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Physics > Changes of State > Flashcards

Changes of State Flashcards

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1
Q

what can kinetic theory explain?

A

the three states of matter

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2
Q

what are the three states of matter?

A

solid, liquid, gas.

the particles of a substance in each state are the same, only the arrangement and energy of the particles are different.

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3
Q

SOLIDS

A
  • 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.
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4
Q

LIQUIDS

A
  • 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 gave more energy than the particles in a solid, they move in random directions at low speeds.
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5
Q

GASES

A
  • there are almost no forces of attraction between the particles.
  • the particles have more energy than those in liquids and solids.
  • they are free to move, and travel in random directions and at high speeds.
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6
Q

what is the thermal energy store?

A
  • the energy in a substances thermal energy store is held by its particles in their kinetic energy stores
  • this is what the thermal energy store ACTUALLY is.
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7
Q

what is boiling?

A
  • when you heat a liquid, the extra energy is transferred into the particles’ KINETIC ENERGY STORE, making them move faster
  • eventually, when enough of the particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid.
  • this is boiling.
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8
Q

what happens when you heat a solid?

A
  • the extra energy makes the particles vibrate faster until eventually the forces between them are partly overcome and the particles start to move around.
  • this is melting.
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9
Q

what happens when a substance is melting or boiling?

A
  • when a substance is melting or boiling, you’re still putting in energy, but the energy’s used for breaking intermolecular bonds rather than raising the temperature.
  • so the substance stays at a CONSTANT TEMPERATURE.
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10
Q

what happens when a substance is condensing or freezing?

A
  • when a substance is condensing or freezing, bonds are forming between particles, which releases energy.
  • this means the temperature doesn’t go down until all of the substance has changed shape.
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11
Q

what is evaporation?

A
  • evaporation is when particles escape from a liquid and become gas particles
  • particles can evaporate from a liquid at temperatures that are much lower than the liquid’s boiling point.
  • particles near the surface of a liquid can escape and become gas particles if:
    1. the particles are travelling in the right direction to escape the liquid.
    2. the particle are travelling fast enough (they have enough energy in their KE stores) to overcome the attractive forces of the other particles in the liquid.
  • the fastest particles (with the most energy) are most likely to evaporate from the liquid, so when they do, the average speed and energy in the KE stores of the remaining particles decreases
  • the decrease in average particle energy means the temperature of the remaining liquid falls, the liquid cools
  • this cooling effect can be really useful. for example, you sweat when you exercise/get hot. as the water from the sweat on your skin evaporates, it cools you down.
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12
Q

how is evaporation useful?

A
  • the decrease in average particle energy means the temperature of the remaining liquid falls, the liquid cools
  • this cooling effect can be really useful. for example, you sweat when you exercise/get hot. as the water from the sweat on your skin evaporates, it cools you down.
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13
Q

what does specific heat capacity relate?

A

specific heat capacity relates temperature and energy

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14
Q

what is temperature really a measure of?

A
  • heating a substance increases the energy in its thermal energy store.
  • so temperature is a way of measuring the average internal of a substance
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15
Q

how does it take more energy to increase the temperature of some materials than others?

A
  • e.g. you need 4200J to warm 1kg of water by 1°C, but only 139J to warm 1kg of mercury by 1°C
  • materials that need to gain lots of energy to warm up also release loads of energy when they cool down again. they store a lot of energy for a given change in temperature.
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16
Q

what is specific heat capacity?

A
  • the change in the energy stored in a substance when you heat it is related to the change in its temperature by the specific heat capacity.
  • the specific heat capacity of a substance is the energy required to change the temperature of an object by 1°C per kilogram of mass.
  • e.g. water has a specific heat capacity of 4200 J/Kg°C (pretty high)
17
Q

PRACTICAL: find the specific heat capacity of water

A
  • use a thermally insulated container to reduce energy wasted to the surroundings
    1. use a mass balance to measure the mass of the insulating container.
    2. fill the container with water an measure the mass again. the difference in mass is the mass of water in the container
    3. set up the experiment. make sure the joule meter reads zero and place a lid on the container.
    4. measure the temperature of the water, then turn on the power.
    5. when the temperature has increased by e.g. 10°C, switch off the power and record this temperature increase and the energy on the joule meter.
    6. you can then calculate the specific heat capacity of the water by rearranging the equation and plugging in the measurement
    7. repeat the whole experiment at least 3 times the calculate an average of the specific heat capacity.
18
Q

PRACTICAL: find the specific heat capacity of solids

A
  • you can follow a similar method to find the specific head capacity of a solid.
  • make sure the bloc of material you use has 2 holes in it for the heater and thermometer, and wrap it up with an insulating later
  • when you have switched off the power and finished timing, wait until the temperature has stoped increasing before recording the highest final temperature
  • this gives the energy from the heater time to spread through the solid block.
19
Q

PRACTICAL: obtain a temperature-time graph for water

A
  1. fill a beaker with crushed ice. place a thermometer into the beaker and record the temperature of the ice
  2. using the Bunsen burner, gradually heat the beaker full of ice
  3. every twenty seconds, record the temperature and the current state of the ice (e.g. partially melted, completely melted). continue this until the water begins to boil
  4. plot a graph of temperature against time for your experiment.

Physics (14 decks)

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