eLFH - Kinetic Theory of Gases

Question 1

Definition of kinetic theory of gases

Answer 1

Model of gas behaviour at molecular level that arises from 4 postulates.

Describes characteristics of an imaginary, ideal gas.

Question 2

Postulate 1 of kinetic theory of gases

Answer 2

Gases consist of a large number of particles - either atoms or molecules

Particles treated as point masses which are very far apart in a gas

Therefore volume of particles in a gas is negligible compared to total volume of the gas

Question 3

Postulate 2 of kinetic theory of gases

Answer 3

Individual particles move in random directions and at random speeds

Question 4

Postulate 3 of kinetic theory of gases

Answer 4

Individual particles travel in straight lines between abrupt collisions with other particles, objects or walls of a container

Collisions are perfectly elastic so total kinetic energy does not change during the collision

Question 5

Postulate 4 of kinetic theory of gases

Answer 5

There are no attractive or repulsive forces between the particles

Would be a breach of postulate 3 if they did as it would involve a loss of kinetic energy and particles would change phase eg to liquid / solid

Question 6

How do real gases deviate from behaviour of the imaginary ideal gas

Answer 6

Real gas particles occupy a small but finite volume

Gas particles exhibit attractive forces for one another especially when particles are close together eg at low temperatures or high pressures

Therefore real gases are affected by their surrounding conditions

Question 7

Brownian motion

Answer 7

Provides demonstration that fluids consist of fast moving particles

Particles suspended within a medium (liquid or gas) with move randomly as a result of the random movement of fast moving particles withing the suspension medium

Question 8

Maxwell-Boltzmann distribution

Answer 8

Mathematical description / graphical illustration of the distribution of probability that any random gas particle will have a given speed

Question 9

Effect of temperature on Maxwell-Boltzmann distribution and implication on gas particles

Answer 9

As heat energy is added, manifests as increase in kinetic energy of gas particles and average speed increases

Therefore peak of graph shifts to right

Area of curve remains constant as the sum of probability distributions is always one

Therefore temperature is a reflection of average kinetic energy of particles of a gas

Question 10

Kinetic energy formula

Answer 10

Kinetic energy = 1/2 x mass x speed^2

Question 11

Implication of kinetic energy formula

Answer 11

Gases with higher molecular weight (and therefore mass) will have slower average speed for a given kinetic energy

Therefore at a given temperature, gases with higher molecular weight will have speed distributions shifted to the left, and lower molecular weights shifted to the right

Question 12

Force (and Pressure) changes as explained by kinetic theory

(Linked with later flashcard “How increase in pressure is generated according to kinetic theory explanations for a gas within a container”)

Answer 12

Example of particle colliding with wall of container at right angles with speed of “x”

Perfectly elastic collision

Velocity (which is speed with direction) changes from +x to -x (total change of 2x)

Acceleration is rate of change of velocity - therefore particle undergoes acceleration

Force = mass x acceleration (mass remains constant, therefore force increases with increased acceleration)

Pressure is cumulative force generated divided by total area over which that force is applied

Question 13

How increase in pressure is generated according to kinetic theory explanations for a gas within a container

(Linked with previous flashcard “Force (and Pressure) changes as explained by kinetic theory”)

Answer 13

Pressure is cumulative force generated divided by total area over which that force is applied so increased pressure generated by either:

Increasing frequency of collisions of gas particles with the container walls

OR

Reducing area over which collisions occur

Question 14

Boyle’s Law

Answer 14

At constant temperature, as volume of gas is decreased, its pressure will increase

Question 15

Charles’ Law

Answer 15

At constant pressure, the volume of gas varies directly with the absolute temperature

Question 16

Gay-Lussac’s Law

Answer 16

At constant volume, the absolute pressure of a given mass of gas varies directly with the absolute temperature