Partical model of Matter

Solids - stong forces of attraction hold the paricals in a fixed, regular arrangement. They dont have much energy so can only move in a fixed position.

Liquids - weaker forces of attraction between the particles which are close together but can move past each other to form irreguar arrangements. They can move in random directions at lower speeds.

Gases - almost no forces of attraction between the particles and are free to move in random directions at high speeds.

When particles in a gas collide with each other, or anything else, they exert a force. Pressure is the force they exert per unit area. So, in a sealed container, the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls.

Transfering energy to a gas will transfer energy to the kinetic energy stores of the particles. The temperature of a gas is related to the average energy in the kinetic energy stores. This means that increasing the temperature increases pressure. As each particle gains speed they hit the sides of the container more often and with a larger momentum.

Density is a measure of the "compactness" of a substance to how much space it takes up. A dense material has its particlas packed closely together whilst particles in a less density are more spaced out. Comprssing a material would move its particles closer together, without changing its mass. This means that solids are generally denser than liquids and gasses.

Density = mass / volume (kg/m^3 = kg / m^3)

To find the density of a solid object.

• Use a balance to measure its mass
• Measure the volume. If it is a regular solid, use a ruler, if it is an irregular shape submerge it in a eureka can filled with water. The water displaced by the object will be transferred to the measuring cylinder. Record the volume of water displaced and calculate the density.

To find the density of a liquid.

• Place a measuring cylinder on a balance and zero the balance.
• Pour 10ml of the liquid into ameasuring cylinder and record the liquid's mass and another 10ml into the measuring cylinder, repeating the process until the cylinder is full and recoreding the total volume and mass each time.
• Use the formula to find the density and find an average of your calculated densities.

The particles in a system vibrate and move around as they have energy in their kinetic energy stores. They also have potentail energy due to their positions, which is stored in the particles. The internal energy of a system is the total energy the particles have in both of these stores.

Heating the system transfers energy to the kinetic energy stores, increasing internal energy and causing a change in temperature or state.

A temperature schange is dependent upon: the mass of the sustance, what its made of (its specific heat capacity) and the energy input.

A change of state occurs if the substance is heated enough to break the bonds holding the particles together. A change of state is a physical change and can be returned to its original form with the same properties. The number of particles do not change and so mass is conserved.

When a substance is melting or boiling, the internal energy increases but it is used to break intermolecular bonds rather than raise the temperature. This is why there are flat spots on a heating graph, where energy is not being used to change the temperature.

When a substance is condensing or freezing, bonds are forming between particles, which releases energy. This means the internal energy decreases but the temperature does not go down until it has changed state.

The specific latent heat of an object is the amount of energy needed to change 1kg of the substance from one state to another without changing its temperature. For cooling, it is the energy release by a change of state.

• The specific latent heat for changing between a solid and a liquid is called the specific latent heat of fusion.
• For changing between a liquid and a gas it is called the specific latent heat of vaporisiation.

Energy (J) = Mass (kg) x Specific Latent Heat (J/kg)