Knowt
Chapter 3: Particle Model of Matter
3.1-Density of Materials
The Particle Model can explain Density and the three states of matter
Density is a measure of the compactness of a substance. It related the mass of a substance to how much space it takes up
Density(kg/m3) = mass(kg) / volume(m3)
The density of an object depends on what it is made of and how its particles are arranged
A dense material has its particles packed tightly together.
The particles in a less dense material are more spread out-if you compressed the material, its particles would move closer together, and it would become more dense
The three states of matter are solid, liquid and gas
The states of matter all have different qualities
Solids-
strong forces of attraction hold the particles close together in a fixed, regular arrangement.
The particles don’t have much energy so they can only vibrate about their fixed positions.
The density is generally highest in this state as the particles are closest together
Liquids-
there are weaker forces of attraction between the particles.
The particles are close together, but can move past each other, and form irregular arrangements
They have more energy than the particles in a solid, and less dense than solids
Gases-
there are almost no forces of attraction between the particles.
Particles have more energy than in liquids and gases-
they’re free to move and at higher speeds.
Generally less dense
Need to measure density in different ways
Density of solid object
Use a balance to measure its mass
If it’s a regular solid, start by measuring its length, width and height with a piece of equipment(ruler).
Then calculate volume using relevant formula for the shape
For an irregular object, you can find volume by submerging it in a eureka can filled with water.
The water displaced will be transferred into a measuring cylinder
Record the volume of water in measuring cylinder
Plug the objects mass and volume into formula to find its density
Density of a liquid:
Place a measuring cylinder on a balance and zero the balance
Pour 10ml of the liquid into the measuring cylinder and record the liquids mass
Pour another 10ml into the measuring cylinder , repeating the process until the cylinder is full and recording the total volume and mass each time
For each measurement , use the formula to find the density
Finally, take an average of your calculated densities.
This gives you a value for the density of the liquid.
3.2-Internal Energy and Change of State
Internal energy is the energy stored by the particles that make up a system
The particles in a system vibrate or move around-they have energy in their kinetic energy store
They also have energy in their potential energy stores due to their positions
The energy stored in a system is stored by its particles.
The internal energy of a system is the total energy that its particles have in their kinetic and potential energy stored
Heating the system transfers energy to its particles(they gain energy in their kinetic energy stores and move faster), increasing the internal energy
This leads to a change in temperature or a change in state.
If the temperature changes, the size of the change depends on the mass of the substance, what it’s made of and the energy input.
A change in state occurs if the substance is heated enough-the particles will have enough energy in their kinetic energy stores to break the bonds holding them together
A change of state conserves mass
When you heat a liquid, it boils and becomes a gas.
When you heat a solid, it melts and becomes a liquid.
These are both changes of state.
The state can also change due to cooling.
The particles lose energy and form bonds.
The changes of states are:
A change of state is a physical change.
This means you don’t end up with a new substance-it’s the same substance as you started with, just in a different form
If you reverse a change of state, the substance will return to its original form and get back its original properties
The number of particles doesn’t change-they’re just arranged differently. This means mass is conserved-none of it is lost when the substances change state.
3.3-Specific Heat Latent
A change of state requires energy
When a substance is melting or boiling, you’re still putting in energy and so increasing the internal energy, but the energy’s used for breaking intermolecular bonds rather than raising the temperature.
There are flats spots on the heating graph where energy is being transferred but 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 doesn’t go down until all the substances has turned to liquid or a solid.
The flat parts of the graph show this energy transfer.
The energy needed to change the state of a substance is called latent heat
Specific latent heat is the energy needed to change the state of a 1kg matter
The specific latent heat of a substance is the amount of energy needed to change 1kg of it from one state to another without changing its temperature
For cooling, specific latent heat is the energy released by a change in state
Specific latent heat is different for different materials, and for changing between different states
The specific latent heat for changing between a solid and liquid is called the specific latent heat of fusion.
The specific latent heat for changing between a liquid and a gas is called the specific latent heat of vaporization
There’s a formula for specific latent heat
You can work out the energy needed when a substance of mass m changes state using this formula
Energy = Mass x Specific latent heat
Energy is given in joules, mass in kg and SLH in J/kg
3.4-Particles Motion in Gases
Average energy in kinetic stores is related to temperature
The particles in a gas are constantly moving with random directions and speeds.
If you increase the temperature of a gas, you transfer energy into the kinetic energy stores of its particles
The temperature of a gas is related to the average energy in the kinetic energy stores of the particles in the gas.
The higher the temperature, the higher the average energy
So as you increase the temperature of a gas, the average speed of its particles increases.
This is because the energy in the particles’ kinetic energy stores is 1/2mv2
Colliding gas particles create pressure
As gas particles move about at high speeds, they bang into each other and whatever else happens to get in the way.
When they collide with something, they exert a force on it.
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
Faster particles and more frequent collisions both lead to an increase in net force, and so gas pressure. Increasing temperature will increase the speed, and also the pressure
Alternatively, if temperature is constant, increasing the volume of a gas means the particles get more spread out and hit the walls of the container less often.
The gas pressure decreases
Pressure and volume are inversely proportional-when volume goes up, pressure goes down.
For a gas of fixed mass at a constant temperature, the relationship is:
pV=constant, p=pressure, v=volume
A change in pressure can cause a change in volume
The pressure of a gas causes a net outwards force at right angles to the surface of its container
There is also a force on the outside of the container due to the pressure of the gas around it
If a container can easily change its size, then any change in these pressures will cause the container to compress or expand, due to the overall force
Doing work on a gas can increase its temperature
If you transfer energy by applying a force, then you do work.
Doing work on a gas increases its internal energy, which can increase its temperature
You can do work on a gas mechanically.
The gas applies pressure to the plunger of the pump, and so exerts a force on it.
Work has to be done against this force to push down the plunger
This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature.
If the pump is connected to a tyre, you should feel it getting warmer
Chapter 3: Particle Model of Matter
3.1-Density of Materials
The Particle Model can explain Density and the three states of matter
Density is a measure of the compactness of a substance. It related the mass of a substance to how much space it takes up
Density(kg/m3) = mass(kg) / volume(m3)
The density of an object depends on what it is made of and how its particles are arranged
A dense material has its particles packed tightly together.
The particles in a less dense material are more spread out-if you compressed the material, its particles would move closer together, and it would become more dense
The three states of matter are solid, liquid and gas
The states of matter all have different qualities
Solids-
strong forces of attraction hold the particles close together in a fixed, regular arrangement.
The particles don’t have much energy so they can only vibrate about their fixed positions.
The density is generally highest in this state as the particles are closest together
Liquids-
there are weaker forces of attraction between the particles.
The particles are close together, but can move past each other, and form irregular arrangements
They have more energy than the particles in a solid, and less dense than solids
Gases-
there are almost no forces of attraction between the particles.
Particles have more energy than in liquids and gases-
they’re free to move and at higher speeds.
Generally less dense
Need to measure density in different ways
Density of solid object
Use a balance to measure its mass
If it’s a regular solid, start by measuring its length, width and height with a piece of equipment(ruler).
Then calculate volume using relevant formula for the shape
For an irregular object, you can find volume by submerging it in a eureka can filled with water.
The water displaced will be transferred into a measuring cylinder
Record the volume of water in measuring cylinder
Plug the objects mass and volume into formula to find its density
Density of a liquid:
Place a measuring cylinder on a balance and zero the balance
Pour 10ml of the liquid into the measuring cylinder and record the liquids mass
Pour another 10ml into the measuring cylinder , repeating the process until the cylinder is full and recording the total volume and mass each time
For each measurement , use the formula to find the density
Finally, take an average of your calculated densities.
This gives you a value for the density of the liquid.
3.2-Internal Energy and Change of State
Internal energy is the energy stored by the particles that make up a system
The particles in a system vibrate or move around-they have energy in their kinetic energy store
They also have energy in their potential energy stores due to their positions
The energy stored in a system is stored by its particles.
The internal energy of a system is the total energy that its particles have in their kinetic and potential energy stored
Heating the system transfers energy to its particles(they gain energy in their kinetic energy stores and move faster), increasing the internal energy
This leads to a change in temperature or a change in state.
If the temperature changes, the size of the change depends on the mass of the substance, what it’s made of and the energy input.
A change in state occurs if the substance is heated enough-the particles will have enough energy in their kinetic energy stores to break the bonds holding them together
A change of state conserves mass
When you heat a liquid, it boils and becomes a gas.
When you heat a solid, it melts and becomes a liquid.
These are both changes of state.
The state can also change due to cooling.
The particles lose energy and form bonds.
The changes of states are:
A change of state is a physical change.
This means you don’t end up with a new substance-it’s the same substance as you started with, just in a different form
If you reverse a change of state, the substance will return to its original form and get back its original properties
The number of particles doesn’t change-they’re just arranged differently. This means mass is conserved-none of it is lost when the substances change state.
3.3-Specific Heat Latent
A change of state requires energy
When a substance is melting or boiling, you’re still putting in energy and so increasing the internal energy, but the energy’s used for breaking intermolecular bonds rather than raising the temperature.
There are flats spots on the heating graph where energy is being transferred but 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 doesn’t go down until all the substances has turned to liquid or a solid.
The flat parts of the graph show this energy transfer.
The energy needed to change the state of a substance is called latent heat
Specific latent heat is the energy needed to change the state of a 1kg matter
The specific latent heat of a substance is the amount of energy needed to change 1kg of it from one state to another without changing its temperature
For cooling, specific latent heat is the energy released by a change in state
Specific latent heat is different for different materials, and for changing between different states
The specific latent heat for changing between a solid and liquid is called the specific latent heat of fusion.
The specific latent heat for changing between a liquid and a gas is called the specific latent heat of vaporization
There’s a formula for specific latent heat
You can work out the energy needed when a substance of mass m changes state using this formula
Energy = Mass x Specific latent heat
Energy is given in joules, mass in kg and SLH in J/kg
3.4-Particles Motion in Gases
Average energy in kinetic stores is related to temperature
The particles in a gas are constantly moving with random directions and speeds.
If you increase the temperature of a gas, you transfer energy into the kinetic energy stores of its particles
The temperature of a gas is related to the average energy in the kinetic energy stores of the particles in the gas.
The higher the temperature, the higher the average energy
So as you increase the temperature of a gas, the average speed of its particles increases.
This is because the energy in the particles’ kinetic energy stores is 1/2mv2
Colliding gas particles create pressure
As gas particles move about at high speeds, they bang into each other and whatever else happens to get in the way.
When they collide with something, they exert a force on it.
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
Faster particles and more frequent collisions both lead to an increase in net force, and so gas pressure. Increasing temperature will increase the speed, and also the pressure
Alternatively, if temperature is constant, increasing the volume of a gas means the particles get more spread out and hit the walls of the container less often.
The gas pressure decreases
Pressure and volume are inversely proportional-when volume goes up, pressure goes down.
For a gas of fixed mass at a constant temperature, the relationship is:
pV=constant, p=pressure, v=volume
A change in pressure can cause a change in volume
The pressure of a gas causes a net outwards force at right angles to the surface of its container
There is also a force on the outside of the container due to the pressure of the gas around it
If a container can easily change its size, then any change in these pressures will cause the container to compress or expand, due to the overall force
Doing work on a gas can increase its temperature
If you transfer energy by applying a force, then you do work.
Doing work on a gas increases its internal energy, which can increase its temperature
You can do work on a gas mechanically.
The gas applies pressure to the plunger of the pump, and so exerts a force on it.
Work has to be done against this force to push down the plunger
This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature.
If the pump is connected to a tyre, you should feel it getting warmer
