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Changes of state and latent heat

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1. Homework Statement
A 0.2 kg block of ice at -15*C is placed into a pan on a stove, heated to a liquid, and then to vapour with a final temperature of 115*C. Calculate the total amount of heat required for this process.


2. Homework Equations
Eh = mc(t2 - t1)
Lf (or Lv) = Eh / m

3. The Attempt at a Solution
Etotal = Emelting + Evapourization

Emelting = mct
= (0.2kg)(4.2x10^3)(0+15*C)
= 12 600 J

Evapourization = mct
= (0.2kg)(4.2x10^3)(115-0*C)
= 96 600 J

Etotal = 12600 + 96 600J
= 109 200 J or 1.1 x 10^5

What am i doing wrong? The answer is 6.2 x 10^5 J.
 

Answers and Replies

Mapes
Science Advisor
Homework Helper
Gold Member
2,592
17
1) You need to use the correct specific heat capacity for ice, water, and steam.
2) You need to incorporate the latent heat of the phase transformations that occur at 0°C and 100°C.
 

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