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Topic: How much heat energy required to convert following? Check my answer  (Read 31648 times)

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Offline benworld128

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How much heat energy required to convert following?

How much heat energy, in kilojoules, is required to convert 47.0 g of ice at -18.0 C to water at 25.0 C ?

Specific Heat of Ice - 2.09 j/g * c

This is how I did it and the answer is wrong...Please check and correct me

Q = m * Cice * Change in Temp

Q = (47.0 g)(2.09 J/g*c)(43) = 4222.6 J * 0.001 kj / j = 4.22 kj

Offline DrCMS

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Re: How much heat energy required to convert following? Check my answer
« Reply #1 on: September 11, 2011, 10:44:58 AM »
This is a 3 part question and you have done the 2nd part wrong but not done the 1st or last parts at all, that is why your answer is wrong.

You need to calculate
1) the energy needed to raise the ice from -18C to 0C  (this uses the specific heat capacity of ice)
2) the energy required to melt that ice ( this uses the latent heat of fusion for water)
3) the energy required to raise the temp of the water from 0C to 25C  (this uses the specific heat capacity of water)

Offline benworld128

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Re: How much heat energy required to convert following? Check my answer
« Reply #2 on: September 11, 2011, 12:35:35 PM »
Given Following:

    Specific heat of ice: =2.09
    Specific heat of liquid water:4.18
    Enthalpy of fusion: 334
    Enthalpy of vaporization: 2250



1. Energy for 18 to 0 * C

Q = M * Cs * T

(47)(2.09)(18) = 1.76 kj

2. Fusion Energy

Q = M * Change in Fusion      Enthalpy of Fusion Given = 334 J

(47)(334 j) = 15.03 KJ

3. Energy for 0 to 25 * C

(47)(4.18)(25) = 4.91 kj

4. Add all of it up

1.76 + 15.03 + 4.91 = 21.7 kj

Is the answer 21.7 KJ correct

Offline benworld128

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Re: How much heat energy required to convert following? Check my answer
« Reply #3 on: September 11, 2011, 01:28:52 PM »
anyone

Offline DrCMS

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Re: How much heat energy required to convert following? Check my answer
« Reply #4 on: September 11, 2011, 04:00:40 PM »
You have the correct approach now but the wrong answer.

You have rounded the 1st answer incorrectly

The 2nd part is wrong because you've used 45 instead of 47g.

Also only round the final answer not each part answer.

Offline benworld128

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Re: How much heat energy required to convert following? Check my answer
« Reply #5 on: September 11, 2011, 10:08:48 PM »
The first answer is correct no ?

1. Energy for 18 to 0 * C

Q = M * Cs * T

(47)(2.09)(18) = 1768.14 J * 0.001 Kj = 1.76 KJ ?

2.  I used 47g not 45 ?

So I redid all calculation and this time I got 22.4 kj   is that right ?

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