Chem. 152
Dr. Saidane
Gases
1. For each of the following example give the appropriate gas property it illustrates:
a) A bicycle tire inflates when you pump air into the valve on one side.
A gas fills the container it occupies. A gas expands.
b) A car is supported on a cushion of air.
A gas is highly compressible.
c) An air mattress springs back to its original shape after being pressed.
Gas can be easily compressed and fills the container it occupies.
d) A balloon filled with air weighs more than an empty balloon.
Gases consists of tiny particles each with mass.
e) The color of a gas is uniform throughout the bottle containing it.
Gases occupy the entire volume of their container. Diffusion
2. The volume of gas particles themselves is assumed to be negligible.
3. Gas molecules are said to be in constant motion.
4. The collisions between gas particles are perfectly elastic.
5. The temperature of a gas is a measure of the average kinetic energy of the gas particles.
6. Gas particles exert no attraction on one another.
7. If the molecular speed of a gas increases, its rate of diffusion will increase.
8. If the temperature of a gas increases, the pressure of the gas will increase.
9. If the molecular mass of a gas increases, the total volume of the gas will remain the same.
10. If the temperature of a gas decreases, the pressure of the gas will decrease.
11. The air pressure for a certain tire is 109 kPa. What is the pressure in atm?
109 kPa / 101.3 kPa = 1.08 atm
12. The air pressure inside a submarine is 0.62 atm. What would be the height of a column of
mercury balanced by this pressure?
0.62 atm x(760 mm /1 atm) = 471 mmHg
13. The weather news gives the atmospheric pressure as 1.07 atm. What is this atmospheric
pressure in mmHg.
1.07 atm x (760 mmHg/1 atm) = 813 mmHg
14. The temperature of a gas is 30C, what is the temperature in Kelvin.
30C + 273 = 303 K
15. What change in weather does a falling barometer indicate? Explain.
Decrease in atmospheric pressure, which is also caused by less air particles hitting the
ground, which means higher temperature as hot air rises up.
16. What exactly causes atmospheric pressure?
Atmospheric pressure is caused by air molecules hitting the ground. The more air
particles, the greater the pressure. This can also be caused by cooler temperature. As the
air molecules, get colder, they move slowly and will be pulled faster to earth by gravity,
causing a greater pressure on the ground.
17. Two similar balloons are filled with helium. One is filled to a volume of two liters and the other
to four liters. In which balloon are the helium molecules moving more rapidly? Explain.
The volume is different in the balloon because of the amount of helium that is doubled in
the four liter balloon. Both will be at the same temperature. The speed of motion is only
caused be the change of temperature, regardless of the amount of particles.
18. Give the name of the scientist for each of the following gas laws as well as the equation:
a) The pressure of a gas is inversely proportional to its volume. Boyle.
b) The sum of the partial pressures of gases in a mixture is equal to the total pressure of the
mixture. Dalton.
c) Equal volumes of gases contain equal numbers of particles. Avogadro.
d) The volume of a gas is directly proportional to its temperature. Charles.
19. Complete the following statements by writing “decreases”, “ increases”, or “remains the same”:
A gas is compressed in a cylinder…
a) The distance between gas molecules decreases.
b) The number of gas molecules stays the same.
c) Its volume decreases.
d) Its pressure increases.
e) Its mass stays the same.
20.
a)
b)
c)
d)
e)
Complete the following sentences by filling the correct numerical value:
Standard temperature is 0 degree Celsius.
Absolute zero is 0 Kelvin.
The volume of 1 mole of gas at STP is 22.4 L.
Standard pressure is equal to 101.3 kPa.
If the pressure of 2 L of a gas at STP doubles, the new volume would be 1 L.
21. A gas occupies a volume of 2.45 L at a pressure of 1.03 atm and a temperature of 293K. What
volume will the gas occupy if the pressure changes to 0.98 atm and the temperature remains
unchanged?
V2 = P1V1 / P2 = 1.03 x 2.45 / 0.98 = 2.58 L
22. The cylinder of a car’s engine has a volume of 0.625 L when the piston is at the bottom of the
cylinder. When the piston is at the top of the cylinder the volume is 0.06 L. If the cylinder is
filled with air at an atmospheric pressure of 765.1 mmHg when the piston is at the bottom, what
is the pressure in units of kPa when the piston is at the top of the cylinder?
Assume temperature remains unchanged.
P2 = P1V1 / V2 = 765.1 x 0.625 / 0.06 = 7970 mmHg x(101.3 kPa/ 760 mm Hg) = 1062 kPa
23. A gas sample at 83C occupies a volume of 1400 L. At what temperature will it occupy 1200 L?
T2 = V2T1 / V1 = (83+273) x 1200 / 1400 = 305 K = 32C
24. A gas occupies 0.105 mL at 100 K. At what Celsius temperature will its volume be 0.140 mL?
Assume the pressure remains constant.
T2 = V2T1 / V1 = 0.140 mL x 100 K / 0.105 mL = 133 K = -140C
25. What is the pressure of a mixture of helium, nitrogen, and oxygen if their partial pressures are
600 mmHg, 150 mmHg, and 102 mmHg?
P = 600 + 150 + 102 = 852 mmHg
26. The barometer shows the atmospheric pressure to be 762 mmHg. What is the partial pressure of
nitrogen if nitrogen makes up 78 % of air?
P (N2) = 0.78 x 762 = 594 mmHg
27. What volume would be occupied by 100 g of oxygen gas at a pressure of 1.5 atm and a
temperature of 25C?
O2 has molar mass 32.00g so 100g = 3.13 mol O2
V= nRT/P = 3.13 mol x 0.0821 x (25+273) K / 1.5 atm = 51 L
28. A balloon is inflated with 0.2494 g of helium to a pressure of 1.26 atm. If the desired volume of
the balloon is 1.25 L, what must the temperature be in C?
Moles He = 0.2494 / 4.003 = 0.06230 moles H
T = PV/nR = 1.26 atm x 1.25 L / 0.06230 mol x 0.0821 = 308 K = 35C
29. How many grams of argon would it take to fill a light bulb with a volume of 0.475 L at STP?
n = PV / RT = 1 atm x 0.475 L / 0.0821 x 273 K = 0.0212 mol Ar
Mass Ar = 0.0212 mol x 39.95 g = 0.847 g
30. A sample of Br2 gas is loaded into an evacuated bottle at STP. The volume of the bottle is 0.25
L. How many moles of Br2 gas will be contained in the bottle?
n = PV / RT = 1 atm x 0.25 L / 0.0821 x 273 K = 0.011 mol B2