The gas laws are empirical, based on observation and evidence of how a gas responds to changes in volume, pressure and temperature.

Define kinetic theory (of gases).

Kinetic theory is based on assumptions and derivations from existing theories, used to explain why the gas laws behave the way they do.

Name the relationships classed as the gas laws .

Boyle's Law Charles's Law Pressure Law The ideal gas equation

Why do the molecules of an ideal gas have no potential energy?

Ideal gas molecules are assumed to have no intermolecular forces , so they have no potential energy, only kinetic energy .

The internal energy of an ideal gas is the sum of all the .......... of the particles.

The internal energy of an ideal gas is the sum of all the kinetic energies of the particles.

True or False? For an ideal gas, internal energy is directly proportional to volume.

False. For an ideal gas, internal energy is directly proportional to temperature , since temperature is proportional to average kinetic energy.

State four assumptions made by the kinetic theory of gases model.

Molecules behave as identical , with the same mass Molecules are hard, perfectly elastic spheres The volume of the molecules is negligible compared to the volume of the container The time of a collision is negligible compared to the time between collisions There are no intermolecular forces between molecules, except during impact External forces, such as gravity, are ignored Molecules move in continuous random motion Newton's laws apply There are a very large number of molecules

In the kinetic theory model, the volume of the molecules themselves is .......... compared to the volume of the container.

In the kinetic theory model, the volume of the molecules themselves is negligible compared to the volume of the container.

True or False? The kinetic theory of gases model assumes that collisions between molecules and the container walls are inelastic.

False. The model assumes molecules are hard, perfectly elastic spheres, so no kinetic energy is lost in collisions.

The mean kinetic energy of an ideal gas molecule is .......... to its thermodynamic temperature.

The mean kinetic energy of an ideal gas molecule is proportional to its thermodynamic temperature.

True or False? The equation E k = (3/2) kT gives the total kinetic energy of all the molecules in an ideal gas.

False. This equation gives the average kinetic energy of a single molecule. To find the total kinetic energy of all molecules, multiply by N .

Define Brownian motion .

Brownian motion is the phenomenon in which small particles suspended in a liquid or gas, such as pollen or smoke particles, are observed to move around in a random, erratic fashion.

What does Brownian motion provide evidence for?

Brownian motion provides evidence for the existence of atoms in a gas or liquid.

How can Brownian motion be observed?

Brownian motion can be observed under a microscope .

In random motion, particles have a .......... of speeds and no preferred direction of movement.

In random motion, particles have a range of speeds and no preferred direction of movement.

In Brownian motion, how does the size of the observable particles (e.g. smoke) compare with the molecules causing their motion (e.g. air)?

The observable particles are significantly bigger and heavier than the molecules that cause the motion, which are small and light.

Why are the small, fast-moving molecules able to change the speed and direction of the much larger observable particles when they collide?

The small molecules travel at a much higher speed than the larger particles and have a lot of momentum , which they transfer to the larger particles when they collide.

True or False? The random, erratic movement seen in Brownian motion happens because the visible particles are moving under their own energy.

False. It happens because the visible particles are being bombarded by fast-moving, invisible gas or liquid molecules colliding with them from random directions.

Define atomos (Democritus).

Atomos , meaning 'indivisible', was Democritus's name for the infinitesimally small pieces of matter left after continually cutting an object into smaller and smaller pieces. This is the etymology of the word 'atom'.

Who discovered the relationship between the pressure and volume of a gas at constant temperature, and what is this relationship called?

Robert Boyle (1662) discovered this relationship, known as Boyle's Law .

Who discovered the relationship between the volume and temperature of a gas at constant pressure, and what is this relationship called?

Jacques Charles (1787) discovered this relationship, known as Charles's Law .

Who discovered the relationship between the temperature and pressure of a gas at constant volume, and what is this relationship called?

Guillaume Amontons (1699), and later also Joseph Louis Gay-Lussac (1809), discovered this relationship, known as the Pressure Law .

What discovery did Robert Brown make in 1827, and why was it significant?

Brown discovered Brownian motion , the random motion of particles in a fluid. This gave evidence that a fluid is made up of tiny atoms or molecules moving very quickly and randomly, supporting kinetic theory .

What did Einstein's 1905 paper on Brownian motion achieve?

It used kinetic theory to make predictions for Brownian motion. Only after this did the atomic and kinetic theory of particles start to become widely accepted.

For a scientific theory to be accepted, other scientists must .......... experiments and obtain the same conclusions.

For a scientific theory to be accepted, other scientists must repeat experiments and obtain the same conclusions.

True or False? Democritus's ideas about atoms were widely accepted by other Greek and Roman philosophers of his time.

False. Aristotle and Plato rejected his theories, and due to their influence, Democritus's ideas were not accepted until almost 2000 years later.

A LevelPhysicsAQAFlashcardsFurther Mechanics & Thermal PhysicsMolecular Kinetic Theory Model

Molecular Kinetic Theory Model (AQA A Level Physics): Flashcards

Exam code: 7408

1/36

0Still learning

Know0

FrontGas Laws v Kinetic Theory
Define gas laws.
FrontGas Laws v Kinetic Theory
Name the relationships classed as the gas laws.
BackGas Laws v Kinetic Theory
Boyle's Law
Charles's Law
Pressure Law
The ideal gas equation

Was this flashcard helpful?

Cards in this collection (36)

Define gas laws.
The gas laws are empirical, based on observation and evidence of how a gas responds to changes in volume, pressure and temperature.
Define kinetic theory (of gases).
Kinetic theory is based on assumptions and derivations from existing theories, used to explain why the gas laws behave the way they do.
Name the relationships classed as the gas laws.
- Boyle's Law
- Charles's Law
- Pressure Law
- The ideal gas equation
Why do the molecules of an ideal gas have no potential energy?
Ideal gas molecules are assumed to have no intermolecular forces, so they have no potential energy, only kinetic energy.
The internal energy of an ideal gas is the sum of all the .......... of the particles.
The internal energy of an ideal gas is the sum of all the kinetic energies of the particles.
State the equation linking the internal energy, U, of an ideal gas to the number of particles, N, and the average kinetic energy of a single particle, E_k.
$U = N \times E_{k}$
True or False?
For an ideal gas, internal energy is directly proportional to volume.
False.
For an ideal gas, internal energy is directly proportional to temperature, since temperature is proportional to average kinetic energy.
Define root-mean-square speed, c_rms.
The root-mean-square speed is the square root of the average of the squared speeds of all the molecules in a gas:
$c_{r m s} = \sqrt{\frac{c_{1}^{2} + c_{2}^{2} + . . . + c_{N}^{2}}{N}}$
State four assumptions made by the kinetic theory of gases model.
- Molecules behave as identical, with the same mass
- Molecules are hard, perfectly elastic spheres
- The volume of the molecules is negligible compared to the volume of the container
- The time of a collision is negligible compared to the time between collisions
- There are no intermolecular forces between molecules, except during impact
- External forces, such as gravity, are ignored
- Molecules move in continuous random motion
- Newton's laws apply
- There are a very large number of molecules
In the kinetic theory model, the volume of the molecules themselves is .......... compared to the volume of the container.
In the kinetic theory model, the volume of the molecules themselves is negligible compared to the volume of the container.
A molecule moving with velocity c₁ collides elastically and perpendicularly with a wall. What is its change in momentum?
$Δ p = - 2 m c_{1}$
The molecule rebounds with velocity $- c_{1}$ , since the collision is perfectly elastic.
True or False?
The kinetic theory of gases model assumes that collisions between molecules and the container walls are inelastic.
False.
The model assumes molecules are hard, perfectly elastic spheres, so no kinetic energy is lost in collisions.
State the kinetic theory of gases equation in terms of the number of molecules, N, and the mass of one molecule, m.
$p V = \frac{1}{3} N m (c_{r m s})^{2}$
State the kinetic theory of gases equation in terms of the density, $ρ$ , of the gas.
$p = \frac{1}{3} ρ (c_{r m s})^{2}$
Define the Boltzmann constant, k.
The Boltzmann constant relates the temperature of a gas to the average kinetic energy of its molecules:
$k = \frac{R}{N_{A}}$
where R is the molar gas constant and N_A is the Avogadro constant.
State the equation for the average kinetic energy, E_k, of one molecule of an ideal gas, in terms of the Boltzmann constant, k, and temperature, T.
$E_{k} = \frac{3}{2} k T$
The mean kinetic energy of an ideal gas molecule is .......... to its thermodynamic temperature.
The mean kinetic energy of an ideal gas molecule is proportional to its thermodynamic temperature.
State the equation for the internal energy, U, of an ideal gas of N particles, in terms of the Boltzmann constant, k, and temperature, T.
$U = \frac{3}{2} N k T$
What is the relationship between the internal energy, U, and the temperature, T, of an ideal gas?
Internal energy and temperature are directly proportional:
$U \propto T$
The average molecular kinetic energy equation, $E_{k} = \frac{3}{2} k T$ , is derived by equating which two equations?
- The ideal gas equation, $p V = N k T$
- The kinetic theory of gases equation, $p V = \frac{1}{3} N m (c_{r m s})^{2}$
True or False?
The equation E_k = (3/2)kT gives the total kinetic energy of all the molecules in an ideal gas.
False.
This equation gives the average kinetic energy of a single molecule. To find the total kinetic energy of all molecules, multiply by N.
Define Brownian motion.
Brownian motion is the phenomenon in which small particles suspended in a liquid or gas, such as pollen or smoke particles, are observed to move around in a random, erratic fashion.
What does Brownian motion provide evidence for?
Brownian motion provides evidence for the existence of atoms in a gas or liquid.
How can Brownian motion be observed?
Brownian motion can be observed under a microscope.
In random motion, particles have a .......... of speeds and no preferred direction of movement.
In random motion, particles have a range of speeds and no preferred direction of movement.
In Brownian motion, how does the size of the observable particles (e.g. smoke) compare with the molecules causing their motion (e.g. air)?
The observable particles are significantly bigger and heavier than the molecules that cause the motion, which are small and light.
Why are the small, fast-moving molecules able to change the speed and direction of the much larger observable particles when they collide?
The small molecules travel at a much higher speed than the larger particles and have a lot of momentum, which they transfer to the larger particles when they collide.
True or False?
The random, erratic movement seen in Brownian motion happens because the visible particles are moving under their own energy.
False.
It happens because the visible particles are being bombarded by fast-moving, invisible gas or liquid molecules colliding with them from random directions.
Define atomos (Democritus).
Atomos, meaning 'indivisible', was Democritus's name for the infinitesimally small pieces of matter left after continually cutting an object into smaller and smaller pieces. This is the etymology of the word 'atom'.
Who discovered the relationship between the pressure and volume of a gas at constant temperature, and what is this relationship called?
Robert Boyle (1662) discovered this relationship, known as Boyle's Law.
Who discovered the relationship between the volume and temperature of a gas at constant pressure, and what is this relationship called?
Jacques Charles (1787) discovered this relationship, known as Charles's Law.
Who discovered the relationship between the temperature and pressure of a gas at constant volume, and what is this relationship called?
Guillaume Amontons (1699), and later also Joseph Louis Gay-Lussac (1809), discovered this relationship, known as the Pressure Law.
What discovery did Robert Brown make in 1827, and why was it significant?
Brown discovered Brownian motion, the random motion of particles in a fluid. This gave evidence that a fluid is made up of tiny atoms or molecules moving very quickly and randomly, supporting kinetic theory.
What did Einstein's 1905 paper on Brownian motion achieve?
It used kinetic theory to make predictions for Brownian motion. Only after this did the atomic and kinetic theory of particles start to become widely accepted.
For a scientific theory to be accepted, other scientists must .......... experiments and obtain the same conclusions.
For a scientific theory to be accepted, other scientists must repeat experiments and obtain the same conclusions.
True or False?
Democritus's ideas about atoms were widely accepted by other Greek and Roman philosophers of his time.
False.
Aristotle and Plato rejected his theories, and due to their influence, Democritus's ideas were not accepted until almost 2000 years later.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Ideal GasesNext:Gravitational Fields