# physics topic 3

what are the features of a solid?
strong forces of attraction hold particles close together in a fixed regular arrangement, the particles don't have much energy so can only vibrate about their fixed positions, they have high density
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what are the features of a liquid?
weaker forces of attraction between particles close together but able to move past eachother in an irregular arrangement, particles have more energy than in a solid, particles can move in random directions at low speeds, less dense than solids
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what are the features of a gas?
almost no forces of attraction between the particles, particles have more energy than in a solid/liquid, particles are free to move in random directions at high speeds, have a low density
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what is the equation for density?
density = mass / volume
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what is meant by 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 happens when you heat a system?
energy is transferred to its particles, increaing the internal energy, leading to a change in temperature or state (size of change depends on mass, specific heat capacity, and energy input)
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what causes a substance to melt/boil?
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 causes a substance to condense/freeze?
if the substance is cooled enough, the particles will lose energy and form bonds
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what type of change is a change of state?
a physical change, meaning that you don't end up with a new substance and it's just the same substance in a different form
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what happens if you reverse a physical change?
the substance will return to its original form and get back its original properties
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what happens to the number of particles in a physical change?
the number of particles doesn't change, they're just arranged differently
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what happens when a substance is melting or boiling?
energy is being put in, but it's being used for breaking intermolecular bonds rather thana raising the temperature, shown by the flat parts on the heating graph
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what happens when a substance is condensing or freezing?
bonds are forming between particles, which releases energy, meaning that the internal energy decreases but the temperature doesn't until all the substance has turned to liquid or solid, shown by the flat parts of the cooling graph
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what is specific latent heat?
the amount of energy needed to change 1kg of a substance from one state to another, without changing its temperature
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what is specific latent heat of fusion?
the specific latent heat for changing between a solid and a liquid
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what is specific latent heat of vapourisation?
the specific latent heat for changing between a liquid and a gas
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what is the equation for energy needed/released when a substance changes state?
energy = mass x specific latent heat
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what happens if you increase the temperature of a gas?
energy is transferred into its kinetic energy stores, which increases it's average energy, so as you increase the temperature of a gas, the average speed of its particles increases
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how do gases create pressure?
gas particles move around at high speeds, so they bang into eachother and their container, when they collide with something they exert a force on it
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what is the outward gas pressure of a sealed container?
the total force exerted by all of the particles in the gas on a unit area of the container walls
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what is the relationship between pressure and volume?
p1v1 = p2v2
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how can a change in pressure of a gas change its 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, so if a container can easily change in size (cont)
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how can a change in pressure of a gas change its volume?
(cont) any change in these pressures will cause the container to compress or expand, due to the overall force
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why does a helium balloon rise if released?
atmospheric pressure decreases with height, so the pressure outside the balloon decreases, causing the balloon to expand until the pressure inside drops to the same as the atmospheric pressure
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what happens when you do work on a gas?
if you transfer energy by applying a force, then you do work, which increases its internal energy, increasing its temperature
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how can compressing a gas with a plunger increase its temperature?
you can do work on a gas mechanically: the gas applies pressure to the plunger and so exerts a force on it, work has to be done against this force to push down the plunger, which transfers energy to the kinetic energy stores, increasing temperature
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## Other cards in this set

### Card 2

#### Front

what are the features of a liquid?

#### Back

weaker forces of attraction between particles close together but able to move past eachother in an irregular arrangement, particles have more energy than in a solid, particles can move in random directions at low speeds, less dense than solids

### Card 3

#### Front

what are the features of a gas?

### Card 4

#### Front

what is the equation for density?

### Card 5

#### Front

what is meant by the internal energy of a system?