9. Temperature and Ideal Gases Flashcards
Define thermal equilibrium.
Thermal equilibrium occurs when there is no net exchange of energy when two objects are placed in thermal contact.
What happens to the temperature of a cup of hot coffee when it has been placed on a table for a very long time?
The temperature of the coffee will be the same as its surroundings.
In what situation will there be no net transfer of thermal energy between two objects?
When there is no heat flow between the two objects as they are both at the same temperature in thermal equilibrium.
Using the kinetic theory of gases, explain how a gas exerts a pressure on the walls of a container.
Step 3:
- The gas is made up of a large number of particles in constant, random motion, which possess momentum
- When they collide with the walls of the container, they experience a change of momentum
- By Newton’s 2nd Law, a force exerted by the wall will act on the particles to cause a change in momentum of the particles
- By Newton’s 3rd Law, the particles will exert a force (thus a pressure) on the wall of the container
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on the nature of their movement.
They are in constant random motion and obey Newton’s Law of Motion.
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on their volume.
The volume of each particle is negligible compared to the volume of the gas.
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on the intermolecular forces of attraction between the molecules.
Intermolecular forces between the particles are negligible except during the time of collision.
(Having negligible forces between particles implies that the microscopic potential energy of the particles is constant at 0J.)
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on the number of particles present.
Any gas is made up of a large number of particles.
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on duration of collisions.
The duration of collisions is negligible compared to the time interval between collisions.
The kinetic theory of gases is based on some simplifying assumptions. The molecules of the gas are assumed to behave as hard elastic identical spheres.
State the basic assumption about the molecules of an ideal gas based on the conservation of energy when molecules hit each another/the wall.
The particles make perfectly elastic collisions among themselves and the wall of the container.
A cube of volume V contains N molecules of an ideal gas. Each molecule has a
component cx of velocity normal to one side S of the cube.
The pressure p of the gas due to component cx of velocity is given by the expression, pV = Nm < (cx)^2 >
Where m is the mass of a molecule.
Explain how the expression leads to the relation, p = ( 1/3 ) x density (p) < c^2 >
where < c^2 > is the mean speed of the molecules.
Since < c^2> = < (cx)^2 > + < (cy)^2 > + < (cz)^2 >
The velocity of the molecules has 3 components. Due to the random motion and the large number of particles,
< (cx)^2 > = < (cy)^2 > = < (cz)^2 > = ( 1/3 ) < c^2 >
and therefore, pV = ( 1/3 ) Nm Note: density = m / V
p = ( 1/3 ) x density (p) (shown)
