# States of matter

?

## Matter and particles

The particles of a solid are held together in fixed positions and they are the least energetic of the states of matter

The particles of a liquid move about at random and they are in contact with each other.

The particles of a gas move around randomly and they are far apart. They are the most energetic of the states of the matter.

During a physical change of state no new substances are made.

The particle model has two limitations:

There are no forces shown

Atoms are elastic not inelastic as shown in the model.

1 of 8

## Density

Density= Mass/Volume in kg/m3

To measure density of a solid object or liquid; measure its mass and volume then use the equation.

Objects that are less dense than water <1000 kg/m3 float in water.

Gases are much less dense than solid or liquids.

2 of 8

## Gas pressure and temperature

The pressure of a gas is caused by the random impacts of gas molecules on surfaces that are in contact with the gas.

If the temperature of a gas in a sealed space increases the pressure of the gas increases because:

the molecules move faster, therefore they collide with more force

the number of impacts per second on the container increase

the total force of the impacts increases

The unpredictable motion of smoke particles is evidence of the random motion of gas molecules.

The random motion of tiny particles in a fluid is called Brownian Motion. Pollen grains on water, Brownian motion puzzled everyone until kinetic theory of matter provided an explanation.

3 of 8

## Changes of state

For a pure substance:

Its melting point is the temperature at which it melts

Its boiling point is the temperature at which it boils

Energy is needed to melt a solid or boil a liquid.

When a substance changes state its mass stays the same.

The flat section of a temperature vs time graph gives the melting point or the boiling point of a substance.

4 of 8

## Internal Energy

Increasing the internal temperature of a substance inreases its internal energy.

The strength of forces between the particles of a substance explains its state of matter at room temperature.

When a substance is heated:

if its temperature increases the kinetic engergy of its particles increases

if it melts or boils the potential energy of the particles increases

The pressure of a gas on a surface is caused by the particles of the gas repeatedly hitting the surface.

5 of 8

## Specific heat capacity

The specific heat capacity of a substance is the enrgy needed to raise the temperature of 1 kg of the substance by 1 degree celcius.

Energy transferred (J) = Mass (M) x Specific Heat Capacity (J/kg c) x Temperature change (C)

The greater the mass of an object , the more slowly its temperature increases when it is heated

Storage heaters- energy transfers from bricks to keep the room warm, they have a high specific heat capacity so they store a lot of energy. They warm up slowly when the heater is on and they cool down slowly when is it off.

6 of 8

## Specific latent heat

Specific latent heat of fusion (L) (J/kg) = Energy (E) (J)/Mass (m) (kg)

Latent heat is the energy needed for a substance to change its state without changing its temperature.

Specific latent heat of fusion is the energy needed to melt or boil 1kg of a substance without changing its temperature.

The specific latent heat of fusion of ice can be measured using a low-voltage heater to melt the ice.

7 of 8

## Pure substances and mixtures

Pure substances can be compounds or elements, but they contain only one substance.

An impure substance is a mixture of two or more different elements or compounds.

Pure elements and compunds melt and boil at specific temperatures, and these melting and boiling points can be used to identify them.

Melting point and boiling point data can be used to distinguish pure substances from mixtures.

8 of 8