Physics - Topic 3 - Particle Model of Matter (Particle Motion In Gases…
Physics - Topic 3 - Particle Model of Matter
Density of Materials
The Particle Model can Explain Density and the Three states of matter
The Density of an object depends on what it's made of and how its particles are arranged.
Density(kg/m^3) =Mass(kg) / volume(m^3)
A dense material has its particles packed tightly together. The particles in a less dense material are more spread out, a compressed material is more dense but still the same mass.
Liquids - Weaker forces of attraction between the particles, close tighter but can move past eachother to form a irregular arrangement. More energy and move randomly at low speeds, less dense.
Gases - Almost no forces of attraction, have the most energy and are free to move, travel at high speeds, low densities.
Solids - string force of attraction, fixed, regular arrangement, not a lot of energy, high density.
Specific Latent Heat
Specific Latent Heat is The Needed to Change the state of a 1kg mass.
SLG if a substance is the amount of energy needed to change the 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 heart is different for different materials and for changing between different states.
The specific latent heat for changing between a solid and liquid (melting or freezing) is called the SLH of fusion. The SLH for changing between a liquid and a gas(evaporating, boiling or condensing) is called the SLH of vaporisation.
There's a formula for Specific Latent Heat
Energy(J) = Mass(KG) x Specific latent heat(J/kg)
A Change of state Requires Energy
When a substance is condensing or freezing , binds are forming between particles which releases energy, this means the internal energy decrease but the temp docent go down until all the substance has turned to liquid or solid.
The energy needed to change the state of a substance is called latent heat.
When a substance is melting or boiling, you're putting energy and so increasing the internal energy, the energy is used for breaking intermolecular bonds rather than raising the temp.
Particle Motion In Gases
Colliding Gas Particles Create Pressure
As particles move at high speeds, they collide with each other and whatever is in the way. This means they exert a force onto the object they hit.. In a sealed container the outward gas pressure is the total force exerted by the particles colliding with the walls and one another.
Faster particles and more frequent collisions both lead to a net force increase. and so the gas pressure. Increasing the temp will do the same so long volume is kept constant.
If the temp is constant, increasing the volume of a gas means the particles in the gas are more spread out and hit the walls less. Gas pressure decreases
Pressure and volume are inversely proportional. When one goes up the other goes down. pV=constant
A Change in Pressure can Cause a Change in Volume
There is also a force on the
of the container due to the pressure of the gas
If a container can change size easily e.g a balloon. then any change in these pressures will cause an expansion or a compression due to the overall force.
The pressure of a gas causes a net outward force at
to the surface of its container
is related to
The temperature is related to the average energy in the kinetic stores of the particles (of a gas). The higher the temp, the higher the average energy.
So as you increase the temp of a gas, the average speed increases.. 1/1mv^2
The particle move in random directions and speed. Increasing the temperature also increases their kinetic energy store
on a Gas Can Increase Its Temperature
If you transfer energy by applying a force, then you do work. Doing work on a gas increase its internal energy. which increase the temp.
You can do work on a gas mechanically, e.g bike pumps. The gas applies pressure to the plunger of the pumps, exerting a force on it. Work has to be done done against this force to push down the plunger.
This transfer energy to the kinetic energy stores of the gas particles, increasing the temp. If the pump is connected tot he tyre , it can be felt getting warmer
Internal Energy and Changes of State
Internal Energy is the Energy Stored by the Particles That make up a System
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 stores.
Heating the system transfers energy to its particles, increasing the internal energy.
They have energy in their potential energy stores due to their positions.
Leads to a change in temp or state, if the temp changers the size of change depends on its mass, what its made off and the energy input.
The particles in a system vibrate or move around - they have energy kinetic energy stores.
A change in state occurs if the substance is heated enough - the particles will have enough energy in there kinetic energy stores to break the bonds holding them together.
A Change of State Conserves Mass
Change of states are
Liquid to Solid - Freezing , Liquid to Gas - boiling or evaporating
Gas to liquid - Condensing
Solid to Liquid - Melting , Solid to Gas - Sublimating
A change of state is a physical change - means no new substance just the same one in a different form.
The state can also change die to cooling. The particles lose energy and form bonds.
If you reverse a change of state the substance will return to its original form and get back its original properties.
When you heat a liquid it boils and becomes a gas, when you heat a solid it melts and becomes a liquid.
The number of particles do not change just are arranged differently.