State three assumptions of the kinetic theory of gases relating to the properties of the gas molecules themselves.

Any three from: Molecules are identical (or all have the same mass) Molecules are hard, perfectly elastic spheres The volume of the molecules is negligible compared to the volume of the container There are no forces of attraction or repulsion between the molecules There is a very large number of molecules

State three assumptions of the kinetic theory of gases relating to the motion and collisions of gas molecules.

Any three from: Molecules are in continuous random motion External forces (e.g. gravity) are ignored Newton's laws apply to the molecules Molecules collide perfectly elastically with the container walls, exerting a pressure The time of a collision is negligible compared to the time between collisions

One assumption of the kinetic theory of gases is that the .......... of the gas molecules is negligible compared to the volume of the container.

One assumption of the kinetic theory of gases is that the volume of the gas molecules is negligible compared to the volume of the container.

True or False? Gas molecules lose kinetic energy when they collide with the walls of their container.

False. Collisions with the container walls are perfectly elastic , so no kinetic energy is lost.

The pressure exerted by a gas on the walls of its container arises from the .......... in momentum of molecules colliding with the walls.

The pressure exerted by a gas on the walls of its container arises from the change in momentum of molecules colliding with the walls.

True or False? The root-mean-square speed of gas molecules is the same as their mean (average) speed.

False. The mean velocity of all molecules averages to zero , since velocity is a vector and directions cancel. The r.m.s speed is found by squaring speeds first (removing sign), averaging, then square-rooting, so the two are not equal .

Define translational kinetic energy for a gas.

Translational kinetic energy is the kinetic energy of the molecules as determined by their temperature .

The average kinetic energy of a gas molecule is directly proportional to its .......... temperature.

The average kinetic energy of a gas molecule is directly proportional to its thermodynamic temperature.

A LevelPhysicsCambridge (CIE)Flashcards15. Ideal GasesKinetic Theory of Gases

Kinetic Theory of Gases (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontKinetic Theory of Gases
State three assumptions of the kinetic theory of gases relating to the properties of the gas molecules themselves.
BackKinetic Theory of Gases
Any three from:
Molecules are identical (or all have the same mass)
Molecules are hard, perfectly elastic spheres
The volume of the molecules is negligible compared to the volume of the container
There are no forces of attraction or repulsion between the molecules
There is a very large number of molecules
BackKinetic Theory of Gases
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FrontKinetic Theory of Gases
State three assumptions of the kinetic theory of gases relating to the motion and collisions of gas molecules.
BackKinetic Theory of Gases
Any three from:
Molecules are in continuous random motion
External forces (e.g. gravity) are ignored
Newton's laws apply to the molecules
Molecules collide perfectly elastically with the container walls, exerting a pressure
The time of a collision is negligible compared to the time between collisions

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Cards in this collection (17)

State three assumptions of the kinetic theory of gases relating to the properties of the gas molecules themselves.
Any three from:
- Molecules are identical (or all have the same mass)
- Molecules are hard, perfectly elastic spheres
- The volume of the molecules is negligible compared to the volume of the container
- There are no forces of attraction or repulsion between the molecules
- There is a very large number of molecules
State three assumptions of the kinetic theory of gases relating to the motion and collisions of gas molecules.
Any three from:
- Molecules are in continuous random motion
- External forces (e.g. gravity) are ignored
- Newton's laws apply to the molecules
- Molecules collide perfectly elastically with the container walls, exerting a pressure
- The time of a collision is negligible compared to the time between collisions
One assumption of the kinetic theory of gases is that the .......... of the gas molecules is negligible compared to the volume of the container.
One assumption of the kinetic theory of gases is that the volume of the gas molecules is negligible compared to the volume of the container.
True or False?
Gas molecules lose kinetic energy when they collide with the walls of their container.
False.
Collisions with the container walls are perfectly elastic, so no kinetic energy is lost.
State the kinetic theory of gases equation relating pressure and volume to the mean square speed of the molecules.
$p V = \frac{1}{3} N m \left < c^{2} \right >$
State the kinetic theory of gases equation for pressure in terms of the density ρ of the gas.
$p = \frac{1}{3} ρ \left < c^{2} \right >$
Define root-mean-square speed.
The root-mean-square speed ( $c_{r . m . s}$ ) is the square root of the mean square speed of the gas molecules: $c_{r.m.s} = \sqrt{\left}$
In the derivation of the kinetic theory equation, why is only one-third of the mean square speed used to find the pressure on one wall of the container?
Molecules move randomly in 3D, and the mean square speed is equally distributed between the x, y and z directions, so $\left < c_{x}^{2} \right > = \frac{1}{3} \left < c^{2} \right >$ . Only the component of velocity perpendicular to a wall contributes to the pressure on it.
In the kinetic theory model, what is the change in momentum of a molecule that rebounds elastically from a container wall with speed c?
$Δ p = - 2 m c$
(the molecule reverses direction with the same speed, since the collision is perfectly elastic)
The pressure exerted by a gas on the walls of its container arises from the .......... in momentum of molecules colliding with the walls.
The pressure exerted by a gas on the walls of its container arises from the change in momentum of molecules colliding with the walls.
True or False?
The root-mean-square speed of gas molecules is the same as their mean (average) speed.
False.
The mean velocity of all molecules averages to zero, since velocity is a vector and directions cancel. The r.m.s speed is found by squaring speeds first (removing sign), averaging, then square-rooting, so the two are not equal.
State the equation for the average translational kinetic energy of one molecule of an ideal gas.
$E_{k} = \frac{1}{2} m \left < c^{2} \right > = \frac{3}{2} k T$
State the equation for the total average translational kinetic energy of all N molecules in an ideal gas.
$E_{k - t o t a l} = \frac{3}{2} N k T$
Define translational kinetic energy for a gas.
Translational kinetic energy is the kinetic energy of the molecules as determined by their temperature.
For an ideal gas, how does the root-mean-square speed of the molecules relate to the thermodynamic temperature?
$c_{r . m . s} \propto \sqrt{T}$
since <c²> is directly proportional to T (as mass m and the Boltzmann constant k are constant)
The average kinetic energy of a gas molecule is directly proportional to its .......... temperature.
The average kinetic energy of a gas molecule is directly proportional to its thermodynamic temperature.
True or False?
Doubling the thermodynamic temperature of an ideal gas doubles the root-mean-square speed of its molecules.
False.
Since $c_{r . m . s} \propto \sqrt{T}$ , doubling T increases $c_{r . m . s}$ by a factor of $\sqrt{2}$ , not 2.

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