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Chemistry I-Honors

Change-of-State Problems – Solution Set

Terms to remember:

o

o

o

C for H

O

= 4.184 joule/g

C; C for H

O

= 1.84 joule/g

C;

C for H

O

= 2.09 joule/g

C

2

(liq)

2

(gas)

2

(solid)

For K.E.:

Heat = m x C x t

For P.E.:

Heat = m x H

[ H

= 2260 joule/g];

Heat = m x H

[ H

= 334 joule/g]

V

V

F

F

o

o

1. How many kilojoules are needed to convert 80.0 grams of cold water at 0

C to hot water at 95.0

C?

o

o

31.8 kJ

Q = mC t = [(80.0 g)(4.184 J/g-

C)(95.0

C)]/1000 =

o

o

2. How many kilojoules are needed to convert 14.4 grams of ice at -80.0

C to water at 61

C?

o

o

2.41 kJ

Q

= mC t = [(14.4 g)(2.09 J/g-

C)(80.0

C)]/1000 =

1

4.81 kJ

Q

= m H

= [(14.4 g)(334 J/g)]/1000

=

2

fusion

o

o

kJ

3.67

Q

= mC t = [(14.4 g)(4.184 J/g-

C)(61.0

C)]/1000 =

3

10.9 kJ

Q

=

total

o

3. If 6.50 KJ are used to heat 63.0 grams of water at 20.0

C, what will be its final temperature?

o

o

21.09 kJ (too much!)

Q

= mC t = [(63.0 g)(4.184 J/g-

C)(80.0

C)]/1000 =

1

o

o

Then 6500 joules = (63.0 g)(4.184 J/g-

C)(X – 20.0

C)

o

X = final temperature = 44.7

C

o

o

4. How many kilojoules are required to convert 325 grams of ice at 0

C to steam at 176

C?

109 kJ

Q

= m H

= [(325 g)(334 J/g)]/1000

=

1

fusion

o

o

kJ

136

Q

= mC t = [(325g)(4.184 J/g-

C)(100.0

C)]/1000 =

2

735 kJ

Q

= m H

= [(325g)(2260 J/g)]/1000

=

3

vapor

o

o

45 kJ

Q

= mC t = [(325g)(1.84 J/g-

C)(76

C)]/1000

=

4

1020 kJ

Q

=

total

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Parent category: Education