Particle model Flashcards
What does the kinetic theory state?
Everything is made of many small particles which are constantly moving
Describe the arrangement for solids
Forces of attraction hold the particles very closely together - they vibrate but do not move around which explains why solids can keep their shape but not be compressed
Describe the arrangement for liquids
- Particles are moving faster and so forces of attraction between the particles are not strong enough to keep the fixed position
- the particles can move past each other so liquids flow and take shape of their container
- the particles are still close together so cannot be compressed
Describe the arrangment for gases
- particles are far apart and moving around quickly
- gases are compressible and expand to fill their container
Explain how a state change is a physical change
The particles end up in a different arrangement, but the number of particles does not change (mass conservation) - no new substances are made, and the substance can recover its original properties
What is the density of a substance
The mass of a certain volume of the substance
When is a substance the most and least dense?
Most - solid
Least - gas
How do you investigate the densities of solids and liquids
- put an empty beaker on a balance and set it to 0
- use a measuring cylinder to measure 50cm3 of a liquid and pour it into a beaker and write down the reading on the balance which is the mass of 50cm3
- find the mass of the solid and write it down
- stand a displacement can on the bench with its spout over a bowl and fill it with water until the water just starts to come out the spout
- hold a cylinder under the spout and carefully drop the solid into the can and if it floats, push it down (your finger shouldn’t be in the water though)
- stand the cylinder on the bench and read the volume of the water collected which is the same as the volume of your solid
What is the formula for density?
density = mass / volume
What is thermal energy
Energy transferred to a system by heating that is stored in the movement of particles
What happens to the vibrations of the particles when the thermal energy increases?
The vibrations increase
What is the temperature a measure of?
A measure of the movement of the particles
How do you maintain a store of thermal energy
The amount of energy transferred to the surroundings by heating needs to be reduced by surrounding the warm object by insulating materials such as wool, foam or bubble wrap
What does the amount of thermal energy stored in an object depend on?
- its temperature
- its mass
- material its made of
What is the specific heat capacity of an material
The amount of energy it takes to increase the temperature of 1kg of the substance by 1 degree
When does the temperature change during a state change?
The temperature increases as more energy is being supplied to the solid, but while it’s melting, the temperature stays constant because the energy is being used to break the arrangement
What is the specific latent heat
the amount of energy it takes to make 1kg of a substance, change state
Which needs more energy, evaporation or melting?
Evaporation
How do you melt ice before finding the specific heat capacity
- Put a boiling tube full of crushed ice into a heatproof beaker and note the temperature
- Put the beaker on a tripod and gauze and pour hot water from a kettle and keep it warm using a bunsen burner
- Measure the temperature every minute and stop after three minutes when all the ice is melted
- make sure you have noted the time when the ice appeared to start melting and when it has now fully melted
How do you take the measurements for calculating the specific heat capacity
- put a polystyrene cup in a beaker on a battery scale balance note it down and then change it to 0
- add water to the cup and measure the mass
- put a thermometer in the cup and use a 12V electric heater making sure its fully submerged under the water and connect it to a joulemeter
- record the water temperature, turn on the heater and then gently stir the water using a thermometer
- after 5 minutes, check the temperature and record it also checking the joulemeter
What is the temperature of a gas a measure of?
The average kinetic energy of the particles in the gas - the faster the average speed, the higher the temperature (heating the gas increases the kinetic energy and so the temperature increases)
What is the pressure of gas based on?
Due to forces on the walls of a container caused by the moving particles hitting the walls - the faster the particles are moving, the more frequent the collisions will be and so exert more force when they collide
What does increasing the temperature of a gas do?
Increases the speed of the particles and so increases the pressure
What is the unit for pressure
Pascals (1Pa = 1 N/m^2)
What is absolute zero
The lowest temperature that is theoretically possible at which the motion of particles which constitutes heat would be minimal
What is the temperature for absolute zero
-273.15 degrees C
What does the Kelvin temperature scale measure
measures temperatures relative to absolute zero (units are kelvin) - absolute zero is 0K on the scale
How do you convert Kelvin to Celcius and vice versa
Kelvin to Celcius = subtract 273
Celcius to Kelvin = add 273
What is gas pressure?
The force exerted by gas particles colliding with the wall of their container. Gas pressure is the force exerted by a gas on a specific area.
How does gas pressure increase?
When the gas particles in a larger volume are forced into a smaller volume and so hit the walls more often and so the force on the walls increases
How does work done tie into gas pressure?
For example, when using a bicycle pump, each time you push the pump handle, the force is transferring energy to the gas inside the pump (work done)
What does elastic and inelastic meaning
Elastic - the object will return to its original shape when forces are removed
Inelastic- they will keep their new shape after the forces are removed
Give an example of an object which behaves elastically with small forces but with larger forces behaves inelastically
Metal springs (behave elastically) but if they are stretched too big they become permanently damaged
What is the extension of a spring (or another object)?
The change in length when forces are applied
What is the relationship between the extension and force
They are directly proportioanl - if the extension doubles, the force doubles
When does the relationship between the extension and force become non-linear?
When the spring is stretched too far
What is the spring constant?
The force needed to produce an extension of 1 metre
What is pressure a measure of?
The force on a unit of surface area where the force is normal (at right angles) to the surface
What is the pressure at sea level?
100 000 Pa
What does the pressure of a fluid depend on?
The depth of the fluid - the deeper you are the more weight of the fluid there is above you to exert pressure (e.g when you are at the bottom of the ocean, the pressure is high and when you are at the top of a mountain the air pressure decreases as there is less air above you)
What is atmospheric pressure due to?
The whole depth of the atmosphere above you
If you dive 10 underwater, how much pressure will you feel compared to at the surface
Double the pressure than at the surface
How many more times is water denser than the air at sea level
800
What is upthrust in a fluid due to?
Due to the difference in pressure above and below the object
What must happen to the upthrust in order for an object to float
The upthrust must be equal to the weight of the block
What happens to objects which are not equal in upthrust and weight in the block
They sink
