5.1.4 Ideal Gases

Question 1

What are the assumptions in the kinetic model for an ideal gas?

Answer 1

• There are a large number of gas particles in random, rapid motion.
• Particles occupy negligible volume compared to the volume of the gas.
• All collisions are perfectly elastic.
• The time of collision between the particles is negligible compared to the time between collisions.
• Electrostatic forces between particles are negligible, except during collisions.

Question 2

Explain pressure in terms of the kinetic theory of gases and Newton’s laws of motion.

Answer 2

• Particles of a gas are always moving, and collide with the walls of the container.
• When the particles collide with the walls of the container the wall exerts a force on the particle, F=Δp/Δt.
• The particles also exert equal and opposite force on the walls.
• A large number of particles collide randomly with the walls of the container, exerting a total force F on the area A of the walls.
• P=F/A

Question 3

What is Boyle’s law?

Answer 3

• P is inversely proportional to V
• PV = constant

Question 4

What is the relationship between pressure and temperature?

Answer 4

• P is directly proportional to T
• P/T = constant

Question 5

What is the equation of state of an ideal gas?

Answer 5

PV=nRT

Question 6

How can you estimate absolute zero using a P-T graph?

Answer 6

• The temperature at which the graph crosses the x-axis is absolute 0.
• This is because at absolute 0, particles do not move, so they cannot collide with the container, and have no pressure.

Question 7

What is the r.m.s speed of particles in a gas?

Answer 7

• Square the velocity of each particle.
• Find the average of these squared velocities.
• Take the square root of this mean.

Question 8

What equation links pV to the r.m.s speed?

Answer 8

pV=Nmc

• Where N = number of particles
• c = r.m.s speed

Question 9

What is the Boltzmann constant?

Answer 9

k=R/Na

R = molar gas constant
Na = Avogardo’s constant