P6 Molecules and Matter Flashcards
What are solids liquids and gases?
Solid
The particles in a solid:
sit very closely together;
are in a regular arrangement and in fixed position;
vibrate about a fixed position but do not move through the solid; are held together by strong forces.
This explains why solids have a fixed shape and
volume.
Liquids
The particles in a liquid:
sit close together but some gaps have appeared;
can move past each other because of the gaps;
have enough energy to prevent the forces between them holding them in a fixed, regular arrangement;
are randomly arranged.
This explains why liquids have a fixed volume but take on the shape of their container.
Gases
The particles in a gas:
are much further apart;
are entirely free to move because the forces between them are weak;
are randomly arranged;
move quickly and randomly in all directions.
This explains why gases completely fill their container and have the same volume as their container.
How does the density change when a solid melts or when a liquid evaporates?
The particles of a solid are very close together.
It melts when it changes from the solid state to the liquid state. The particles remain close together, so there is usually only a small increase of
volume. The same mass of liquid will have slightly greater volume than the solid.
As density equals , the liquid will have slightly lower density.
A substance evaporates when it changes from the liquid state to the gas state. Its particles move freely and are very far apart, so there is a large increase of volume.
The same mass of gas will have very much greater volume than the liquid, and so will have much lower density.
What is the formula for density?
Density(ρ)=mass(m) in kg/ Volume(v) in cm^3
ρ=m/v
How to find the density of a liquid?
To measure the density of a liquid you do the same thing you would for a solid. Mass the fluid, find its volume, and divide mass by volume. To mass the fluid, weigh it in a container, pour it out, weigh the empty container, and subtract the mass of the empty container from the full container.
What is the kinetic theory of matter?
The kinetic particle model explains the properties of the different states of matter. Particles in solids, liquids and gases have different amounts of energy. The particles are arranged differently and move in different ways.
This table summarises the arrangement and movement of the particles in solids, liquids and gases and shows simple diagrams of the arrangement of the particles.
Solids- arranged closed in a regular position and vibrate around a fixed position
Liquids-arranged closed together random and they move away from each other
Gases-arranged far apart; random they move quickly in any direction
What are the changes of state processes?
Heating up
Melting - When a solid is heated, it absorbs energy and it melts, turning into a liquid.
Boiling - If the liquid is heated, it absorbs more energy and it boils, turning into a gas.
These changes absorb energy from the surroundings so they are
endothermic
.
Evaporating is when a liquid turns into a gas slowly, at temperatures that are below its
boiling point
. Puddles dry up because they
evaporate
– they don’t boil.
Cooling down
Condensing - If a gas is cooled, it transfers energy to the surroundings, and turns into a liquid.
Freezing - If the liquid is cooled, it transfers energy to the surroundings, and turns into a solid.
These changes transfer energy to the surroundings so they are
exothermic
.
Explain the heating curve of water graph
The sloped section at the start of the line , shows that the water is initially a solid (ice) at -40 °C. As the solid ice is heated, the temperature increases until it reaches its melting point of 0 °C. Once the ice reaches its melting point the line becomes horizontal , showing that the temperature does not increase during melting. Instead, the energy supplied during melting enables the particles to overcome the strong forces holding them together, allowing them to move from their fixed positions. When the melting process has finished, all the ice has become liquid water. After this, the energy transferred continues to increase the temperature of the water – shown by the second sloped section of the line.The temperature of the liquid water continues to increase as heat is added, until it reaches its boiling point of 100 °C. Again, the line becomes horizontal, showing that the temperature does not increase during boiling. The energy supplied during boiling enables the particles to overcome the forces holding them together, allowing them to escape completely from the liquid. When the boiling process has finished, all the water has become steam. Continuing to heat the steam will again increase the temperature – shown by the final sloped section of the line
*look at bbc bitesize heating curve graph
What happens to particles during heating or cooling?
When a material is heated or cooled, two changes may happen to the particles within the material:
Chemical bonds between the
particles may form, break or stretch. There is a change in the chemical potential store of energy in the material.
The material will heat up or cool down as the particles within it gain or lose speed. There is a change in the thermal store of energy within the material.
What is internal energy?
The internal energy is the total amount of
kinetic energy and chemical potential energy
of all the particles in the system.
What happens when energy is given to raise the temperature?
When energy is given to raise the
temperature
, particles speed up and gain kinetic energy.
When the substance melts or boils, energy is put in to breaking the bonds that are holding particles together, which increases the potential energy.
The
conservation of energy
means that, assuming no energy is lost to the environment, any energy transferred to a material will be distributed between the chemical store and the thermal store of the
internal energy
.
Whether the energy breaks bonds, increases the speed of the particles to stretch bonds, or just increases the speed of the particles depends on the temperature and
state
of the material.
What is specific latent heat?
Specific latent heat is the amount of energy required to change the state of 1 kilogram (kg) of a material without changing its temperature.
latent heat of fusion - the amount of energy needed to
melt or freeze the material at its melting point
latent heat of vaporisation - the amount of energy needed to boil or condense the material at its boiling point.
It is measured in J/Kg joules per kilogram.
What is the formula for change in thermal energy?
change in thermal energy = mass × specific latent heat
ΔEt=m x l
What causes gas pressure?
Since the particles in a gas are moving fast and randomly, collisions occur frequently. These collisions may be between two particles, between a particle and the wall of the container, or between a particle and something else in the container.
Gas particles in a container with arrows showing motion.
The force acting on the container due to these collisions is at right angles to the container.
For example, the collisions caused by a gas trapped inside a balloon cause forces to act outwards in all directions, giving the balloon its shape.
What is the formula for pressure?
pressure (p) is measured in newtons per metre squared (N/m2)
force (F) is measured in newtons (N)
area (a) is measured in metres squared (m2)
p=F/a
How does temperature affect gas pressure?
If the volume of a container with a gas inside stays the same, the pressure of a gas increases as its
temperature increase. As a result, the gas particles will be travelling faster and will collide with the walls of the container more frequently, and with more
force. This means that there is a
relationship between pressure and temperature. If a pressure gauge is connected to a flask of air and the flask is heated, a graph of pressure against temperature can be produced. As the temperature increases, the pressure increases showing that pressure is directly
proportional to temperature.
The temperature of a gas is a measure of the average
kinetic energy
of its particles - the higher the temperature, the higher the average kinetic energy.
