June 2010 Chemistry Regents #59-61

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Base your answers to questions 59 through 61 on the information below.

Heat is added to a 200.-gram sample of H2O(s) to melt the sample at 0C. Then the resulting H2O() is heated to a final temperature of 65C.

59 Determine the total amount of heat required to completely melt the sample. [1]

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ANSWER= 66 800 J   or   6.68 104 J

NOTE=the question was only asking for the energy to melt

Q=mHf

Q=200g(334J/g)

60 In the space in your answer booklet, show a numerical setup for calculating the total amount of heat required to raise the temperature of the H2O() from 0C to its final temperature. [1]

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Just the setup (DON'T ANSWER IT)

Q=mCDT

q = (200. g)(4.18 J/gC)(65C)

(200)(4.18)(65)

61 Compare the amount of heat required to vaporize a 200.-gram sample of H2O() at its boiling point to the amount of heat required to melt a 200.-gram sample of H2O(s) at its melting point. [1]

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NOTE=Hv (2260J/g) vs. Hf (334J/g)

The heat necessary to vaporize 200 grams of water is about seven times larger than the heat necessary to melt 200 grams of ice.

It takes more heat to vaporize the same amount of H2O().

 

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