SP14: the particle model Flashcards
arrangement of particles in a solid:
-tightly packed in a regular arrangement
-vibrate about a fixed position
forces between particles in a solid:
strong
can solids keep their shape?
yes
can solids be compressed?
no
arrangement of particles in a liquid:
-particles are tightly packed but free to move past each other
-randomly arranged
-freely move around and last each other
-sit close together
can liquids keep their shape?
no
can liquids be compressed?
no
arrangement of particles in a gas:
-randomly arranged
-move quickly in all directions
-tar apart
forces between particles in a gas:
weak
can gases keep their shape?
no
can gases be compressed?
yes
density = mass/volume units
density in
mass in kg/g
volume in cm^3
when does something float?
if it is less dense than water
does hot water float on room temperature water & why?
yes as it is less dense than room temperature water
does cold water float on room temperature water & why?
no, it is less dense than room temperature water
steps of using a eureka can for irregular objects
- fill the displacement can/eureka can until the water is level with the bottom of the pipe
- place a measuring cylinder under the pipe ready to collect the displaced water
- carefully drop the object into the can and wait until no more water runs into the cylinder
- measure the volume of the displaced water
how to calculate the density of a cube
- use a ruler to measure the length (1), width (w) and height (h) of a steel cube
- calculate the volume of the cube using (I × w × h)
- place the metal cube on the balance and measure its mass
- use the measurements to calculate the density of the metal
how to calculate the density of a sphere
- use vernier callipers to measure the diameter of the sphere
- calculate the volume of the sphere using (4/3(pi)r^3)
- place the metal sphere on the balance and measure its mass
- use the measurements to calculate the density of the sphere
how to calculate the density of an irregular object
- place the object on the balance and measure its mass
- fill the displacement can/eureka can until the water is level with the bottom of the pipe
- place a measuring cylinder under the pipe ready to collect the displaced water
- carefully drop the object into the can and wait until no more water runs into the cylinder
- measure the volume of the displaced water
- use the measurements to calculate the density of the stone
how to calculate the density of a liquid
- place the measuring cylinder on the balance and measure its mass
- pour the water into the measuring cylinder
- use the measurements to calculate the density of the water
melting
solid to liquid
evaporation
liquid to gas
sublimation
solid to gas
condensation
gas to liquid
freezing
liquid to solid
what type of process is boiling?
an active process that takes energy
what type of process is evaporation?
a passive process, the liquid will slowly absorb energy from the surrounding area so that some of its particles will gain enough energy to escape the liquid
does mass change when state changes?
no
why are changes in state called physical changes?
the process can be reversed which is different to the changes seen in a chemical reaction, which cannot be reversed so easily
when a material is heated or cooled, two changes may happen to the particles within the material:
1.
-chemical bonds between the particles may form, break or stretch
-there is a change in the chemical potential store of energy in the material
2.
-particles within the material gain or lose speed
-there is a change in the thermal store of energy within the material
what happens to particles when they are heated?
particles speed up, vibrate more and gain
what happens when a substance melts or boils?
energy is put in to breaking the bonds that are holding particles together, which increases the potential energy
what is plateau?
where state changes
why is the line horizontal during changes of state?
energy is being used to break bonds
what is the conservation of energy?
energy cannot be created or destroyed, only transferred
internal energy
the sum of the kinetic and chemical potential energies of all particles in the system
kinetic energy
energy an object has due to its motion
chemical potential energy
energy stored in chemical bonds
thermal energy
the total energy of all particles in a substance
temperature
a measure of the movement of particles
what does insulation do?
stop the transfer of energy in and out
why do smaller amounts of water heat up quicker?
the smaller amount has had a bigger temperature rise because the same energy has been given to a smaller number of particles, so each particle is moving faster than those in a larger amount
specific heat capacity
the amount of energy needed to raise the temperature of 1 kg of substance by 1°C
what does a low specific heat capacity entail?
the material will warm up and cool down faster because it doesn’t take much energy to change its temperature
what does a higher specific heat capacity entail?
the material will store a large amount of energy and emit it over a long period of time
how to calculate thermal energy with specific heat capacity
mass (kg) x specific heat capacity (J/kg°C) × temperature change (°C)
how to calculate specific heat capacity?
change in thermal energy/mass x temp change
what will changing the internal energy of a material do?
cause it to change temperature or state
specific latent heat
the amount of energy needed to melt or vaporise (change the state of) 1 kg of a substance
latent heat of fusion
the amount of energy needed to freeze or melt the material at its melting point
latent heat of vaporization
the amount of energy needed to evaporate or condense the material at its boiling point
how to calculate thermal energy with specific latent heat
mass (kg) × specific latent heat (J/ kg)
how to calculate specific latent heat
energy for a change of state (J) / mass (kg)
measuring the specific heat capacity of water: method
- put a polystyrene cup in a beaker onto a balance, and zero the balance
- fill the cup almost to the top with water and write down the mass of the water
- carefully remove the cup from the balance
- put a thermometer in the water and support
- put an immersion heater into the water, making sure the heating element is completely below the water level. connect the immersion heater to a Joulemeter.
- connect your Joulemeter to the D.C side of the power pack
- record the temperature of the water, and then switch the immersion heater on. stir the water in the cup gently using the thermometer
- after five minutes, record the temperature of the water again and also write down the reading on the joulemeter
possible inaccuracies of the practical
-not all of the heat from the immersion heater will be heating up the water, some will be lost to the surroundings
-thicker insulation would improve the accuracy of the results even more
measuring the temperature of melting ice experiment: method
- place 50 grams of crushed ice straight from the freezer into the calorimeter
- place the immersion heater into the central hole at the top of the calorimeter
- clamp the thermometer with its bulb in the ice near the top of the ice
- record the temperature of the ice
- connect the heater to the power supply and joulemeter, turn it on and record the temperature every 20 seconds. continue until the thermometer bulb is no longer under the level of the water
why do collisions occur often in gases?
-the particles in a gas move fast and randomly
-collisions may be between two particles, between a particle and the wall of the container, or between a particle and something else in the container
at what angle are the forces acting on a container due to particles?
at right angles
why does a balloon have shape?
the collisions caused by a gas trapped inside a balloon cause forces to act outwards in all directions, giving the balloon its shape
how to calculate pressure (N/ m²)?
force (N) divided by area (m²)
atmospheric pressure at sea level
100,000 N/m²
if the volume of a container with
a gas inside stays the same, the pressure of a gas increases as its _____
increases
temperature
what happens when gas particles are hotter?
the gas particles will travel faster and will collide with the walls of the container more often and with more force
what is the relationship between pressure and temperature?
-directly proportional, as temperature increases pressure increases (+ kinetic energy)
-particles have more kinetic energy, they collide more and collide faster
why do some spray cans have temperature limits?
so that the pressure inside the can doesn’t increase too much and the can doesn’t explode
what is absolute zero?
the temperature when all particles stop moving (0 kelvin)
how to convert from celsius to kelvin
add 273
how to convert from kelvin to celsius
take away 273
what is the relationship between pressure and volume?
inversely proportional: if the pressure increases, the volume decreases, if pressure decreases. volume increases
what happens when pressure inside a can increases?
it explodes
what happens when pressure oUtside a can increases?
it collapses inwards
a teacher takes an empty metal oil can and puts a little water in it. she heats the can until the water starts to form steam and then screws the cap on and removes the can from the heat. after a few minutes the can suddenly crumples up. explain why this happens in as much detail as you can.
the steam inside the can condenses into water, so the pressure in the can decreases, the outside pressure is higher and the can crumples
why does pressure increase as volume decreases?
-the same number of particles collides with the walls of the container more frequently as there is less space
-the particles still collide with the same amount of force
how to convert from Pa to kPa
divide by 1000
how can pressure be increased?
- increasing the temperature - this increases the force of each collision
- decreasing the volume - this increases the number of collisions per second
forces applied to the particles in a gas result in..
a transfer of energy
what happens when someone presses a piston down on a column of gas?
-they apply a force that moves the piston a certain distance
-they have done work on the gas by compressing it
-since the volume of the gas has decreased, the pressure increases because the particles are moving in less space and collide more often
-the temperature of the gas is not fixed in most applications and the increased pressure leads to an increase in temperature
-this is because the temperature is a measure of the average kinetic energy of particles and the increase in the internal energy of the gas (as kinetic energy of the particles) means that the temperature must increase
what does mechanical work transfer energy from?
from the person/machine’s store of chemical energy to the internal energy store of the gas
