The kinetic theory of gases

Gases

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Homework

The kinetic theory of gases

Gases

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How the kinetic theory explains the gas laws.
Absolute zero, the lowest temperature possible.

1. Where does it come from?

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What is the kinetic theory and how did it emerge?

2. What does it say?

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Learn about the kinetic theory. What does it say about gases?

3. The kinetic theory and gas laws

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How does the kinetic theory explain the gas laws?

4. Absolute zero

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Do particles in a gas ever stop moving?

Learn what the lowest possible temperature is.

5. Check your progress

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See how much you have learnt before you go to class.

6. Solve the challenge

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In what everyday phenomena is the kinetic theory of gases evident?

The kinetic theory of gases

Gases

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1. How did the kinetic theory emerge?

The kinetic theory emerged in the 19th century as a result of the work of the scientists James C. Maxwell (1831-1879) and Ludwig E. Boltzmann (1844 -1906) to explain the behaviour of gases.

Look at the following images and think: what is different between a solid, a liquid and a gas?

The kinetic theory of gases

Gases

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2. What does kinetic theory say?

The kinetic theory assumes the following postulates:

Gases are made up of very small particles.

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The kinetic theory considers that gases are made up of very small particles. The volume of these particles is much smaller than the volume of the container. We can assume that each particle moves through the entire volume of the container.

There are no bonds.

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There are no binding forces between the particles of a gas. The particles move freely.

The particles of the gas move in a straight line.

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They only change direction when they collide with another particle or against the walls. After the collision, the particles move in another direction, but with the same speed.

The pressure exerted by the gas is a measure of the number of collisions.

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The higher the pressure, the greater the number of collisions per second of its particles against the walls of the container.

The absolute temperature of the gas is proportional to the velocity of the particles.

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The higher the velocity of the particles in a gas, the higher its temperature.

The kinetic theory of gases

Gases

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3. The kinetic theory and gas laws

The kinetic theory can be used to explain the experimental gas laws.

How the kinetic theory explains Boyle-Mariotte’s law

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$normal T espacio igual espacio constant normal p subíndice 1 espacio por espacio normal V subíndice 1 espacio igual espacio normal p subíndice 2 espacio por espacio normal V subíndice 2$

The temperature remains constant because the speed at which the gas particles move remains constant.

If the volume of the container is reduced, it takes the particles less time to hit the walls. Therefore, the number of collisions per second increases and we detect an increase in pressure.

If the volume of the container is increased, it takes the particles longer to hit the walls. Therefore, the number of collisions per second decreases and we detect a decrease in pressure.

How the kinetic theory explains Gay-Lussac’s law

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$V espacio igual espacio constant fracción p subíndice 1 entre T subíndice 1 espacio igual espacio fracción p subíndice 2 entre T subíndice 2$

When a gas is heated, its temperature increases because its particles move faster. If the volume of the container remains constant, the particles will take less time to hit the walls.

The number of collisions per second increases and we detect an increase in pressure.

When the gas is cooled, its temperature decreases because its particles move more slowly. If the volume of the container remains constant, the particles will take longer to hit the walls.

The number of collisions per second decreases and we detect a decrease in pressure.

How the kinetic theory explains Charles’ law

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$p espacio igual espacio c o n s t a n t fracción V subíndice 1 entre T subíndice 1 espacio igual espacio fracción V subíndice 2 entre T subíndice 2$

When the gas is heated, its temperature increases because its particles move faster.

For the pressure of the gas to remain constant, the volume of the container must be increased in order for the particles to hit the walls the same number of times per second.

When a gas is cooled, its particles move more slowly. For the number of collisions against the walls per second to remain the same, the volume of the container must be decreased.

The kinetic theory of gases

Gases

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4. Do particles ever stop moving? Absolute zero

According to kinetic theory, the temperature of a gas is higher when the particles move faster. If the particles move more slowly, the temperature decreases. There is a temperature at which particles stop moving. When that happens, temperature can't go any lower.

The temperature at which all movement of the particles stops is absolute zero. Nothing in the universe can be colder than absolute zero.

The kelvin temperature scale

The kelvin temperature scale starts at absolute zero, which is the temperature at which gas particles stop moving. It is the lowest possible temperature, and is equivalent to —273.15 ºC.

The kinetic theory of gases

Gases

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5. Check your progress

Consider the following sentences concerning the kinetic theory of gases and choose the correct answers.

The forces that bind particles in gases are .
Particles move in a line.
When particles collide with walls, their speed .
The of a gas is a measure of the number of collisions per second of its particles against the walls of the container.
The temperature of a gas is when its particles decrease in speed.

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The kinetic theory of gases

Gases

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Choose the correct answer in each case.

The kinetic theory of gases assumes that:
- The volume of the particles is much larger than the volume of the container.
- Gases are made up of very small particles that are separated from each other.
- A great part of the particles in a gas remains still inside the container.
- The particles of a gas move in curved lines until they find the walls of the container.
Correct answer

Wrong answer
The temperature below which the particles of a gas can not move is:
- -273.15 K
- 0 ºC
- 0 K
- -273.15 ºF
Correct answer

Wrong answer
Which scientists formulated the kinetic theory?
- Maxwell and Boltzmann.
- Gay-Lussac and Maxwell.
- Gay-Lussac and Alexandre Charles.
- Alexandre Charles and Robert Boyle.
Correct answer

Wrong answer
The absolute temperature of a gas is proportional to:
- The pressure.
- The forces of union between particles.
- The amount of gas in the container.
- The speed of the particles that form it.
Correct answer

Wrong answer

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The kinetic theory of gases

Gases

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Are these sentences true or false?

Absolute zero is the lowest temperature that could be reached with current technical means.

True

False
Correct answer

Wrong answer
At absolute zero, the velocity of particles is zero.

True

False
Correct answer

Wrong answer
At absolute zero, gases do not exert pressure.

True

False
Correct answer

Wrong answer

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The kinetic theory of gases

Gases

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Classwork

The kinetic theory of gases

Gases

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6. Solve the challenge

STEM
competences

STEM competences

Mathematical competence is the ability to develop and apply mathematical thinking and insight to solve problems in everyday situations.

Competence in science refers to the ability and willingness to explain the natural world by making use of scientific concepts, theories and methods, and to draw evidence-based conclusions.

Competences in technology and engineering are applications of mathematical and scientific knowledge to find solutions to human wants and needs.

These competences involve an understanding of the changes caused by human activity and responsibility as individual citizens.

Personal, social and learn to learn competence

Learn to learn competence

Personal, social and learning to learn competence is the ability to reflect to understand and accept oneself and promote continual personal growth, effectively manage time and information, work with others in a constructive way, remain resilient and manage one’s own learning and career.

It involves contributing to the physical, mental and emotional well-being of others and dealing with conflicts with empathy and support.

In groups, if possible, discuss with examples from everyday life how the kinetic theory of gases can be applied to explain their behaviour.

Write down the situations and the way you can explain them using the kinetic theory. For example: can you use it to explain how the smell of cooking food can fill the house?

(0 words)

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The kinetic theory of gases

Gases

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Now I know

The kinetic theory and gases

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The kinetic theory considers that gases are made up of very small particles with no binding forces.
These particles move freely inside the container, in a straight line. They only change direction when they collide with each other or with the walls of the container.
Pressure in a gas is a measure of the number of collisions of the particles against the walls of the container. More collisions means more pressure.
Temperature in a gas is proportional to the speed of the particles.

Absolute zero

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Temperature is a measure of the speed of the particles in the gas. The lower the temperature, the less speed particles will have.

When particles don't move, the gas is at absolute zero temperature. Temperature cannot decrease any further.

This lowest temperature is called absolute zero and is equivalent to –273.15 ºC.

Summary. The kinetic theory of gases

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Homework

Ready to learn?

1. How did the kinetic theory emerge?

Look at the following images and think: what is different between a solid, a liquid and a gas?

2. What does kinetic theory say?

3. The kinetic theory and gas laws

4. Do particles ever stop moving? Absolute zero

The kelvin temperature scale starts at absolute zero, which is the temperature at which gas particles stop moving. It is the lowest possible temperature, and is equivalent to —273.15 ºC.

5. Check your progress

Consider the following sentences concerning the kinetic theory of gases and choose the correct answers.

Choose the correct answer in each case.

Are these sentences true or false?

Classwork

6. Solve the challenge

In groups, if possible, discuss with examples from everyday life how the kinetic theory of gases can be applied to explain their behaviour.

Now I know