particle model of matter

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Melanie

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Particle theory, also known as kinetic theory, explains how particles in solids, liquids, and gases behave
Solids:
Strong forces of attraction between particles hold them close together in a fixed position to form a regular lattice structure
Definite shape and volume, cannot flow like a liquid
Particles can vibrate around, constantly jostling against each other
Heating up a solid weakens the forces between particles, at the melting point particles have enough energy to break free and the solid melts into a liquid
Liquids:
Weak forces of attraction between particles, allowing them to move around and be arranged randomly
Particles tend to stick together and are fairly compact, having a definite volume but the overall shape can change
Can flow to fit a particular container
Heating up a liquid weakens the forces holding particles together, at the boiling point particles have enough energy to break the bonds and the liquid boils or evaporates into a gas
Cooling a gas down allows particles to form bonds, condensing the gas into a liquid
Gases:
Very weak forces of attraction between particles, allowing them to move around freely
Do not keep a definite shape or volume, will always fill a container and spread out as much as possible
Gas particles move in straight lines but appear to have random motion due to traveling in any direction and being deflected randomly by solid walls and other gas particles
Heating up a gas makes particles travel faster, causing expansion if the container is expandable or an increase in pressure if the container is fixed
Changes in state within a closed system do not change the mass, as the number of particles remains the same
Solids have the highest density, liquids have slightly lower density, and gases have the lowest density of all three states
Density is a measure of how much mass a substance has per unit of its volume
To find density, divide the substance's mass by its volume
Density is measured in kilos per meter cubed in physics
Common units for density include kilos per meter cubed and grams per centimeter cubed
1 gram per centimeter cubed is equivalent to 1,000 kilos per meter cubed
Example: Aluminium has a density of 2.71 grams per centimeter cubed or 2,710 kilos per meter cubed
To calculate volume, divide mass by density
Example question: Calculate the volume of 420 kilos of aluminium with a density of 2,710 kilos per meter cubed
Volume = 420 kilos / 2,710 kilos per meter cubed = 0.155 meters cubed
To calculate the density of a solid experimentally:
Find the mass by using a balance
Find the volume by measuring the object's dimensions (for regular shapes) or using a eureka can and measuring cylinder (for irregular shapes)
To calculate the density of a liquid experimentally:
Place an empty measuring cylinder on a balance and zero it
Pour the liquid into the cylinder and record the mass
Divide the mass by the volume (in milliliters, which is equivalent to centimeters cubed) to find the density
For more accurate density measurements:
Measure larger volumes to minimize measurement uncertainties
Take multiple measurements to identify anomalies and calculate a mean
Internal energy is the total energy stored by the particles making up a substance or system
Internal energy is made up of two parts: potential energy stores and kinetic energy stores
Potential energy stores include gravitational and elastic potential energy
Kinetic energy is the movement energy of the particles and is important when heating up a substance
Heating up a substance transfers energy to the kinetic energy store of all particles, increasing their internal energy
Temperature is a measure of the average internal energy of a substance
Specific heat capacity is the amount of energy needed to raise the temperature of one kilo of a substance by one degree celsius
Specific heat capacity can also be thought of as the amount of energy released as a substance cools
The change in internal energy is equal to the mass times the specific heat capacity times the change in temperature
To find the final temperature of a substance after energy has been transferred, divide the energy by the mass times the specific heat capacity
In the example given, the final temperature of 800 grams of water after 20 kilojoules of energy has been transferred is 25.95 degrees or 26.0 degrees when rounded to three significant figures
In real life, the temperature increase might not be as much due to some energy being lost to the surroundings, mostly in the form of heat
Specific latent heat is the energy required to change one kilo of a particular substance from one state to another without changing its temperature
There are two types of specific latent heat:
Specific latent heat of vaporization: energy change when a substance changes between a liquid and a gas
Specific latent heat of fusion: energy change when a substance changes between a solid and a liquid
During a change in states, the energy provided is used to weaken or break the forces holding the particles together, rather than increasing the particle's internal energy
The temperature remains constant during a change in states until all of the substance has changed states
The equation for specific latent heat is: energy = mass of the substance x specific latent heat
To calculate the energy required to boil water, use the specific latent heat for vaporization value
For example, to completely boil 2.5 kilos of water at 100 degrees Celsius, calculate: 2.5 x 2,260,000 = 5,650,000 joules or 5,650 kilojoules
Particles in gases move about in random directions and create pressure when they collide with the walls of a container
Pressure is the force exerted per unit of area or the force divided by the area
Total pressure depends on the number of collisions and the energy of each collision
Temperature affects pressure:
Heating up a gas increases the kinetic energy of particles, causing faster movement
Faster movement leads to more collisions with the walls and each collision involves more force
Therefore, pressure increases with temperature