What causes gas pressure?

Gas particles colliding with the walls of the container.

Why does heating a gas in a sealed container increase pressure?

The particles move faster, so they hit the walls more often and with more force.

What happens to pressure if the volume of a gas is reduced at constant temperature?

It increases, because the particles collide with the walls more often.

What happens to pressure if more gas particles are added to a container?

It increases, because there are more collisions with the walls each second.

What is absolute zero?

The lowest possible temperature, 0 K or -273 °C.

The net movement of particles from higher to lower concentration, due to random motion.

Why is diffusion faster in gases than liquids?

Gas particles are further apart, weakly attracted and collide less often.

Why does diffusion speed up when temperature rises?

The particles have more kinetic energy and move faster.

What is Brownian motion?

Random, jerky movement of visible particles caused by collisions with fast, invisible particles.

Why is Brownian motion evidence for particles?

It shows that tiny particles in a gas or liquid move constantly and randomly and collide with larger ones.

Kinetic theory and gas behaviourIB MYP Sciences: Flashcards

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What does the kinetic theory say about particles?

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What does the kinetic theory say about particles?: They are in constant motion; their energy depends on temperature.
What causes gas pressure?: Gas particles colliding with the walls of the container.
Why does heating a gas in a sealed container increase pressure?: The particles move faster, so they hit the walls more often and with more force.
What happens to pressure if the volume of a gas is reduced at constant temperature?: It increases, because the particles collide with the walls more often.
What happens to pressure if more gas particles are added to a container?: It increases, because there are more collisions with the walls each second.
What is absolute zero?: The lowest possible temperature, 0 K or -273 °C.
How do you convert °C to K?: Add 273.
Convert 100 °C to kelvin.: 373 K.
What is diffusion?: The net movement of particles from higher to lower concentration, due to random motion.
Why is diffusion faster in gases than liquids?: Gas particles are further apart, weakly attracted and collide less often.
Why does diffusion speed up when temperature rises?: The particles have more kinetic energy and move faster.
What is Brownian motion?: Random, jerky movement of visible particles caused by collisions with fast, invisible particles.
Why is Brownian motion evidence for particles?: It shows that tiny particles in a gas or liquid move constantly and randomly and collide with larger ones.

Exam questions on Kinetic theory and gas behaviour

A hospital stores oxygen gas in sealed steel cylinders in a room with an air-conditioning system. The gas particles inside each cylinder are in constant random motion.
A cylinder is left in hot sunlight. Explain, in terms of particles, why the pressure of the gas inside it increases.2 marks
In a kitchen in Mumbai, the smell of spices frying on the stove reaches the far side of the room within a minute. In the same kitchen, a drop of food colouring added to a glass of water slowly spreads until the whole glass is coloured, without anyone stirring it.
The cook finds that the smell of the spices spreads more quickly when the kitchen is warm. Explain this using the particle model.2 marks
A class investigates how temperature affects diffusion. They add one crystal of potassium manganate(VII) to a beaker containing 200 cm³ of water and time how long it takes for the purple colour to spread evenly through the water. They repeat the test with water at different temperatures.
State a testable hypothesis for this investigation, including a scientific reason.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).