Physics - Topic 3 - Particle Model of Matter

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  • Created by: hannah.o
  • Created on: 05-02-18 21:11
What is density?
Density is a measre of the compactness of a substance.
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What is the equation for density?
Density (kg/m3) = mass (kg) / Volume (m3)
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What are the three states of matter?
Solid, liquid, gas
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What is the arrangement of particles for 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.
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What is the arrangement of particles for 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 particles in a solid - move in random directions at low speeds.
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What is the arrangement of particles for gases?
There are almost no forces of attraction between the particles. The partices have more energy than in liquids and solids - they're free to move, and travel in random directions at high speeds. Have low densities.
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How do you find the density of a solid object?
1) Use a balance to measure its mass. 2) If it's a regular solid, start by measuring its length, width and height. Then calculate its volume. 3) For an irregular solid, you can find its volume by submerging it in a can filled with water.
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The water displaced by the object will be transferred to a measuring cylinder. 4) Record the volume of water in the measuring cylinder. This is the volume of the object. 5) Put the results into the density = mass / volume equation to find its density
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How do you find the density of a liquid?
1) Place a measuring cylinder on a balance and zero the balance. 2) Pour 10ml of the liquid into the measuring cylinder and record the liquid's mass. 3) Pour another 10ml into the measuring cylinder, repeating the process until the cylinder is full.
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Record the total volume and mass each time. 4) For each measurement, use the formula mass / volume to find the density. (1ml = 1cm3) 5) Take an average of the densities, this will give you a value for the density of the liquid.
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What do particles in a system do?
They vibrate or move around - they have energy in their kinetic energy stores. They also have energy in their potential energy stores due to their positions.
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What is the internal energy of a system?
The total energy that its particles have in their kinetic and potential energy stores.
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What does heating the system do?
Heating the system transfers energy to its particles (they gain energy in their kinetic stores and move faster), increasing the internal energy. This leads to a change in temp or state.
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What happens 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.
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When does a change in state occur?
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.
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What are the changes of state?
Solid > liquid = melting. Liquid > solid = freezing. Liquid > gas = boiling/evaporating. Gas > liquid = condensing. Solid > gas = sublimating
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What is a change of state?
A physical change which means you don't end up with a new substance - it's the same substance as you started with, just in a different form.
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What happens if you reverse a change of state?
The substance will return to its original form and get back its original properties.
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What doesn't change with a change of state?
The number of particles - they're just arranged differently. This means mass is conserved - none of it is lost when the substance changes state.
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What does a change of state require?
Energy - when a substance is melting or boiling, you're still putting in energy and so increasing the internal energy, but the energy is used for breaking intermolecular bonds rather than raising the temp.
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What does this melting/boiling graph look like?
.
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Why are there flat spots on the graph?
It is where energy is being transferred by heating but not being used to change the temperature.
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What happens when a substance in condensing or freezing?
Bonds are forming between partices, which releases energy. This means the internal energy decreases, but the temperature doesn't go down until all the substance has turned to liquid or a solid. The flat parts of the graph show this energy transfer.
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What does this condensing/freezing graph look like?
.
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What is specific latent heat?
The specific latent heat (SLH) of a substance is the amount of energy needed to change 1kg of it from one state to another without changing its temperature.
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What is the SLH for changing between a solid and a liquid called?
Specific latent heat of fusion.
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What is the SLH for changing between a liquid and a gas called?
Specific latent heat of vaporisation.
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What is the equation that SLH is involved in?
Energy (E) = mass (m) x Specific latent heat (L)
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What are the units for SLH?
J/kg
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What does the particle model do?
It helps explain how temperature, pressure, volume and energy in kinetic stores are all related.
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What happens when you increase the temperature of a gas? (2)
Since the particles in a gas are constantly moving with random directions and speeds, when the temp is increased, you tranfer energy into the kinetic energy stores of its particles. The temperature of a gas is related to the average energy in the
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kinetic energy stores of the particles in the gas. The higher the temperature, the higher the average energy. So as you increases the temperature of a gas, the average speed of its particles increases.
This is because the energy in the particles' kinetic energy store is 1/2mv2.
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How do gas particles create pressure?
As gas particles move at high speeds, they bang into each other. When they collide, they exert a force and so a pressure. Sealed container, the outward gas pressure is the total force exerted by all particles in gas on a unit area of container walls.
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How does the gas pressure increase?
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 so the pressure (if volume is kept constant).
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How does the gas pressure decrease?
If temperature is constant, increasing the volume of a gas means the paarticles get more spread out and hit the walls of the container less often, therefore the gas pressure decreases.
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What are pressure and volume?
Inversely proportional - when volume goes up, pressure goes down and when volume decreases, pressure increases).
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What is the relationship for a gas of fixed mass at a constant temperature?
pV = constant
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What does the pressure of a gas cause?
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.
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What happens if a container can easily change its size (e.g. balloon)?
Then any change in these pressures will causes the container to compress or expand, due to the overall force.
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What does doing work on a gas cause?
Doing work on a gas increases its internal energy, which can increase its temperature.
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Card 4

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Card 5

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