Chem Unit 3 Practice Exam PDF
Chem Unit 3 Practice Exam PDF
Chem Unit 3 Practice Exam PDF
____ 1. Two gases with unequal masses are injected into opposite ends of a long tube at the same time and allowed to
diffuse toward the center. They should begin to mix
a. in approximately five minutes.
b. closer to the end that holds the heavier gas.
c. closer to the end that holds the lighter gas.
d. exactly in the middle.
____ 4. According to the kinetic-molecular theory, which substances are made of particles?
a. gases only c. all matter
b. liquids only d. all matter except solids
____ 10. By which process do gases take the shape of their container?
a. evaporation c. adhesion
b. expansion d. diffusion
Page 2 – Unit 3 Practice Exam
____ 11. According to the kinetic-molecular theory, how does a gas expand?
a. Its particles become larger.
b. Collisions between particles become elastic.
c. Its temperature rises.
d. Its particles move greater distances.
____ 14. Which term best describes the process by which particles escape from the surface of a nonboiling liquid and
enter the gas state?
a. sublimation c. surface tension
b. evaporation d. aeration
____ 15. A solid forms when the average energy of a substance's particles
a. increases. c. decreases then increases.
b. decreases. d. creates a random arrangement.
____ 19. If the rate of evaporation from the surface of a liquid exceeds the rate of condensation,
a. the system is in equilibrium.
b. the liquid is boiling.
c. energy as heat is no longer available.
d. the concentration of the vapor is increasing.
____ 20. When energy as heat is applied to a liquid-vapor system at equilibrium, a new equilibrium state will have
a. a higher percentage of liquid. c. equal amounts of liquid and vapor.
b. a higher percentage of vapor. d. all liquid.
Use the phase diagram for water to answer the questions 23 thorugh 27.
24. What state exists above the curve AB and to the left of the curve AD?
29. Water has a heat of vaporization of ± 2266 J/g. How many grams of water can be condensed by releasing
2023 J of energy?
30. How much energy is required or released to cool 28.3 g of steam (water vapor) at 100.0°C to liquid water at
25.5°C? Water has a heat of vaporization of ± 2266 J/g and a specific heat of 4.184 J/g°C.
SHORT ANSWER
23. ANS:
C is the critical point.
24. ANS:
The solid phase.
25. ANS:
A is the triple point.
26. ANS:
The gas state.
27. ANS:
The liquid state.
NUMERIC RESPONSE
30. ANS:
Phase Change Q = (28.3 g) x (-2266 J/g) = - 64128 J (3 s.f.)
Temp Change Q = (28.3 g) x (4.184 J/g°C) x (25.5°C - 100.0°C) = - 8821 J (3 s.f.)
Total Energy = - 64126 J + (- 8821 J) = - 72900 J (s.f. to the hundreds digit)
ESSAY
31. ANS: The particles in both gas and liquid states have random motion and the particles can move past each
other. Gas particles have a higher temperature than liquid particles and therefore more thermal energy and a
faster speed of motion than liquid particles. Gas particles have more interaction energy than liquid particles
and therefore a greater rand of motion than liquid particles.