

a. heat=m*cwater*(100-20)
b. heat=m*Hv
c. heat=m*csteam*(110-100)
cwater is specific heat capacity of water
Hv is the heat of vaporization of water.
Csteam is specific heat capacity of steam (it is not the same as water)
Answered by Riana
For (a)336000J
(B) 2255j
(C) 20000j

I added them and the answer is 358255j
Which is totally different from the correct answer ....am I doing it right ?
Answered by bobpursley
No.

You have to use units here. What units of mass, specific heat did you use? Notice the units in the table for specific heat, and heat vaporization. That is where You erred.
Answered by Riana
OK I converted °C to K but the answer now is 4304530J
Answered by Riana
Did you solved the problem? Is it 2.6×10^6J?
I don't know where I am doing it wrong...I checked my work thrice but still the answer is wrong.
Answered by bobpursley
You did not convert celcius to kelvins. They have the same unit.

I will do
a) for you
heat=1kg*cw*(80C)
in my table, cw is is in J/gram*C

heat=1000g*4.186J/gC*80C== 334880J
b) heat=mass*Hv
my table has Hv as 2260 J /g, again mass units is grams
Heat=1000*2260=2,260,000 J
See my point? you have to include units, Then, when you get the three answers, THEY HAVE to be in the same units to add. Yours was NOT.
Answered by Riana
But my table have specific heat in J/kg.k
And latent heat in kJ/kg
That's why I only converted °c to k and
kJ into J
Answered by Riana
Can you please tell me what value of specific heat did you used for q3?
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