Someone help with physics please?

Question

Can someone please help me out with a physics question. I solved my other question but I'm just having trouble with this one. If you guys can help me out, it would be so appreciated:
A 500 watt electric heater is used to boil 2kg of water at 40 degrees celcius into steam at 130 degrees celcius. <---assume constant volume.
a) Determine the amount of thermal energy required.
b) If the process takes 3.5 hours determine the efficiency of the heater.
I know you guys will need specific heat capacities and latent heat vapourization and all those so please email me at [e-mail] and I'll respond right back. If you you don't want to type then you can write it and then scan it. I hope I don't sound demanding, but just any help would be really good right now as I'm struggling. I can't ask my teacher as it's an assignment nor any of my classmates; they all have different assignments. It would be better if you guys could help me in emails instead of here.But any help u offer then thank U

Answer 1

I think you can do it easily.

Answer 2

for a) just remember that specific heat is the amount of heat required to have a 1 degree change in temperature per kilogram, so

q = (mass)*(temperature rise)*(specific heat) -----> answer should be in Joules

for b) a 500 watt heater emits 500*60*60*3.5 = 6300000 Joules of heat in 3.5 hours. Compare that with the answer from (a) to find the efficiency.




EDIT: I just realized that the water actually goes above it's boiling point (assuming atmospheric pressure). Although, you said "assume constant volume", so I guess that means it doesn't boil. If it does boil, you have to add extra energy (vaporization) to the equation for part (a).

Answer 3

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