Energy Require from water-steam

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Homework Help Overview

The discussion revolves around calculating the energy required to convert a portion of water at a specific temperature into steam. The problem involves thermodynamic principles, specifically the heat transfer associated with changing the state of water from liquid to gas.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants explore different equations for calculating energy, including the specific heat capacity and latent heat of vaporization. There are attempts to clarify whether to heat all the water to boiling before vaporization or to only consider a portion of it.

Discussion Status

The discussion is active, with participants providing calculations and questioning the steps involved. Some guidance has been offered regarding the correct approach to use latent heat for vaporization, and there is acknowledgment of the need to clarify the mass of water being converted to steam.

Contextual Notes

Participants express uncertainty about the constants used in calculations and the interpretation of the problem statement. There is a mention of personal challenges in recalling high school physics concepts after a significant time away from formal education.

mom2maxncoop
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Homework Statement


How much energy is required to change one quarter of 8.0kg of water at 25°C into steam.




Homework Equations


I get confused to exact what equation to use to figure out the energy required.

I *think* it would be this one:
Q_{t}=M_{water}C_{water}\DeltaT_{water} + .25(M_{water})L_{f}


The Attempt at a Solution


When I do the math, I come up with a ridulous number that makes no sense. I try and try to understand but I can't.

:/.
 
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What are the values of the constants are you using? What value are you getting?
 
Would it be:

Q=mc\Deltat
Q=(8.0kg)(4200J/(kg·°C))(100°C-25°C)
Q=2 520 000

Then since your finding a a quater of it would you then muliply by .25

2520000x.25

=630000J

It seems to easy since the question is worth 5 marks, it feels like I'm missing a step or something :/
 
It boils down to (pun!) whether you are expected to raise all 8.0 kg of water to 100° and then transform 1/4 of it to steam, or whether you are to take 1/4 of 8.0 kg of water and raise its temperature to 100° and then transform it to steam.

Your value for Q looks okay for raising the 8.0 kg of water to 100°. How much additional energy will it take to convert 1/4 of that water at 100° to steam at 100°?
 
I loved the pun, I actually had a giggle with that one!

Right now I'll have to find the mass of the steam itself!
Q=

To find the additional energy would I use the equation that I initially posted (would I use latent fusion or Latent vaporiztion)?

BUT I don't know the mass of the steam nor do I know the Energy, so I have NO Idea where to go next :(:(

(it sucks trying to teach yourself everything from Grade 11 math when you've been out of high school for 6 years :/)
 
The mass is just 1/4 of 8.0 kg. You want to vaporize this mass of water, so you'd use the latent heat of ______?
 
Vaporization since you want to vaporize the mass.

So with that being said

Q=(8.0kg)(4200J(kg·°C)(100°C-25°C)+.25(8.0kg)(2300000)
Q=2520000 + 4600000
Q=7120000J
 
Looks good!
 
Thank you so much!
 

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