molecules and matter Flashcards
What can the particle model be used to explain?
- the different states of matter
- differences in density
Define density
- mass per unit volume density
- density = mass/volume
What does density depend on?
- spacing of atoms in matter
Describe density in solids
- 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
Describe density in liquids
- 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
Describe density in gases
- 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
Define internal energy
- 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)
What happens when a solid is heated up?
- 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
What happens when a liquid is heated up?
- the internal energy of the system increases
- and at one point
- the liquid undergoes boiling and becomes a gas
What happens when a liquid is cooled down?
- the internal energy of the system decreases
- and at one point, the gas undergoes freezing and becomes a solid
What happens when a gas is cooled down?
- we decrease the internal energy of the system
- and at one point, the gas undergoes condensation and becomes a liquid
Name the change of state from solid to gas
- sublimation
What happens when changes of state take place?
- mass is conserved
- however, the density of the object changes
What type of reaction are changes of state and why?
- physical change (which are reversible)
- because the material recovers its original properties if the change is reversed
What is internal energy the sum of?
- the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system
Name the differences between evaporation and boiling
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
On a heating and cooling graph, why does the temperature stop rising and become horizontal?
- 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
What happens when we heat a substance?
- 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
What does the increase in temperature of a system depend on?
- the mass of the substance heated
- the type of material and the energy input to the system
Define the melting point
- the temperature at which a substance melts and freezes
Define the boiling point
- the temperature at which a substance boils and condenses
Define latent heat
- the energy needed for a substance to change state
Define the specific latent heat of a substance
- the amount of energy required to change the state of one kilogram of the substance with no change in temperature
Define the specific latent heat of fusion
- 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)
Define the specific latent heat of vaporisation
- the amount of energy required to boil one kilogram of the substance with no change in temperature
- (energy to boil/condense)
What happens during melting & evaporating in terms of energy?
- energy is absorbed
What happens during freezing and condensing in terms of energy?
- energy is released
Define the specific heat capacity of a substance
- the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius
Why does specific heat capacity fluctuate?
- 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)
Describe the molecules of a gas
- the molecules of a gas are in constant random motion
Describe how changing the temperature affects gas molecules
- an increase in temperature increases the kinetic energy of the particles
- which increases the number of successful collisions
Describe the relationship between temperature and kinetic energy of gas molecules
- the higher the temp, the greater the average kinetic energy and so faster the average speed of the molecules
What happens when the molecules collide with the wall of their container?
- they exert a force on the wall
Define gas pressure
- the total force exerted by all of the molecules inside the container on a unit area of the walls
What happens when you change the temp of a gas held at a constant volume?
- changing temp of a gas at a constant volume changes the pressure entered by the gas (Pressure law)
What can you do to a gas (in relation to pressure)?
- a gas can be compressed or expanded by pressure changes;
What happens when a gas is compressed/expanded?
- the pressure produces a net force at right angles to the wall of the gas container (or any surface)
What can happen when you increase the volume in which a gas is contained?
- 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
Define work
- the transfer of energy by a force
What occurs when doing work on a gas?
- the internal energy of the gas increases and can cause an increase in the temperature of the gas
