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)