5 Solids, liquids and gases Flashcards
what does kg/m3 measure
density
what does pascal measure
pressure
what does J/kg’c measure
specific heat capacity
formula for density
density = mass / volume
practical: investigate density using direct measurements of mass and volume with regularly shaped objects
Place the object on a digital balance and note down its mass
Use either the ruler, Vernier callipers or micrometre to measure the object’s dimensions (width, height, length, radius) – the apparatus will depend on the size of the object
Repeat these measurements and take an average of these readings before calculating the density
practical: investigate density using direct measurements of mass and volume with irregularly shaped objects
Place the object on a digital balance and note down its mass
Fill the eureka can with water up to a point just below the spout
Place an empty measuring cylinder below its spout
Carefully lower the object into the eureka can
Measure the volume of the displaced water in the measuring cylinder
Repeat these measurements and take an average before calculating the density
practical: investigate density using direct measurements of mass and volume with a liquid
Place an empty measuring cylinder on a digital balance and note down the mass
Fill the cylinder with the liquid and note down the volume
Note down the new reading on the digital balance
Repeat these measurements and take an average before calculating the density
formula for pressure
pressure = force / area
how does pressure at a point in a fluid act
When an object is immersed and stationary in a fluid, the fluid will exert pressure, squeezing the object
This pressure is exerted evenly across the whole surface of the fluid and in all directions
The pressure exerted on objects in fluids creates forces against surfaces
These forces act at 90 degrees (at right angles) to the surface
fluid is a liquid or a gas
equation for pressure difference
pressure difference = height x density x gravitational field strength
arrangement and motion of particles in solids
regular fixed arrangement
vibrate around a fixed position
they also have
A definite shape (they are rigid)
A definite volume
arrangement and motion of particles in liquids
randomly arranged
move around each other
liquids have
no definite shape
a definite volume
arrangement and motion of particles in gases
randomly arranged
move quickly in all directions
gases have
no definite shape or volume
changes that occur when a solid melts into a liquid
Thermal energy transfer takes place and supplies the particles in the solid with energy in their kinetic store
This breaks the rigid bonds between the particles meaning they can now flow over each other
changes that occur when a liquid evaporates or boils into a gas
Thermal energy transfer takes place and supplies the particles on the surface of the liquid with energy in their kinetic store
This removes the bonds between the particles meaning they can move about randomly and spread far apart
why does a heating system change the energy stored in it
Heating a system will change the energy stored in a system by increasing the kinetic energy of its particles
The temperature of the material, therefore, is related to the average kinetic energy of the molecules
This increase in kinetic energy (and therefore energy stored in the system) can:
Cause the temperature of the system to increase
Or, produce a change of state (solid to liquid or liquid to gas)
The higher the temperature, the higher the average kinetic energy of the molecules and vice versa
This means they move around faster
practical: obtain a temperature–time graph to show the constant temperature during a change of state
Place the ice cubes in the beaker (it should be about half full)
Place the thermometer in the beaker
Place the beaker on the tripod and gauze and slowly start to heat it using the bunsen burner
As the beaker is heated, take regular temperature measurements (e.g. at one minute intervals)
Continue this whilst the substance changes state (from solid to liquid)
what is the specific heat capacity
the energy required to change the temperature of an object by one degree celcius per Kg of mass
specific heat capacity formula
change in thermal energy = mass x specific heat capacity x change in temperature
ΔQ = m × c × ΔT
practical: investigate the specific heat capacity of materials including water and some solids
Place a polystrene cup on the digital balance and press ‘zero’
add 50g of water (50ml)
add thermometer
add an electrical heater into the water
add a lid to the cup
connect heater to power supply and add voltmeter and ammeter to circuit
switch on power supply and start timer
record values of amps and volts
once water temp has raised by 20’c stop timer and power supply
wait for water temp to stop increasing
add into formula
explain how molecules in a gas have random motion and that they exert a force, and hence a pressure, on the walls of a container
Molecules in a gas are in constant random motion at high speeds
Brownian motion provides evidence that air is made of small particles
This is because when larger particles, such as smoke particles or pollen, are observed floating in the air:
the larger particles move with random motion
this is a result of the larger particles colliding with smaller particles (which push the larger particles) that are invisible to the naked eye
As the gas particles move about randomly they collide with the walls of their containers
These collisions produce a net force at right angles to the wall of the gas container (or any surface)
and a force exerted over an area creates pressure (on the container walls)
why is there an absolute zero temperature
temperature refers to the amount of kinetic energy that the particles in the air have
so absolute 0 is where the particles have 0 energy and therefore are stationary and can’t move any slower so the temperature cannot decrease anymore
kelvin temperature
kelvin -> centigrade (-273)
centigrade -> kelvin (+273)
kelvin cannot be negative
0 kelvin is absolute 0
kelvin refers to the average amount of energy the particles have
why does an increase in temperature result in an increase in average kinetic energy of the particles
increase in temperature means each particle moves faster so gains kinetic energy. So then the particles collide more frequently with each other and the container leading to an increase in pressure
relationship between kelvin temperature and average kinetic energy of the particles
proportional
formula with pressure and kelvin temperature
T1 = T2
formula with pressure and volume
p1 x V1 = p2 x V2
relationship between pressure and volume at a constant temperature
For a fixed temperature, if the volume decreases, the pressure will increase
The particles travel the same speed as before, but the distance they travel is reduced when the container is smaller
The molecules will hit the walls of the container more frequently
This creates a larger overall net force on the walls which increases the pressure
pressure and volume are inversely proportional
relationship between pressure and kelvin temperature at a constant volume
If the temperature of the gas increases, the molecules will travel at a higher speed
This means they will collide with the walls more often
This creates an increase in pressure
pressure and temperature are proportional
