5.3- 5.3.6-Ideal gases

Question 1

How do Molecules in a gas move?

Answer 1

Molecules in a gas are in a constant random motion at high speeds. Random motion means that the molecules are travelling in no specific path and undergo changes when they colide, with the walls of its container and with other molecules

Question 2

What is Brownian motion?

Answer 2

The movement of tiny particles. This provides evidence that air is made of smaller particles larger particles move with a higher motion, this is a result of larger particles colliding with smaller particles that are invisible

Question 3

How does pressure effect particles?

Answer 3

A feature of gases is that they fill their container. Pressure is force per unit area. As the gas particles move about randomly they colide with the walls of their container. These collisions produce a net force at the walls of the gas container. A gas at a high pressure has more frequent collisions with the container walls and a greater force hence higher pressure higher the force exerted per unit area

Question 4

What does the pressure of a gas in a container depend on?

Answer 4

Amount of pressure that a gas exerts on its container is dependent on the tempreture of the gas this is because the particles move with more energy as their particles increases (K.E).
If the tempreture of the gas decreases, th pressure of the container also decreases.

Question 5

What is absolute zero?

Answer 5

Absolute zero is the tempreture where particles are no longer moving and not colliding with each other or the container it is equal to -273 degrees.

Question 6

What is the kelvin scale?

Answer 6

The Kelvin tempreture scale begins at absolute zero (-273). An increase of 1K is the same change as an increase of 1. It is not possible to have a tempreture lower than 0K. It can never be a negative value.

Question 7

What is pressure of a gas related to?

Answer 7

The tempreture of a gas is related to the average speed of the molecules, the hotter the gas, faster the molecules.
Hence the molecules collide with the surface of the walls more frequently. This is because Kinetic energy increases.

Question 8

What does Increase tempreture do to a particle?

Answer 8

Heating a system changes the energy stored in a system by increasing the Kinetic energy of the particles. The Kelvin tempreture of the gas is related to the average Kinetic energy of the molecules. Increase in Kinetic Energy can can cause the tempreture of the system to change or produce a change of state.
Higher temp higher average Kinetic energy of the molecules this means they move and colide quicker.

Question 9

What is internal energy of a gas?

Answer 9

The internal energy of a gas is the sum of the kinetic energy of all the molecules

Question 10

How does tempreture effect Kinetic energy and pressure?

Answer 10

f the temperature of a gas is increased, the particles move faster and gain kinetic energy
Therefore, they will collide more with each other and the container leading to an increase in pressure

Question 11

What is the link between tempreture and average Kinetic energy?

Answer 11

The tempreture is directly proportional to the average kinetic energy of the molecules

Question 12

How can the pressure of a gas change if the tempreture is kept at a constant?

Answer 12

If a gas is compressed this will decrease the volume (area) of the molecules which will increase the pressure.

If a gas is expanded which increases the volume (area) which will decrease the pressure

Question 13

How does a change in pressure cause a change in volume?

Answer 13

A vacuum pump can be used to remove the air from a sealed container

Question 14

What happens when a gas is compressed?

Answer 14

The molecules will hit the walls of the container more frequently this creates an overall large net force on the walls which increases the tempreture

Question 15

How does tempreture effect pressure?

Answer 15

The motion of molecules in a gas changes according to the temperature
As the temperature of a gas increases, the average speed of the molecules also increases
Since the average kinetic energy depends on their speed, the kinetic energy of the molecules also increases if its volume remains constant
The hotter the gas, the higher the average kinetic energy
The cooler the gas, the lower the average kinetic energy
If the gas is heated up, the molecules will travel at a higher speed
This means they will collide with the walls more often
This creates an increase in pressure
Therefore, at a constant volume, an increase in temperature increases the pressure o

Question 16

What is the pressure law?

Answer 16

P ∝ T

This means the pressure is proportional to the temperature

Question 17

What is Boyle’s Law?

Answer 17

For a fixed mass of a gas held at a constant temperature:
pV = constant

Where:
p = pressure in pascals (Pa)
V = volume in metres cubed (m3)

Question 18

Explain the relationship between pressure and volume?

Answer 18

This means that the pressure and volume are inversely proportional to each other
When the volume decreases (compression), the pressure increases
When the volume increases (expansion), the pressure decreases
This is because when the volume decreases, the same number of particles collide with the walls of a container but more frequently as there is less space
However, the particles still collide with the same amount of force meaning greater force per unit area (pressure)
The key assumption is that the temperature and the mass (and number) of the particles remains the same