Gas Law Review
Equations:
Ideal gas law: PV=nRT
Initial-Final problems:
P1V1 = P2V2
n1T1 n2T2
R= 0.0821 L-atm/mol-K
Density and Molar mass from Idel gas Law: D= P(M)
RT
Dalton’s Law of Partial Pressures: Ptot = Pa + Pb + Pc …
Mole Fraction of gases and pressure: a = na = Pa
ntot Ptot
Graham’s Law of Effusion:
Root mean square velocity:
R = 8.314 J/mol-K
1. A sample of air at 742 mm Hg and 28.5 °C occupies 12.48 L. The conditions are changes to 785 mm
Hg and 42.6 °C. (Assume that the number of molecules remains constant.)
a. Solve the Ideal Gas Law for the three variables in this problem.
b. Find the new volume.
2. 494.5 mL gas sample at 682.4 mm and 86.5 °C has a mass of 0.543 g
a.
b.
c.
d.
What is the equation that was derived from the ideal gas equation that solves for density?
What is the molar mass from the information given. SHOW WORK!!!
What fraction expresses the pressure of the above sample in atm?
Find the molar mass of the gas sample.
3. Butane, C4H10, is a gas at 82 °C and 0.985 atm.
a. Write a balanced equation showing the complete combustion of Butane.
b. What is the mole ratio of C4H10 to O2 from (a)?
c. What volume of oxygen is needed to completely burn 4.68 L of C4H10? (Assume both
Butane and Oxygen are at the conditions given above.)
4. Two flasks are connected with a stopcock. The first flask has a volume of 5.0 L and contains
nitrogen gas a at a pressure of 0.75 atm. The second flask has a volume of 8.0 L and contains
oxygen gas at a pressure of 1.25 atm. When the stopcock between the flasks is opened and the
gases are free to mix, what will the pressure be in the resulting mixture?
5. 24.3 ml of hydrogen gas was collected over water at 16oC and 756.2 mm Hg.
a. Find the partial pressure of the dry gas at these conditions.
b. How many moles of Hydrogen gas were collected?
c. What volume would the dry gas occupy at 1.00 atm (assume constant temperature)?
6. 3.698 g of Oxygen, 4.964 g Carbon Dioxide, and 0.0239 mol of Argon exist in a container at a
pressure of 658.0 mm Hg.
a.
b.
c.
d.
e.
What is the math relationship between Mole, total pressure and partial pressure?
Find moles of each gas.
Set up the mole fraction for each gas.
Find the partial pressure of each gas.
What is the sum of the partial pressures?
7. GIVEN: C2H2 + 3 O2 and 46 °C.
a. How many moles of Oxygen are needed to react with the C2H2?
b. Solve the “Ideal” Gas Law for volume.
c. Find the volume of Oxygen at the conditions given above that will be needed to burn the
2.459 g. of C2H2.
8. A real gas would act most ideal at
a) 1.0 atm and 273 K
b) 10 atm and 546 K
c) 10 atm and 273 K
d) 0.5 atm and 546 K
e) 0.5 atm and 273 K
9. The pressure of 4.0 L of an ideal gas in a flexible container is decreased to one-third of its original
pressure and its absolute temperature is decreased by one-half. The volume then is
a) 1.0 L b) 4.0 L c) 6.0 L d) 8.0 L e) 24 L
10. A given mass of gas in a rigid container is heated from 100 C to 300 C. Which of the following best
describes what will happen to the pressure of the gas? The pressure will…
a)
b)
c)
d)
decrease by a factor of three.
increase by a factor of three.
increase by a factor less than three.
decrease by a factor greater than three.
11. As the average kinetic energy of the molecules of a sample increases, the temperature of the sample
a) decreases
c) remains the same
b) increases
12. If a gas that is confined in a rigid container is heated, the pressure of the gas will…
a) increase
c) remain the same
b) decrease
13. If a gas has a pressure of 2.0 atm, which one of the following equations will express its pressure after...
• the number of moles has been increased to three times the original amount,
• the absolute temperature (K) has been reduced to half, and
• the volume has been tripled?
1 2 4
a) P2 = 2.0 atm x 3 x 1 x 1
3 1 1
b) P2 = 2.0 atm x 1 x 2 x 3
3 2 1
c) P2 = 2.0 atm x 1 x 1 x 3
1 1 3
d) P2 = 2.0 atm x 3 x x 1
4
14. At STP, it was found that 1.12 L of a gas had a mass of 2.78 g. Its molar mass is
a) 2.78 g/mol
c) 55.6 g/mol
b) 27.8 g/mol
d) 111 g/mol
15. At a given temperature, gaseous ammonia molecules (NH3) have a velocity that is ____ gaseous sulfur
dioxide molecules (SO2).
a) greater than
b) less than
c) equal to
d) more inf. needed
16. The ratio of the average velocities of SO2(g) to CH4(g) at 300 K is
a) 1:4
b) 1:2
c) 4:1
d) 2:1
18. Which statement best explains why a confined gas exerts pressure?
a) the molecules are in random motion
b) the molecules travel in straight lines
c) the molecules attract each other
d) the molecules collide with the container walls
19. CH4 gas and O2 gas are together in a container. Which statement correctly describes the velocities
of the two molecules.
a) The two molecules have the same average velocity.
b) The CH4 is moving twice as fast as the O2.
c) The CH4 is moving faster, but not twice as fast as the O2.
d) The O2 is moving faster than the CH4.