# answer key for gas laws practice worksheet ```Unit 7 Question Packet
Gases
SKILLS
1.
2.
3.
4.
Name …………………KEY………………………
Period ………….
understanding KINETIC MOLECULAR THEORY
calculating PRESSURE, VOLUME, OR TEMPERATURE OF A GAS
applying THE IDEAL GAS LAW
SKILL #1:
understanding KINETIC MOLECULAR THEORY
1. Two basic properties of the gas phase are
(1) a definite shape and a definite volume
(2) a definite shape but no definite volume
2.
- refer to your notes &amp; RB p. 9
(3) no definite shape but a definite volume
(4) no definite shape and no definite volume
Summarize the four parts of the Kinetic Molecular Theory (KMT).
 Gas particles in constant, random, straight-line motion
 Elastic collisions between gas particles (energy is conserved)
 Volume of gas particles is negligible.
 Gas particles are not attracted to each other.
3. According to the kinetic molecular theory, the molecules of an ideal gas
(1) have a strong attraction for each other
(2) have significant volume
(3) move in random, constant, straight-line motion
(4) are closely packed in a regular repeating pattern
4. According to the kinetic molecular theory, which assumption is correct?
(1) Gas particles strongly attract each other.
(2) Gas particles travel in curved paths.
(3) The volume of gas particles prevents random motion.
(4) Energy may be transferred between colliding particles.
5. What are the two reasons why real gases do not behave exactly like ideal gases?
 Real gases have IMF.
 Real gas particles have volume.
6. Real gases behave most like ideal gases under conditions of (circle one)
high / low pressure
and
high / low
temperature
7. Helium is most likely to behave as an ideal gas when it is under
(1) high pressure and high temperature
(2) high pressure and low temperature
(3) low pressure and high temperature
(4) low pressure and low temperature
8. Under which conditions of temperature and pressure does oxygen gas behave least like an ideal
gas?
(1) low temperature and low pressure
(2) low temperature and high pressure
(3) high temperature and low pressure
(4) high temperature and high pressure
9. Under which conditions of temperature and pressure would a real gas behave most like an ideal
gas?
(1) 200. K and 50.0 kPa
(2) 200. K and 200.0 kPa
(3) 600. K and 50.0 kPa
(4) 600. K and 200.0 kPa
*Which list of the phases of H2O is arranged in order of increasing entropy?
(1) ice, steam, and liquid water
(2) ice, liquid water, and steam
(3) steam, liquid water, and ice
(4) steam, ice, and liquid water
*Which of these changes produces the greatest increase in entropy?
(1) CaCO3(s)  CaO(s) + CO2(g)
(2) 2 Mg(s) + O2(g)  2 MgO(s)
(3) H2O(g)  H2O(l)
(4) CO2(g)  CO2(s)
SKILL #2:
- refer to your notes &amp; RB p. 10
10. Which sample at STP has the same number of molecules as 5 liters of NO2(g) at STP?
(1) 5 grams of H2(g)
(2) 5 liters of CH4(g)
(3) 5 moles of O2(g)
(4) 5 x 1023 molecules of CO2(g)
11. At the same temperature and pressure, 1.0 liter of CO (g) and 1.0 liter of CO 2 (g) have
(1) Equal volumes and the same number of molecules
(2) Equal masses and the same number of molecules
(3) Different masses and a different number of molecules
(4) Different volumes and a different number of molecules
12. At the same temperature and pressure, which sample contains the same number of moles of
particles as 1 liter of O2 (g)?
(1) 1 L Ne (g)
(2) 0.5 L SO2 (g)
(3) 2 L O2 (g)
(4) 1 L of H2O (l)
13. The table below shows data for the temperature, pressure, and volume of four gas samples.
Which two gas samples have the same total number of molecules?
(1) A and B
(2) A and C
(3) B and C
(4) B and D
SKILL #3:
calculating PRESSURE, VOLUME, OR TEMPERATURE OF A GAS
– refer to your notes &amp; RB p. 11-12
14. Describe the relationship between the temperature and pressure of a gas. Sketch a graph of this
relationship and label the axes. As temperature increases, pressure increases.
15. Describe the relationship between the temperature and volume of a gas. Sketch a graph of this
relationship and label the axes. As temperature increases, volume increases.
16. Describe the relationship between the volume and pressure of a gas. Sketch a graph of this
relationship and label the axes. As volume increases, pressure decreases.
17. As the pressure on a sample of gas increases at constant temperature, the volume of the gas
(1) Increases
(2) Decreases
(3) Remains the same
18. As the pressure on a given sample of gas increases at constant temperature, the mass of the
sample
(1) Increases
(2) Decreases
(3) Remains the same
19. A sample of gas A was stored in a container at a temperature of 50&ordm;C and a pressure of 0.50
atmosphere. Compared to a sample of gas B at STP, gas A had a
(1)
(2)
(3)
(4)
Higher temperature and a lower pressure
Higher temperature and a higher pressure
Lower temperature and a lower pressure
Lower temperature and a higher pressure
Use the Combined Gas Law equation to answer the following questions. Remember to convert
temperatures to Kelvin before plugging into the equation! Also, if volume, pressure, or temperature is
“kept constant” or “remains the same”, you can leave it out of the equation. SHOW YOUR WORK and
20. Air bags are an important safety feature in modern automobiles. An air bag is inflated in
milliseconds by the explosive decomposition of NaN3(s). The decomposition reaction produces
N2(g), as well as Na(s), according to the unbalanced equation below.
_2__ NaN3(s) → _2__ Na(s) + __3_ N2(g)
(a) Balance the above equation using the smallest whole-number coefficients.
(b) When the air bag inflates, the nitrogen gas is at a pressure of 1.30 atmospheres, a temperature
of 301 K, and has a volume of 40.0 liters. Calculate the volume of the nitrogen gas at STP.
(1.30 atm)(40.0L)
301 K
=
(1atm) X
273 K
X = 47.2 L
21. What volume will a gas occupy if the pressure on 244 cm3 gas at 4.00 atm is increased to 6.00
atm? Assume the temperature remains constant.
(4.00 atm)(244 cm3)
=
(6.00 atm) X
X = 163 cm3
22. A sample of gas occupies a volume of 50.0 milliliters in a cylinder with a movable piston. The
pressure of the sample is 0.90 atmosphere and the temperature is 298 K. What is the volume of
the sample at STP?
(0.90 atm)(50.0mL) = (1atm) X
X = 41 mL
298 K
273 K
23. A weather balloon has a volume of 52.5 liters at a temperature of 295 K. The balloon is released
and rises to an altitude where the temperature is 252 K.
(a) How does this temperature change affect the gas particle motion?
The particles move more slowly because the temperature decreases.
(b) The original pressure at 295 K was 100.8 kPa and the pressure at the higher altitude at 252 K
is 45.6 kPa. Assume the balloon does not burst. In the space below, show a correct
numerical setup for calculating the volume of the balloon at the higher altitude.
(100.8 kPa)(52.5 L) = (45.6 kPa) X
295 K
252 K
(c) What Celsius temperature is equal to 252 K?
K = C + 273
252 = C + 273
252 – 273 = C = -21 &deg;C
(d) What pressure, in atmospheres (atm), is equal to 45.6 kPa?
1 atm = 101.3 kPa
X = 0.450 atm
X atm
45.6 kPa
24. Divers get “the bends” if they come up too fast because gas in their blood expands, forming
bubbles in their blood. If a diver has 5.0 mL of gas in his blood under a pressure of 250. atm, then
rises instantaneously to a depth where his blood has a pressure of 50.0 atm, what will the volume
of gas in his blood be?
(250. atm)(5.0 mL) = (50.0 atm) X
X = 25 mL
25. Atmospheric pressure on the peak of Mt. Everest can be as low as 0.197 atm, which is why
climbers need to bring oxygen tanks for the last part of the climb. If the climbers carry 10.0 liter
tanks with an internal gas pressure of 23.8 atm, what will be the volume of the gas when it is
released from the tanks?
(23.8 atm)(10.0 L) = (0.197 atm) X
X = 1,210 L
26. On hot days, you may have noticed that potato chip bags seem to “inflate”, even though they
have not been opened. If a 250 mL bag at a temperature of 19 0C is left in a car which has a
temperature of 610 C, what will the new volume of the bag be?
250 mL = X
X = 286 mL
292 K
334 K
27. Some students believe that teachers are full of hot air. If I inhale 2.2 liters of gas at a temperature
of 180 C and it heats to a temperature of 380 C in my lungs, what is the new volume of the gas?
2.2 L =
X
X = 2.4 L
291 K
311 K
28. The total pressure inside a 1.60 L cylinder kept at 35&ordm;C is 1.15 atm. If the volume of the cylinder
drops to 0.75 L and the temperature remains the same, what is the final pressure inside the
cylinder?
(1.15 atm)(1.60 L)
=
X (0.75 L)
X = 2.5 atm
29. A gas has a pressure of 120. kPa, a temperature of – 30.0&ordm;C, and a volume of 50.0 mL. What
volume will the gas have at a pressure of 60.0 kPa and a temperature of 35.0&ordm;C?
30. The pressure inside a 3.0 L cylinder at 25&ordm;C is 0.85 atm. If the pressure is increased to 5.0 atm while
the volume is kept constant, what is the new temperature inside the cylinder?
31. The total pressure inside a 2.0 L container at 28&ordm;C is 1.03 atm. If the temperature is lowered to 0&ordm;C
while the volume remains the same, what is the new pressure inside the cylinder?
32. The volume of a gas in a cylinder is 6.2 milliliters and its pressure is 1.4 atmospheres. The piston is
pushed in until the gas volume is 3.1 milliliters while the temperature remains constant. Calculate
the final pressure after the change in volume.
33. A balloon has a volume of 25 mL at 25&ordm;C and 1.2 atm. Calculate its volume at STP.
34. A sample of helium gas is in a closed system with a movable piston. The volume of the gas sample
is changed when both the temperature and the pressure of the sample are increased. The table
below shows the initial temperature, pressure, and volume of the gas sample, as well as the final
temperature and pressure of the sample.
(a)
(b)
(c)
(d)
Calculate the final volume of the helium gas sample.
Convert the final temperature of the helium gas sample to degrees Celsius.
What pressure, in kilopascals, is equal to 7.0 atmospheres?
Compare the total number of gas particles in the sample under the initial conditions to the
total number of gas particles in the sample under the final conditions.
35. Cylinder A contains 22.0 grams of CO2(g) and cylinder B contains N2(g). The volumes, pressures,
and temperatures of the two gases are indicated under each cylinder.
a.) What is the total number of moles of CO2(g) in cylinder A? 
moles = given mass/GFM
moles = 22.0 / 44 = 0.50 mol
b.) Explain why the number of molecules of N2(g) in cylinder B is the same as the number of
molecules of CO2(g) in cylinder A. 
Avogadro’s law – equal volumes of gases under the same conditions of temperature and
pressure contain equal numbers of particles.
c.) The temperature of the CO2(g) is increased to 450. K and the volume of cylinder A remains
constant. In the space below, show a correct numerical setup for calculating the new
pressure of the CO2(g) in cylinder A. 
1.0 = X
300.
450.
36. A rigid cylinder is fitted with a movable piston. The cylinder contains a sample of helium gas,
He(g), which has an initial volume of 125.0 milliliters and an initial pressure of 1.0 atmosphere, as
shown below. The temperature of the helium gas sample is 20.0&deg;C.
(a) Express the initial volume of the helium gas sample, in liters. 0.125 L
(b) The piston is pushed further into the cylinder. Show a correct numerical setup for calculating
the volume of the helium gas that is anticipated when the reading on the pressure gauge is
1.5 atmospheres. The temperature of the helium gas remains constant.
(1.0)(125) = (1.5)(X)
(c) Helium gas is removed from the cylinder and a sample of nitrogen gas, N2(g), is added to the
cylinder. The nitrogen gas has a volume of 125.0 milliliters and a pressure of 1.0 atmosphere at
20.0&deg;C. Compare the number of particles in this nitrogen gas sample to the number of
particles in the original helium gas sample. Both samples have the same number of particles.
37. The balanced equation below represents the reaction between magnesium metal and
hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas.
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
A piece of Mg(s) has a volume of 0.0640 cubic centimeters. This piece of Mg(s) reacts completely
with HCl(aq) to produce H2(g). The H2(g) produced has a volume of 112 milliliters and a pressure of
1.00 atmosphere at 298 K.
(a) The volume of the piece of Mg(s) is expressed to what number of significant figures? 3
(b) Show a correct numerical setup for calculating the volume of the H 2(g) produced if the
conditions are changed to STP.
112 mL = X
298 K
273 K
SKILL #4:
applying THE IDEAL GAS LAW