In solids, there are strong forces of attraction that hold particles in a fixed, regular arrangement. The particles vibrate about these fixed positions
In liquids, the forces of attraction between particles are weaker so particles are close together but can move past each other to form irregular arrangements. They move in random directions at low speeds.
In gases, there are no forces of attraction. Particles travel in random directions at high speeds
where ρ = Density (kg/m3), m = Mass (kg) and V = Volume (m3)
Generally, substances are most dense as solids and least dense as gases as volume increases as the space between molecules does due to weak forces of attraction. Mass is conserved as a substance in a closed system has the same number of particles. Changes in state are physical as no new substances are formed. The original properties can be recovered if the change is reversed
CORE PRACTICAL: Investigating Densities
A – To find the density of a liquid, use a measuring cylinder to find the volume of a certain amount of the substance
B – Measure the mass on a mass balance. Carry out the density calculation
C – To find the density of a solid, find its mass on a mass balance
D – If the solid is regular in shape, find volume by base × length × height
E – If the solid is irregularly shaped, fill a displacement can with a measuring cylinder placed ujder the spout
F – Drop in the object carefully. Let it sink, but if it floats gently push down until submerged. Find the volume displaced, which is equal to the volume of the solid. Carry out the density calculation
Heat
Heating a system will change the energy stored within the system and raise its temperature or produce a change of state. The Specific Heat Capacity (SHC) of a substance is the amount of energy needed to raise the temperature of 1kg of that substance by 1°C.
Use the equation where Q = Change in Thermal Energy (J), m = Mass (kg), c = SHC (J/kg°C) and Δθ = Change in Temperature (°C)
Specific Latent Heat of a change of state of a substance is the amount of energy needed to change 1kg of it from one state to another without changing the temperature. Between solid and liquid states the SLH is of fusion and between liquid and gas it is the SLH of vapourisation
Use the equation where Q = Change in Thermal Energy (J), m = Mass (kg) and L = Specific Latent Heat (J/kg)
To reduce heat loss, surround the object with insulating materials such as cotton, wool or foam
CORE PRACTICAL: Investigating Water
Part 1
A – To find the specific heat capacity of water, put a polystyrene cup in a beaker onto a balance. Fill the cup and write down the mass of water
B – Put a thermometer and support using a tripod. Put a 12V electric immersion heater into the water, ensuring that the heating element is below the water. Connect the immersion heater to a joulemeter
C – Record the temperature of the water then switch on immersion heater. Stir the cup
D – Measure the temperature change of the water and also the reading on the joulemeter
E – Once there is a significant change, stop the experiment
Part 2
A – Put a boiling tube of crushed ice into a heatproof beaker and add thermometer
B – Put the beaker onto a tripod and gauze. Pour hot water into the beaker and warm using Bunsen burner
C – Measure the temperature of the ice every minute and record results. Stop recording temperature three minutes after the ice has melted
D – Note times ice started to melt and when it had completely melted
E – Plot a graph of temperature against time. While the ice is melting at 0°C there should have been no temperature increase
Gases
Pressure of a gas is caused by gas particles colliding with the walls of the container and exerting a force. Pressure varies with volume and temperature. The higher the temperature, the higher the KE and the faster the particles move, so there are more frequent collisions with the walls of the container and there is a higher pressure. As volume decreases there is less space for particles to move so there are more collisions, increasing pressure. Volume is therefore inversely proportional to pressure
Use the equation where P = Pressure (N/m2) and V = Volume (m3)
Absolute zero is -273°C or 0K, where there is no movement of particles. To convert from Celsius to Kelvin, +273, and to convert from Kelvin to Celsius, -273.
The pressure of a gas produces a net force at right angles to any surface. Gases can be compressed or expanded by a pressure change to meet the equation below. Doing work on a gas can increase its internal energy, which increases the temperature. The gas exerts a pressure on the object, and so exerts a force. Work has to be done against this force to push down the object. This transfers KE to the gas particles, so the thermal energy and therefore the temperature increases