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Question 1

Gas pressure (p)

Answer 1

the force exerted per unit area by the gas on the
walls of its container.

Question 2

Barometer:

Answer 2

device used to measure atmospheric pressure

Question 3

pascal (pa)

Answer 3

SI unit for gas, also used: mm Hg, atm, bar

1 atm = 760 mm Hg
1 Pa = 1 N m-2

1 bar = 1 × 105 Pa = 1 × 102 kPa = 0.9872 atm

Question 4

Other Gas properties

Answer 4

Temperature (T), Volume (V), Amount (n)

Question 5

Ideal Gas Equation

Answer 5

“Ideal gas” assumptions:
– The molecules of the gas have zero volume.
– There are no interactions between gas molecules.

pV = nRT

R = 8.314 L kPa K-1 mol-1

Limitations
– Pressure is about 1 bar or less.
– Temperature is at or above 25°C.

Question 6

Gas Constant

Answer 6

R=8.314 L kPa K-1 mol-1
R=8.314 m3 Pa K-1 mol-1
R=0.08206 L atm K-1 mol

1 Pa = 1 Nm-2 = 1 kg m-1 s-2 = 1 Jm-3
R=8.314 m3 Pa K-1 mol-1 = 8.314 J K-1 mol-1

Question 7

Gas Density

Answer 7

pV = (m/M) RT

density = m/V = pM/RT

Question 8

Partial pressures

Answer 8

the pressure each gas in a mixture would exert if it were the only gas in a container of the same size at the same temperature.

• Dalton’s law of partial pressures:
  ptotal = pA + pB + pC + ….
  (Where PA, PB, PC are the partial pressures of each component gas)

in a mixture of gases:
p(total) = n (total) (RT/V)

Question 9

mole fraction (x)

Answer 9

the amount of a particular component in a mixture, divided by the total amount of all components present.

X (A) = n (A) / n (A) + n (B) + n(C)
= n (A) / n (total)

• The partial pressure for one component can then be calculated using:

pA = x(A)p(total)

Question 10

The Kinetic-Molecular Theory of Gases

Answer 10

1. Gases consist of particles. At reasonably low pressures and high temperatures, forces between the particles are negligible.
2. The particles of a gas are in continual, random, and rapid motion.
3. Gas particles move in straight lines unless they collide with each other or the walls of their container. These collisions take place without loss of the total energy of the system
4. The average kinetic energy of gas particles is proportional to the gas temperature. All gases, regardless of their molecular mass, have the same average kinetic energy at the same temperature.

Question 11

Molecular Speed Depends on the Temperature

Answer 11

• At a given temperature, the most probable speed corresponds to the maximum in the curve.
• As the temperature increases, the most probable speed increases, as does the number of fast-moving molecules.

Question 12

Kinetic Energy

Answer 12

E(k) = 1/2 (mass)(speed) ^2 = 1/2(m)(u)^2

The average kinetic energy relates to the average speed of a collection of molecules, and is directly proportional to temperature.

E (k) = 3/2 (kT)

u = sqrt (3RT/M)

Question 13

Gas Relationships

Answer 13

Gas pressure from collisions = total force due to collisions / area

• p is proportional to T when n and V are fixed: p = (nRT/V)
• p is proportional to n when V and T are constant: p = n(RT/V)
• V is proportional to nT when p is constant: V = nT(R/p)
• p is inversely proportional to V when n and T are constant: p = (1/V)(nRT)

Question 14

Diffusion

Answer 14

the mixing of molecules of two or more gases due to their random molecular motions.

Question 15

Effusion

Answer 15

the movement of gas through a tiny opening in a container into another container where the pressure is very low.

Question 16

Rate of effusion

Answer 16

the amount of each gas passing through a
hole per second

Grahams Law Of Effusion:
Rate of effusion of gas 1 / rate of effusion of gas 2 = sqrt (molar mass of gas 2/molar mass of gas 1)

Question 17

Real gas behaviour:

Answer 17

– The volume occupied by gas molecules is not negligible
– Intermolecular forces are not negligible
– Loss of kinetic energy in collisions between molecules
– Formation of clusters of molecules

Question 18

Kinetic-Molecular Model—Liquids and Solids

Answer 18

The particles in a gas under ambient conditions are far apart, and travel distances of many molecular diameters before undergoing a collision.

The particles in a liquid diffuse across the simulation cell very slowly

The particles in a solid are close together and in an orderly arrangement with a high degree of symmetry. They move around in their lattice positions, but don’t migrate very far under ordinary conditions.

Question 19

Vaporization or evaporation:

Answer 19

the process by which a substance in the liquid state becomes a vapour. A few of the molecules at the surface of a liquid have enough energy and are moving in the right direction to escape the attractions of their neighbours and enter the
gaseous state.

Question 20

Condensation.

Answer 20

At the same time as evaporation is taking place, some molecules in the gaseous state can re-enter the liquid.

Question 21

equilibrium vapour pressure

Answer 21

a measure of the tendency of its molecules to escape from the liquid phase and enter the vapour phase at a given temperature.