particles & matter

What is the particle model?

A model that describes matter as being made of tiny particles that are always moving. $

What are the three states of matter?

Solid, liquid and gas. $

How are particles arranged in a solid?

Closely packed in a regular arrangement. $

How do particles move in a solid?

They vibrate about fixed positions. $

How strong are the forces between particles in a solid?

Very strong. $

Why does a solid have a fixed shape?

The particles are held in fixed positions by strong forces. $

Why does a solid have a fixed volume?

The particles are packed closely together and cannot move apart easily. $

How are particles arranged in a liquid?

Close together but in a random arrangement. $

How do particles move in a liquid?

They move and slide past each other. $

How strong are the forces between particles in a liquid?

Strong enough to keep the particles close together but weak enough to let them move. $

Why does a liquid take the shape of its container?

Its particles can move past each other. $

Why does a liquid have a fixed volume?

The particles remain close together. $

How are particles arranged in a gas?

Far apart and randomly arranged. $

How do particles move in a gas?

Rapidly and freely in all directions. $

How strong are the forces between particles in a gas?

Very weak or negligible. $

Why does a gas fill its container?

The particles move freely in all directions. $

Why is a gas easily compressed?

There are large gaps between the particles. $

What happens to particles when a substance is heated?

They gain kinetic energy. $

What happens to the speed of particles when temperature increases?

They move faster. $

What is temperature a measure of?

The average kinetic energy of the particles. $

What happens to particles during melting?

They gain kinetic energy, overcome some of the attractive forces and begin to move past each other. $

What happens to the arrangement of particles during melting?

They change from a regular arrangement to a random arrangement. $

What happens to the forces between particles during melting?

Some of the attractive forces are overcome. $

Does the size of the particles change during melting?

No, only their arrangement and motion change. $

What happens to particles during freezing?

They lose kinetic energy and become fixed in position. $

What happens during evaporation?

The fastest-moving particles escape from the surface of a liquid. $

Why does evaporation cause cooling?

The highest-energy particles leave, reducing the average kinetic energy of the remaining particles. $

What is boiling?

Rapid vaporisation throughout the liquid at a fixed temperature. $

What is condensation?

A gas changing into a liquid as particles lose kinetic energy. $

What happens to the particles during condensation?

They slow down and move closer together. $

What is sublimation?

A solid changing directly into a gas without becoming a liquid. $

What is deposition?

A gas changing directly into a solid. $

What is density?

Mass per unit volume. $

State the equation for density.

Density = mass ÷ volume (ρ = m/V). $

What is the unit of density?

kg/m³ (or g/cm³). $

Why are solids usually more dense than gases?

Their particles are packed much closer together. $

What happens to the volume of most substances when heated?

It increases due to thermal expansion. $

Why do substances expand when heated?

Particles move more and become slightly further apart on average. $

How does heating affect the pressure of a gas in a sealed container?

The pressure increases. $

Why does heating a gas increase its pressure?

Faster particles collide with the container more often and with greater force. $

What is internal energy?

The total energy stored by the particles of a substance. $

What two energy stores make up internal energy?

Kinetic energy and potential energy. $

What happens to internal energy when a substance is heated?

It increases. $

What is specific heat capacity?

The energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K). $

State the equation for thermal energy transfer.

E = mcΔT $

What does E represent in E = mcΔT?

Energy transferred (J). $

What does m represent in E = mcΔT?

Mass (kg). $

What does c represent in E = mcΔT?

Specific heat capacity (J/kg°C or J/kgK). $

What does ΔT represent in E = mcΔT?

Temperature change (°C or K). $

What is latent heat?

Energy needed to change the state of a substance without changing its temperature. $

Why does temperature stay constant during a change of state?

The energy is used to overcome attractive forces between particles rather than increase kinetic energy. $

What is specific latent heat?

The energy required to change the state of 1 kg of a substance without changing its temperature. $

State the equation for latent heat.

E = mL $

What does L represent in E = mL?

Specific latent heat (J/kg). $

What is conduction?

The transfer of thermal energy through collisions between particles. $

Where does conduction mainly occur?

In solids. $

Why are metals good conductors of heat?

Delocalised electrons transfer energy rapidly through the metal. $

What is convection?

The transfer of thermal energy by the movement of fluids (liquids and gases). $

How does convection occur?

Warm fluid becomes less dense and rises while cooler, denser fluid sinks. $

What is a convection current?

The circular movement of a fluid caused by density differences. $

What is infrared radiation?

Electromagnetic radiation that transfers thermal energy. $

Can infrared radiation travel through a vacuum?

Yes. $

Do conduction and convection work in a vacuum?

No. $

What colour is the best absorber of infrared radiation?

Matt black. $

What colour is the best emitter of infrared radiation?

Matt black. $

What colour is the poorest absorber of infrared radiation?

Shiny silver. $

What colour is the poorest emitter of infrared radiation?

Shiny silver. $

How does insulation reduce heat transfer by conduction?

It traps air, which is a poor conductor. $

How does insulation reduce heat transfer by convection?

It prevents convection currents from forming. $

Why is air a good insulator?

It is a poor conductor of heat. $

Why are cavity walls used in houses?

They reduce heat loss by conduction and convection. $

Why is loft insulation effective?

It traps air and reduces heat transfer through the roof. $

Why is double glazing effective?

The trapped air or vacuum reduces conduction and convection. $