particle model of matter

Question 1

what can the particle model be used to explain

Answer 1

• the different states of matter
• differences in density

Question 2

density in solids

Answer 2

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

Question 3

density in liquids

Answer 3

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

Question 4

density in gases

Answer 4

particles are very far apart so gases have relatively low density (low mass for their volume) - this is due to the negligible forces of attraction between particles

Question 5

define internal energy

Answer 5

the energy stored inside a system by the particles (atoms and molecules) that make up the system

Question 6

what happens when we heat a solid

Answer 6

we increase the internal energy of the system, and at one point, the solid undergoes melting and becomes a liquid

Question 7

what happens when we heat a liquid

Answer 7

we increase the internal energy of the system, and at one point, the liquid undergoes boiling and becomes a gas

Question 8

what happens when we cool a gas

Answer 8

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

Question 9

what happens when we cool a liquid

Answer 9

we decrease the internal energy of the system, and at one point, the gas undergoes freezing and becomes a solid

Question 10

solid -> gas

Answer 10

sublimation

Question 11

what happens when changes of state take place

Answer 11

mass is conserved; we do not add or take away any particles. however, the density of the object changes

Question 12

what type of reaction are changes of state and why

Answer 12

physical and not chemical, because the material recovers its original properties if the change is reversed

Question 13

what is internal energy the sum of

Answer 13

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

Question 14

differences between evaporation and boiling

Answer 14

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

Question 15

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

Answer 15

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

Question 16

what happens when we heat a substance

Answer 16

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

Question 17

what does the increase in temperature of a system depend on

Answer 17

the mass of the substance heated, the type of material and the energy input to the system

Question 18

define the melting point

Answer 18

the temperature at which a substance melts and freezes

Question 19

define the boiling point

Answer 19

the temperature at which a substance boils and condenses

Question 20

define latent heat

Answer 20

the energy needed for a substance to change state

Question 21

define the specific latent heat of a substance

Answer 21

the amount of energy required to change the state of one kilogram of the substance with no change in temperature

Question 22

define the specific latent heat of fusion

Answer 22

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

(solid to liquid)

Question 23

define the specific latent heat of vaporisation

Answer 23

the amount of energy required to boil one kilogram of the substance with no change in temperature

(liquid to vapour)

Question 24

define the specific heat capacity of a substance

Answer 24

the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius

Question 25

why does specific heat capacity fluctuate?

Answer 25

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)

Question 26

describe the molecules of a gas

Answer 26

the molecules of a gas are in constant random motion

Question 27

describe how changing the temperature affects gas molecules

Answer 27

an increase in temperature increases the kinetic energy of the particles, which increases the number of successful collisions

Question 28

what can you do to a gas (in relation to pressure) and what does this cause

Answer 28

a gas can be compressed or expanded by pressure changes; the pressure produces a net force at right angles to the wall of the gas container (or any surface)

Question 29

define work

Answer 29

the transfer of energy by a force

Question 30

what occurs when doing work on a gas

Answer 30

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