Ch. 8: The Gas Phase

Question 1

What is the mathematical relationship between all the units for pressure?

Answer 1

1 atm = 760 mmHg = 760 torr = 101.325 kPa

Question 2

What is STP?

Answer 2

Standard temperature and pressure = 273K, 1 atm

Question 3

Is the pressure on top of a mountain higher or lower than on regular ground?

Answer 3

Lower

Question 4

What is an ideal vs real gas?

Answer 4

Ideal: a hypothetical gas with molecules that have no intermolecular forces and occupy no volume

Real: display intermolecular forces and occupy volume, they deviate from ideal behavior under high pressures and low temperatures

Question 5

What is the ideal gas law equation?

Answer 5

PV=nRT

Question 6

What is density?

Answer 6

mass per unit volume of a substance

Question 7

How is density mathematically related to the ideal gas law?

Answer 7

PV = nRT
n = m (g) / molar mass (g/mol)
PV = (m/M)RT
PM = (m/V) RT
PM/RT = density

density = m/V

Question 8

How many liters does 1 mole of a gas at STP occupy?

Answer 8

22.4 L

Question 9

What is Avogadro’s principle?

Answer 9

All gases at constant temperature and pressure occupy volumes directly proportional to the number of moles of gas present. As the # of moles of gas ↑, volume ↑ proportionally.

Question 10

What is Boyle’s Law?

Answer 10

At constant temperature, the volume of a gas is inversely proportional to its pressure.

P₁V₁ = P₂V₂

Question 11

What is Charles’s Law?

Answer 11

At constant pressure, the volume of a gas is proportional to its absolute temperature.

V₁/T₁ = V₂/T₂

Question 12

What is the combined gas law equation?

Answer 12

P₁V₁/T₁ = P₂V₂/T₂

Question 13

What is Dalton’s law of partial pressures? Equations?

Answer 13

The total pressure of a gaseous mixture is equal to the sum of the total partial pressures of the individual components.

P(total) = Pa + Pb + Pc + …

Pa = Xa * P(total)

Question 14

What is a mole fraction?

Answer 14

Xa = moles of gas a / total moles of gas

Question 15

How does the partial pressure of a gas affect it’s solubility?

Answer 15

As the partial pressure of a gas INCREASES, the solubility of the gas INCREASES.

Question 16

How does the molar concentration of gas mathematically relate to pressure? What does this relationship tell us?

Answer 16

[A]₁ / P₁ = [A]₂ / P₂

This shows the solubility (mol/L) increases as pressure increases.

Question 17

What equation relates kinetic energy and temperature?

Answer 17

KE = 3/2 (KB) T

KB = boltzman constant

Question 18

What is the relationship between particle speed and temperature?

Answer 18

The higher the temperature, the faster the molecules move. The larger the molecules, the slower they move.

Question 19

What is Graham’s Law? Equation?

Answer 19

Under constant temperature and pressure, the rates at which two gases diffuse are inversely proportional to the square roots of their molar masses.

r₁/r₂ = sqrt (M₂/M₁)

r is the diffuse rate
M is molar mass

The larger the molar mass, the slower the diffusion rate.

Question 20

What is the difference between effusion and diffusion?

Answer 20

Diffusion is the mixing of gases.

Effusion is the the movement of gas particles through a small hole under pressure.

Question 21

What conditions cause gases to deviate from ideal conditions?

Answer 21

Low temperature
High pressure (low volume)

Question 22

How does high pressure cause a gas to deviate from ideal to real?

Answer 22

As pressure increases, volume decreases. This causes particles to get pushed closer together. They start to take up a larger volume than would be predicted by the ideal gas law.

Question 23

How does low temperature cause a gas to deviate from ideal to real?

Answer 23

As temperature decreases, the average speed of gas molecules decreases and the attractive intermolecular interactions become more significant.

Question 24

What do “a” and “b” represent in the van der waals equation of state?

Answer 24

“a” corrects for ATTRACTIVE FORCES between molecules. It is largest for large polar gases since they will display more intermolecular interactions.

“b” corrects for the VOLUME of the gas molecules. Larger molecules have a larger b.