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ZZ Phys 1 > molecules and matter > Flashcards

molecules and matter Flashcards

1
Q

What can the particle model be used to explain?

A
  • the different states of matter
  • differences in density
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2
Q

Define density

A
  • mass per unit volume density
  • density = mass/volume
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3
Q

What does density depend on?

A
  • spacing of atoms in matter
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4
Q

Describe density in solids

A
  • the particles are very close together so solids have a high density (high mass for their volume)
  • this is due to the strong forces of attraction between particles
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5
Q

Describe density in liquids

A
  • the particles are still relatively close together so liquids have a relatively high density (high mass for their volume)
  • this is due to relatively strong forces of attraction between particles, but these are weaker than solids
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6
Q

Describe density in gases

A
  • particles are very far apart (spacing increase x10) so gases have relatively low density (low mass for their volume)
  • this is due to the negligible forces of attraction between particles and particles have lots of energy to move therefor volume increases greatly
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7
Q

Define internal energy

A
  • the energy stored inside a system by the particles (atoms and molecules) that make up the system
  • takes the form of kinetic energy (vibration of atoms) and potential energy (between particles)
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8
Q

What happens when a solid is heated up?

A
  • the internal energy of the system increase as it increases the energy the particles have
  • this can either raise temp of stem or produce a change of state
  • and at one point, the solid undergoes melting and becomes a liquid
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9
Q

What happens when a liquid is heated up?

A
  • the internal energy of the system increases
  • and at one point
  • the liquid undergoes boiling and becomes a gas
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10
Q

What happens when a liquid is cooled down?

A
  • the internal energy of the system decreases
  • and at one point, the gas undergoes freezing and becomes a solid
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11
Q

What happens when a gas is cooled down?

A
  • we decrease the internal energy of the system
  • and at one point, the gas undergoes condensation and becomes a liquid
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12
Q

Name the change of state from solid to gas

A
  • sublimation
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13
Q

What happens when changes of state take place?

A
  • mass is conserved
  • however, the density of the object changes
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14
Q

What type of reaction are changes of state and why?

A
  • physical change (which are reversible)
  • because the material recovers its original properties if the change is reversed
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15
Q

What is internal energy the sum of?

A
  • the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system
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16
Q

Name the differences between evaporation and boiling

A

EVAPORATION
* only the particles on the surface have enough energy to escape the liquid as a gas
* can take place below the boiling point
* slower process
* no bubbles produced
* leads to cooling
BOILING:
* occurs throughout the liquid
* faster process
* produces bubbles
* does not lead to cooling

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17
Q

On a heating and cooling graph, why does the temperature stop rising and become horizontal?

A
  • the substance is undergoing a change of state
  • during this process, the heat is transferring energy to the potential energy stores of the particles but not the kinetic energy stores
  • the energy is being used to break the forces of attraction to change state, rather than to increase the temperature
18
Q

What happens when we heat a substance?

A
  • we change the energy stored within the system by increasing the energy of the particles that make up the system.
  • this either raises the temperature of the system or produces a change of state
19
Q

What does the increase in temperature of a system depend on?

A
  • the mass of the substance heated
  • the type of material and the energy input to the system
20
Q

Define the melting point

A
  • the temperature at which a substance melts and freezes
21
Q

Define the boiling point

A
  • the temperature at which a substance boils and condenses
22
Q

Define latent heat

A
  • the energy needed for a substance to change state
23
Q

Define the specific latent heat of a substance

A
  • the amount of energy required to change the state of one kilogram of the substance with no change in temperature
24
Q

Define the specific latent heat of fusion

A
  • the amount of energy required to melt one kilogram of the substance with no change in temperature
  • e.g. it takes 334000J of energy to melt 1kg of ice, so that is its specific latent heat of fusion
  • (energy to melt/freeze)
25
Q

Define the specific latent heat of vaporisation

A
  • the amount of energy required to boil one kilogram of the substance with no change in temperature
  • (energy to boil/condense)
26
Q

What happens during melting & evaporating in terms of energy?

A
  • energy is absorbed
27
Q

What happens during freezing and condensing in terms of energy?

A
  • energy is released
28
Q

Define the specific heat capacity of a substance

A
  • the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius
29
Q

Why does specific heat capacity fluctuate?

A
  • some substances require more energy to raise their temperature than others
  • e.g. sand is usually hotter than the sea because water has a higher specific heat capacity (so more energy is needed to heat 1kg by 1 degree)
30
Q

Describe the molecules of a gas

A
  • the molecules of a gas are in constant random motion
31
Q

Describe how changing the temperature affects gas molecules

A
  • an increase in temperature increases the kinetic energy of the particles
  • which increases the number of successful collisions
32
Q

Describe the relationship between temperature and kinetic energy of gas molecules

A
  • the higher the temp, the greater the average kinetic energy and so faster the average speed of the molecules
33
Q

What happens when the molecules collide with the wall of their container?

A
  • they exert a force on the wall
34
Q

Define gas pressure

A
  • the total force exerted by all of the molecules inside the container on a unit area of the walls
35
Q

What happens when you change the temp of a gas held at a constant volume?

A
  • changing temp of a gas at a constant volume changes the pressure entered by the gas (Pressure law)
36
Q

What can you do to a gas (in relation to pressure)?

A
  • a gas can be compressed or expanded by pressure changes;
37
Q

What happens when a gas is compressed/expanded?

A
  • the pressure produces a net force at right angles to the wall of the gas container (or any surface)
38
Q

What can happen when you increase the volume in which a gas is contained?

A
  • increasing the volume in which a gas is contained, at a constant temp, can lead to a decrease in pressure (Boyle’s law) due to the reduce number of collision per unit area
39
Q

Define work

A
  • the transfer of energy by a force
40
Q

What occurs when doing work on a gas?

A
  • the internal energy of the gas increases and can cause an increase in the temperature of the gas

ZZ Phys 1 (5 decks)

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