Kinetic Theory: Kinetic Energy – JSS2 Basic Science Lesson Note (Second Term)

Kinetic energy is the energy a body has because it is moving.

Behavioural objectives

1. Define kinetic energy.
2. State the ideas of Dalton’s atomic theory.
3. State the assumptions of the kinetic theory of matter.
4. Describe how the particles are arranged and move in a solid, a liquid and a gas.
5. Explain how an increase in heat affects the motion of particles and the state of matter.

What is kinetic energy?

Kinetic energy is the energy a body has by its motion.

• Moving bodies: a running footballer, a moving car and a falling mango all have kinetic energy.
• Bodies at rest: a body that is not moving has no kinetic energy of motion.
• Mass: a heavier body moving at the same speed has more kinetic energy.
• Speed: a faster body of the same mass has more kinetic energy.
• Unit: energy is measured in joules (J).

What is the kinetic theory of matter?

The kinetic theory of matter says that matter is made up of tiny particles that are always moving and therefore have kinetic energy.

There are three kinds of particles that make up matter: atoms, molecules and ions.

• Atoms: the smallest parts of an element, such as the atoms in iron or carbon.
• Molecules: two or more atoms joined together, as in water and oxygen.
• Ions: atoms or groups of atoms that carry an electric charge, as in common salt.

What is Dalton’s atomic theory?

Dalton’s atomic theory is a set of ideas, put forward by the British scientist John Dalton in the early 1800s, which says that matter is made of atoms.

His four ideas are:

1. Matter is made up of minute indivisible particles called atoms.
2. Atoms cannot be created or destroyed.
3. All the atoms of an element are alike and different from the atoms of all other elements.
4. Atoms combine in small whole numbers to form new substances.

• Effect of the theory: scientists have accepted that matter is made up of particles.
• Later knowledge: atoms are now known to contain smaller particles: protons, neutrons and electrons.

What are the assumptions of the kinetic theory?

The assumptions of the kinetic theory deal with the energy due to the movement of particles.

1. Matter is made up of tiny indivisible particles that are in constant motion and therefore possess kinetic energy.
2. An increase in heat supply or in temperature increases the motion of the particles and so increases their average kinetic energy.
3. An increase in the kinetic energy of the particles, due to more heat, brings about a change in state between solid, liquid and gas.

How do particles behave in solids, liquids and gases?

There are three states of matter: solid, liquid and gas.

• Solid: particles are packed closely and only vibrate in place, as in ice and iron.
• Liquid: particles are close but can slide past one another, as in water and palm oil.
• Gas: particles are far apart and move quickly in all directions, as in air and steam.

How does heat change the motion of particles?

Heat increases the kinetic energy of particles, so they move faster.

1. Heat energy is supplied to the substance, or its temperature rises.
2. The particles gain kinetic energy.
3. The particles vibrate or move faster.
4. The particles move further apart and the forces holding them weaken.
5. At a certain temperature the substance changes state.

What are the changes of state?

A change of state is the change of a substance from one state of matter to another when heat is gained or lost.

What is diffusion?

Diffusion is the spreading of particles from where they are many to where they are few, without stirring.

• Evidence: the smell of cooking soup spreads through a house because its particles move constantly.
• Effect of heat: diffusion is faster in warm surroundings because the particles move faster.

Evaluation

1. What is kinetic energy?
2. State the four ideas of Dalton’s atomic theory.
3. Name three kinds of particles that make up matter, according to the kinetic theory.
4. What happens to the motion of particles when the temperature increases?
5. Which state of matter has particles with the most kinetic energy?

Assignment

Write out the three assumptions of the kinetic theory of matter. Explain in your own words how an increase in heat supply can change the state of matter.