Unit 7 Review
1.
Compare and contrast solids, liquids, and gases.
2. Convert
a. -16 °C to K
-16 + 273.15 = 257 K
b. 380 K to °C
380 – 273.15 = 107 °C
3. For each of the changes of state listed, state what phase it starts at and what
state it is going to.
a. Freezing __liquid to solid_____________
b. Melting ___solid to liquid_____________
c. Boiling ____liquid to gas_____________
d. Condensation __gas to liquid___________
e. Sublimation ___solid to gas___________
f. Deposition ____gas to solid___________
4. Which changes of state listed above are exothermic processes (i.e. lose kinetic
energy as heat to the surroundings)?
Condensation, freezing, and deposition
5. Which changes of state are endothermic processes?
Melting, Boiling, and Sublimation
6. For each of the following q values, determine if the sign is negative or positive and
if the change is endothermic or exothermic.
a. The system absorbs heat ______+q_____________________
b. Heat is released from the system ____-q_________________
Solve each equation below:
7.
8.
A student finds a rock on the way to school. In the laboratory he
determines that the volume of the rock is 22.7 cm3, and the mass is
39.943 g. What is the density of the rock?
D = ? m = 39.943 g
V = 22.7 cm3
D = 39.943 g
22.7 cm3
D = 1.76 g/cm3
What is the mass of a 350 cm3 sample of pure silicon with a density of
2.336 g/cm3?
D = 2.336 g/cm3
2.336 g/cm3 =
9.
m=?
m
350 cm3
V = 350 cm3
m = 818 g
Pure gold has a density of 19.32 g/cm3. How large would a piece of gold be
if it had a mass of 318.97 g?
D = 19.32 g/ cm3
m = 318.97 g
19.32 g/ cm3 = 318.97 g
V
V=?
V = 16.5 cm3
10. A cubic sample of quartz has a density of 2.65 g/cm3 and the length of one
side of the cube is 4 cm. What is the mass of the quartz sample?
D = 2.65 g/cm3
2.65 g/ cm3 =
V = 4 cm x 4 cm x 4 cm = 64 cm3
m=?
m = 1.70 x 102 g
m
64 cm3
11. A student was asked to determine the density of a spherical object, but she
couldn’t remember the formula for finding the volume of a sphere. She
placed the sphere into a graduated cylinder containing 3.0 ml of water. The
water level rose to 4.5 ml. Then she found the mass of the sphere to be
4.7 g. Calculate the density.
D=m/v
D = ? m = 4.7 g
V = 4.5 mL – 3.0 mL = 1.5 mL
D = 4.7 g
1.5 mL
D = 3.13 g/mL
12. A 120g sample of an unknown substance was heated from 15oC to 30oC. The
substance absorbed 458 joules of energy. What is the specific heat of this
substance?
q = mc(Tf-Ti)
q= 458 J
m= 120 g
c= ?
458 J = 120 g (c) (30 °C – 15 °C)
c = 0.254 J/g°C
Tf= 30 °C
Ti= 15 °C
13. If the temperature of 28 g of ethanol increases from 15oC to 65.5oC, how much
heat was absorbed by the ethanol? (Specific heat ethanol = 2.44 J/goC)
q = mc(Tf-Ti)
q= ?
m= 28 g
c= 2.44 J/g°C
Tf= 65.5 °C Ti= 15 °C
q = 28 g (2.44 J/g°C) (65.5 °C – 15 °C)
q = 3450 J
14. How many grams of water would require 2.20 x 104 joules of heat to raise its
temperature from 34.0°C to 100.0°C? The specific heat of water is 4.184 J/g∙°C
q = mc(Tf-Ti)
q= 2.20 x 104 J
m= ?
c= 4.184 J/g°C
Tf= 100.0 °C
Ti= 34.0 °C
2.20 x 104 J = m (4.184 J/g°C) (100.0 °C – 34.0 °C)
m = 79.7 g
15. A cube of gold weighing 192.4g is heated from 30.0°C to some higher temperature,
with the absorption of 226 joules of heat. The specific heat of gold is 0.030
J/g∙°C. What was the final temperature of the gold?
q = mc(Tf-Ti)
q= 226 J
m= 192.4 g c= 0.030 J/g°C
226 J = 192.4 g (0.030 J/g°C) (Tf – 30.0 °C)
Tf = 69.2 °C
Tf= ? Ti= 30.0 °C
16. A lump of chromium (Cr) has a mass of 92.5 grams and a temperature of 89.5oC. It
is placed into a calorimeter with 75.2 g of water at 20.5oC. After stirring, the final
temperature of the water, Cr metal, and calorimeter is 27.4oC. What is the
specific heat of Cr metal?
q = mc(Tf-Ti)
For Water
q= ?
m= 75.2 g c= 4.184 J/g°C
Tf= 27.4 °C Ti= 20.5 °C
q = 75.2 g (4.184 J/g°C) (27.4 °C – 20.5 °C)
q = 2,170.99392 J
For Metal
q= - 2,170.99392 J
m= 92.5 g c= ?
Tf= 27.4 °C
Ti= 89.5 °C
- 2,170.99392 J = 92.5 g (c) (27.4 °C – 89.5 °C)
c = 0.378 J/g°C
17. A 324 g sample of a metal with a specific heat of 0.82 J/g°C is heated to 100.0°C
then placed in a 50.0 g sample of water at 20.0°C. What is the final temperature of
the metal and the water?
mc(Tf-Ti) = mc(Tf-Ti)
For Water
m= 50.0 g
c= 4.184 J/g°C
T f= ?
Ti= 20.0 °C
For Metal
m= 324 g
c= 0.82 J/g°C
T f= ?
Ti= 100.0 °C
50.0 g (4.184 J/g°C) (Tf – 20.0 °C) = -[324 g (0.82 J/g°C) (Tf – 100.0 °C)]
Tf = 64.8 °C
18. Explain why (in terms of molecular kinetic energy) the heat of vaporization is seven
times larger than the heat of fusion for water.
The heat of vaporization must provide enough energy to break the bonds or IMF’s
between particles, but the heat of fusion only needs to provide enough energy to
loosen them.
19. A liquid will begin to boil when __vapor pressure______ = _atmospeheric pressure.
20. What is the specific condition of pressure for the normal values of freezing or
boiling for a liquid?
1 atm
21. a) What is the critical point for a liquid? And b) what is the triple point for a
substance?
a. A point that marks the highest temperature and pressure combination that a
liquid and gas are distinguishable. The area beyond is a supercritical fluid.
b. A point that marks the temperature and pressure where all three phases will
occur at the same time.
22. Draw a cooling curve for water starting at 110°C going to -10°C (y-axis is °C and xaxis is time)
23. Identify the letters on the phase diagram shown below and place your response in
the spaces provided.
A: _____solid___________________
B:_____liquid___________________
C: _____gas_____________________
D: ____critical point_______________
E: (arrow)___deposition____________