Gaseous State

Question 1

Ideal Gas Equation

Answer 1

p (in Pascals) V (in m3) = n (in mol) R (molar gas constant - 8.31) T (in Kelvin [need to plus 273])

Question 2

Basic Assumptions of Kinetic Theory as applied to ideal gas (5)

Answer 2

Ideal gas consists of particles of negligible volume

Gas particles exert negligible attractive forces on one another

Gas particles are in constant random motion (colliding with one another and with container walls)

Collisions between gas particles are perfectly elastic

Average KE of gas particles is proportional to temperature

Question 3

Difference between real gases and ideal gas

Answer 3

Ideal gas particles have negligible volume and exert negligible attractive forces on another, while real gas particles have finite volume and size and have attractive forces between gas particles

Question 4

Why low pressure helps gas to approach ideality and not high pressure?

Answer 4

Low pressure:
- Gas particles far apart
- Gas occupies big volume
- Volume occupied by gas particles can be considered to have negligible volume compared to container volume
- Intermolecular attractive forces between widely spaced gas particles negligible

High pressure:
- Gas particles much closer
- Gas occupies a smaller volume
- Volume of gas particles not negligible as compared to container volume
- Intermolecular attractive forces between closely spaced gas particles are significant

Question 5

Why high temperature helps gas to approach ideality and not low temperature?

Answer 5

High temperature:
- Gas particles possess sufficiently high kinetic energy to overcome intermolecular attractive forces
- Intermolecular attractive forces can be considered negligible

Low temperature:
- Gas particles possess less kinetic energy, insufficient to overcome intermolecular attractive forces
- Intermolecular attractive forces are significant

Question 6

Negative and positive deviations from ideal gas behaviour

Answer 6

At moderately high pressure, pV/ RT <1:
- Volume of system becomes smaller
- Gas particles come closer and intermolecular attractive forces between gas particles become significant
- Gas occupies a volume smaller than ideal, resulting in decreased volume and smaller numerator

At very high pressure, pV/RT > 1:
- Volume of system becomes very small
- Gas particles so close that there is intermolecular repulsive force between electron clouds
- Gas occupies a volume larger than ideal, resulting in increased volume and larger numerator

Question 7

How deviations are amplified?

Answer 7

If there are stronger bonding (pd-pd/ hydrogen bonding compared to weaker id-id interactions): Intermolecular attractive and repulsive forces are greater, greater deviations

If larger Mr:
More electrons, more easily polarised, hence stronger interactions and greater intermolecular attractive and repulsive forces, greater deviations

Question 8

Dalton’s Law of Partial Pressures

Answer 8

The total pressure of a mixture of non-reacting gases is equal to the sum of partial pressures of the individual gases in the mixture.

Question 9

Mole fraction

Answer 9

Ratio of number of moles of gas A to the total number of moles of all components in mixture

Question 10

Vapour pressure definition and correlation

Answer 10

Vapour pressure is pressure exerted by gaseous particles on liquid surface and walls of container

Stronger the intermolecular forces of a liquid, the lower its volatility and higher boiling point, lower saturated vapour pressure