07 Kinetic Particle Model of Matter

Why do solids have a fixed shape?

Particles of a solid are held together by very strong forces of attraction and vibrate about their fixed postions.

Explain why liquids do not have a fixed shape.

Particles of a liquid are held together by strong forces of attraction and can slide past one another within the liquid.

Explain why gases do not have a fixed shape.

The forces of attraction between gas particles is very weak. The particles can move quickly, randomly and continuously in all directions.

Explain why solids are denser than gases.

Particles of a solid are more closely packed than those in a gas.

What happens when particles in a gas are heated up.

The particles still move randomly but move faster and change direction more frequently.

What happens when particles in a gas cool down.

The particles still move randomly, but are slower on average and change directions less frequently.

Why do particles move faster when they are heated?

Why do the smoke particles also move faster?

The average kinetic energy of the particles increase as temperature increases.

They collide with the smoke particles with a larger average force per collision and more frequently.

Why can solids/liquids not be compressed?

The solid/liquid particles are already closely packed together and cannot move any more closer to one another.

Why can gases be compressed?

The gas particles are very far apart from each other and the attractive forces between the particles are weak.

Describe a Brownian Motion experiment

Smoke is trapped in a glass container. The smoke particles are observed to move in a haphazard manner.

How do particles in a gas create pressure?

Gas particles move about randomly, continuously in all directions. They collide with the inner walls of the syringe and exert a force on them. The average force per unit area is the gas pressure.

Explain how air molecules can create a large pressure.

The small individual forces of particles colliding with the inner walls of the container add up so that a large number of collidions results in a large total average force in the inner walls of the container. As pressure is force per unit area, this results in a large pressure.

What affects the pressure of gases

The frequency of collisions of the gas particles per unit area and average force per collision of gas particles on the inner walls of the container.