**CHM
2045C Module Seven Sample Exam Answers **

**Module
Seven Part D: Enthalpy change with Phase Change/Ice Cube Problem 5 points**

**Phase
Change (3 points):**

1. Calculate the amount of heat necessary to melt **27.0 grams of ice at 0 ^{o}C**, if the

**q _{melting}**

If I had the same amount of water
at 100^{o}C, calculate the amount of heat required to boil **27.0 grams of water** if the **heat of vaporization ΔH _{vap} of water is 2256 J/g**?

**q _{boiling}**

How much heat is required to
raise the temperature of the **27 grams of
water at 0 ^{o}C to 100^{o}C**, if the

**q _{H2O}
= C_{H2O} x m x ΔT **

**q _{H2O}
= (4.184 J/g**

**Ice
Cube Problem (2 points):**

If **27.0 grams of ice at 0 ^{o}C is **added
to an insulated

**q _{melting}**

**From the above
examples**

**(27.0g ice)(333
J/g) + (27.0 g)(4.184 J/g**^{ oC}**)(T – 0)**^{ oC}** +
(123g) (4.184 J/g ^{ oC}
)(T – 50) ^{o}C = 0**

**multiple****
equation by ^{o}C;
divide equation by J to simplify units:**

**8991 ^{o}C
+ 113.0T + 514.6T –
25732 ^{o}C = 0 **

**627.6 T – 16741 ^{ oC} = 0**

**627.6 T = +16741 ^{ oC}**

** T = 26.7 ^{o}C**