gen chem- Gases

A 1.0 L container at 25^oC is filled with 1.0 mole of He and 2.0 moles of Ne. Assuming that both gases behave ideally, which of the following statements is true?

A. molecules of He travel faster than molecules of Ne

B. the two gasses have the same pressure

C. the gas molecules of Ne have a higher average kinetic energy than those of He

D. molecules of Ne occupy twice as much volume as molecules of He

A

• the speed of a gas molecule is directly proportional to its temp and inversely proportional to its molar mass

• since He has a lower molar mass, its molecules will travel faster than those of Ne at the same temp

• B- Ne pressure will be twice that of He

• C- the avg kinetic energy of gas molecules depends only on temp, they are at the same temp, so same avg kinetic energy

• D- both gases are in same container; gases in a container will expand to occupy the entirety of the container, so both gasses occupy the same volume

A flask contains 5.5 mol of O₂ gas at 25^oC and 2.00 atm. How much O₂ gas, in moles, must be added to increase the pressure to 8.00 atm at constant temperature and volume?

A. 2.0 mol

B. 5.5 mol

C. 11.5 mol

D. 9.0 mol

E. 16.5 mol

E

P1 / n1 = P2 / n2

(2) / (5.5) = (8) / x

2x = 44.0

x = 22 mol

22-5.5= 16.5

A mixture of gas is composed of 1.0 mol He, 2.0 mol Ar, and 1.5 mol of Cl₂. What is the partial pressure of Cl₂ in the mixture if the total pressure is 3 atm?

A. 0.33 atm

B. 0.5 atm

C. 1 atm

D. 1.5 atm

E. 3 atm

C

partial pressure = mole fraction (x1) x total pressure (Pt)

x1 = # of moles / total # moles

x1 of Cl2 = 1.5 / 4.5 = 1/3

partial pressure = (1/3) x 3 = 1

If gases X and Y have the same number of molecules and are at the same temperature, what will the volume of gas X be if its pressure is one-third of gas Y’s pressure?

A. triple that of gas Y

B. double that of gas Y

C. the same as that of gas Y

D. one-half that of gas Y

E. one-third that of gas Y

A

• the pressure of an ideal gas is inversely proportional to its volume when all other factors are kept the same

• Boyle’s law

A 3.0 mol sample of an ideal gas at 27 °C and 5.0 atm is deposited into a rigid 1.0 L container. What is the new temperature of the gas if the pressure is increased to 8.0 atm?

A. 30°C

B. 43°C

C. 207°C

D. 316°C

E. 480°C

C

Which of the following statements correctly describes a property of gases? 

A. they are excellent conductors of heat

B. they exert pressure on the walls of the container they are contained in

C. they more in a nonrandom motion

D. they occupy less volume than the solids from which they form

B

Gas A has a molar mass of 4 g/mol and gas B has a molar mass of 36 g/mol. If the gases are at the same temperature, what will be the rate of effusion of gas B relative to gas A?

A. rate of gas B = 1/9 x rate of gas A

B. rate of gas B = 1/4 x rate of gas A

C. rate of gas B = 1/3 x rate of gas A

D. rate of gas B = 3 x rate of gas A

E. rate of gas B = 9 x rate of gas A

C

rate b / rate a = square root ( MMA / MMB)

rate b / rate a = square root (4 / 36) = square root (1 / 9) = 1/3

If a mixture of helium and argon contains 2 moles of He_(g) and 3 moles of Ar_(g) and the total pressure is 250 kPa, what is the partial pressure of He_(g)?

A. 40 kPa

B. 60 kPa

C. 100 kPa

D. 150 kPa

E. 250 kPa

C

• partial pressure = gas’s mole fraction x total partial pressure

  mole fraction of He = 2 / 5

• pp = (2/5) x 250 = 500 / 5 = 100

Which statement best describes Charles's law?

A. a gas’s rate of effusion is inversely proportional to the square root of molar mass

B. at constant pressure, volume and temperature are directly proportional

C. total pressure is equivalent to the sum of individual partial pressures

D. volume and moles of gas are directly proportional to each other

E. volume and pressure are inversely related to each other

B

A- Graham’s Law

C- Dalton’s Law

D- Avogadro’s Law

E- Boyle’s Law

Under which of the following conditions would a real gas be least likely to behave as an ideal gas?

A. very low temperature

B. very large container volume

C. very low intermolecular attractions

D. very low pressure

E. very small particle volume

A

• it’s asking LEAST likely

• gasses behave more ideally at high temps, large volumes, low pressures, and small molecular sizes

Which of the following is true regarding gases found at equal volume and temperature? 

A. the two gases have the same entropy

B. the two gases have the same average speed

C. helium exerts greater pressure than argon

D. the two gases have the same enthalpy

E. the two gases have the same average kinetic energy

E

A closed chamber of gas at a constant temperature undergoes the following reaction at 30,000 kPa:

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l)

Assuming 1 mol of propane gas and 5 mol of oxygen gas are used in the reaction, what is the approximate resulting pressure (kPa) after the reaction occurs?

A. 15,000

B. 30,000

C. 35,000

D. 60,000

E. 70,000

A

P1 / n1 = P2 / n2

30,000 / 6 = x / 3

30,000 × 3 = 6x

90,000 = 6x

x = 15,000

Which of the following represents the rate of effusion of hydrogen gas to oxygen gas? 

A. 1/8

B. ½

C. ¼

D. 2

E. 4

E

rate H / rate O = square root (MMO / MMH) = square root (32 / 2) = square root (16) = 4

The volume of one mole of an ideal gas at 25 °C is

A. 22.4 L

B. directly proportional to pressure and temp

C. inversely proportional to pressure and temp

D. directly proportional to pressure and inversely proportional to temp

E. inversely proportional to pressure and directly proportional to temp

E

Which of the following gases will have the greatest density at STP?

A. F₂

B. Cl₂

C. P

D. O₂

E. Kr

E

• the density of a gas is directly proportional to its molar mass

• Kr has the highest mass and therefore the highest density