Kinetic Theory of Gases

Question 1

The four postulates of an ideal gas include (true or false):

A real gas approximates to the behaviour of an ideal gas

Answer 1

False. Although this is a true statement in itself, it is not one of the four postulates.

Question 2

The four postulates of an ideal gas include (true or false):

Gases consist of a number of particles

Answer 2

True

Question 3

The four postulates of an ideal gas include (true or false):

Relative to their size, the particles are very close together

Answer 3

False. They are very far apart; the space between each particle is very much larger than the particle itself.

Question 3

The four postulates of an ideal gas include (true or false):

The particles move in a random pattern

Answer 3

True

Question 4

The four postulates of an ideal gas include (true or false):

There are no attractive or repulsive forces between particles

Answer 4

True

Question 4

The four postulates of an ideal gas include (true or false):

The particles collide with one another

Answer 4

True

Question 4

The particles of a real gas (true or false):

Have a negligible volume

Answer 4

False. Real gases have particles that occupy a small but absolute volume.

Question 5

The particles of a real gas (true or false):

Are in constant random motion

Answer 5

True

Question 6

The particles of a real gas (true or false):

Do not stick together or change phase

Answer 6

False. This may occur due to the finite forces of attraction between particles of a real gas.

Question 7

The particles of a real gas (true or false):

Have forces of attraction for each other

Answer 7

True

Question 8

The particles of a real gas (true or false):

Deviate most from an ideal gas when the particles are far apart from one another

Answer 8

False. The deviation in behaviour of a real gas from an ideal gas is greatest when the particles are close together, such as at low temperatures or when under high pressure.

Question 9

With regard to the postulates of the kinetic theory of gases (true or false):

The particles of a gas are in constant motion

Answer 9

True

Question 10

With regard to the postulates of the kinetic theory of gases (true or false):

All the particles within a gas, at a fixed temperature, will be moving at the same speed

Answer 10

False. Particles move at a range of speeds, governed by the Maxwell-Boltzmann distribution.

Question 11

With regard to the postulates of the kinetic theory of gases (true or false):

The volume of gas particles relative to their container is small, but not negligible

Answer 11

False. Although this statement is true for real gases, the kinetic theory describes an ideal gas with negligible molecular volume.

Question 12

With regard to the postulates of the kinetic theory of gases (true or false):

Gas particles collide frequently with the walls of their container, but not with each other, as the attractive forces between molecules would result in them sticking to one another

Answer 12

False. Particles collide in a perfectly elastic manner between each other and with the walls of their container. There are no attractive or repulsive forces between particles in the ideal gas described by the kinetic theory.

Question 13

With regard to the postulates of the kinetic theory of gases (true or false):

Particles travel in straight lines between collisions

Answer 13

True

Question 14

The speed of gas particles (true or false):

Varies inversely with temperature

Answer 14

False. The speed and kinetic energy of gas particles will increase with temperature.

Question 15

The speed of gas particles (true or false):

Is distributed normally

Answer 15

False. The speeds are distributed normally with a right skew.

Question 16

The speed of gas particles (true or false):

With greater mass, is faster on average than those with smaller mass at a given temperature

Answer 16

False. Gases with a higher molecular weight have a lower average speed at a given temperature than a gas of lower molecular weight.

Question 17

The speed of gas particles (true or false):

Has a distribution that shifts to the left as molecular weight increases

Answer 17

True. At a given temperature, a gas of higher molecular weight has particles moving at a lower average speed. The peak of the Maxwell-Boltzmann curve is therefore further to the left than the curve for a gas of a lower molecular weight.

Question 18

The speed of gas particles (true or false):

Is directly proportional to the kinetic energy of those particles

Answer 18

False. Kinetic energy varies with the square of the speed and is governed by the relationship

Ek = 1/2mv2 (squared)

Question 19

The temperature of a gas (true or false):

Reflects the average potential energy of the gas particles

Answer 19

False. Temperature is a reflection of the average kinetic energy of the gas particles.

Question 20

The temperature of a gas (true or false):

Falls as heat energy is removed from the gas

Answer 20

True

Question 21

The temperature of a gas (true or false):

When rising, causes the distribution of the speed of the gas particles to shift to the left

Answer 21

False. As the temperature rises, the distribution of the speeds of the gas particles shifts to the right.

Question 21

The temperature of a gas (true or false):

Varies directly with the average speed of the gas particles

Answer 21

False. Temperature reflects the average kinetic energy which varies directly with the square of the average speed of the particles.

Question 22

The temperature of a gas (true or false):

When rising, causes the rate of molecular collisions with the container walls to increase

Answer 22

True. As temperature rises the average speed of the particles will increase, resulting in more frequent collisions with the container walls and with other particles.

Question 23

The pressure of an ideal gas (true or false):

Increases in a fixed container, if the kinetic energy of the particles increases

Answer 23

True. As the kinetic energy increases, so too does the average speed of the gas particles. Therefore they collide more frequently with the sides of the container resulting in an increase in pressure.

Question 24

The pressure of an ideal gas (true or false):

Falls if the volume of the container is decreased, as the gas particles have a smaller surface area to collide with

Answer 24

False. As the volume of the container decreases, particles collide more frequently with the walls and the pressure therefore rises.

Question 25

The pressure of an ideal gas (true or false):

Relies on the constant motion of its particles

Answer 25

True. The constant motion of the gas particles leads to repeated collisions with the walls of the container. These collisions impart momentum which exerts a measurable force.

Question 26

The pressure of an ideal gas (true or false):

Rises with temperature by virtue of a rise in the average kinetic energy of the gas particles, leading to more frequent collisions with the container walls

Answer 26

True. A rise in kinetic energy results in an increase in average speed of the gas particles. This leads to an increase in the frequency of collisions with the container walls and, therefore, an increase in pressure.

Question 27

The pressure of an ideal gas (true or false):

Remains constant as temperature rises, only if the container is not allowed to expand

Answer 27

False. The container must be allowed to expand, otherwise the pressure increases with temperature due to more frequent collisions with the container walls.