Solids, Liquids and Gases Flashcards
What are the units for density?
g/cm3 or kg/m3
What are the units for mass?
kg/g
What is the density of water?
1g/cm3 or 1000kg/m3
How do objects float?
If their density is less than the fluid they are in
How do you find the density of solids?
Measure the length, width and height to calculate the volume
Find the mass using a top pan balance
Density is mass/volume
How do you find the density of an irregular solid?
Calculate the volume by determining the displacement of water.
Find the mass using a top pan balance
Density is mass/volume
How to find density of a liquid?
Put liquid into measuring cylinder to find mass and volume.
Mass is the mass with liquid - mass of cylinder on its own
Density is mass/volume
How to find the density of a gas?
Fill flask with gas and using a top pan balance find mass of flask and gas. Remove gas with a vacuum and now reweigh the flask.
The change in mass is the mass of gas.
Place the flask upside down in water; water will rush up the tube to replace the removed gas. Volume of water is the volume of gas.
Density = mass/volume
What is the formula for pressure?
Pressure = force/area
What are the units for pressure?
N/m2 or N/cm2
What is another name for N/m2?
Pascals
Why must a knife be sharp to cut well?
Sharp knife has a smaller SA in contact with what it is cutting
Pressure = F/A
So if A is smaller the pressure will increase if the F is constant
Force exerted on the knife is concentrated over a smaller area and a larger pressure is exerted
Why do Inuit wear snow shoes?
The force exerted is the person’s weight
Pressure = F/A
The snowshoes increase the area in contact with the snow so the force is more spread out.
An increase in A with F constant leads to a decrease in P
What is special about the P in fluids?
It acts in all directions
What is the pressure at depth h in a fluid of density p given by?
P = hpg
What is g?
10N/kg
What is one bar?
100,000 Pa
What happens to the Magdeburg hemispheres when the air is pumped out?
Originally there is equal pressure on the inside and outside of the hemispheres; the air particles collide with the inside and outside surfaces of the spheres and so exert a significant yet equal force on either side.
When the air is removed, there is a large force on the outside pushing the spheres together as there are no air particles exerting a pressure on the inside of the spheres.
What is 1m3?
1,000,000 cm3
What means that the pressure in liquids doesn’t act in all directions?
If the liquid is moving
What happens to pressure with depth?
it increases
Properties of particles in a solid?
tightly packed
held in a fixed pattern y strong forces between them
vibrate around fixed positions
Properties of particles in a liquid?
tightly packed
not held in fixed positions
bound by strong forces between particles
move at random; Brownian motion
Properties of particles in a gas?
very spread out
move with a rapid, random Brownian motion
no fixed positions
forces between them are very weak
Why do most solids have high densities?
The particles they are made from are very closely packed in a regular arrangement.
Strong forces between the particles which give solid objects their definite shape and sometimes; much strength.
Do solid particles move?
YES! The vibrate about their fixed positions
How do gases exert a pressure?
Air particles move in Brownian motion
Random motion
Collide with wall; change direction
Change momentum
Exert a force on the wall
Pressure = F/A
As more particles collide with the wall the F increases and so pressure also increases
What is Boyle’s law?
p1V1 = p2V2
What is constant in Boyle’s law?
temperature
What is the Boyle relationship?
Pressure is inversely proportional to volume. If the pressure doubles, the volume halves.
Why does the relationship work for Boyle?
If p is inversely proportional to 1/V
then 1 = k
Therefore P x V must be k (a constant)
Why can gases be compressed?
The particles are very spread out
Why does and decrease in volume increase the pressure? PARTICLE THEORY
Temp constant - av.speed of particles is the same
If the same no of particles are squeezed into a smaller space they will collide with the walls of the container more often.
Each particle exerts a tiny force on the wall with which it collides.
More collisions/second means a greater av.F on the wall.
If P = F/A and force increases and area decreases then P increases!
What is the Temp/Press Law?
p1/T1 = p2/T2
What is the relationship between P and T?
Pressure is directly proportional to Temperature
Why is P dir.prop to T?
Volume is constant to the space they occupy is the same.
When heated, particles move randomly but with a higher av.speed. This means that they collide more frequently with the container and harder too.
They exert more Force.
If P = F/A and F increases then P also increases.
What is the relationship between Ke and temperature?
The temperature of a gas in Kelvin id proportional to the av.Ek of its particles.
Why is there no pressure at absolute zero?
The particles have no kinetic energy and so cannot collide and exert a pressure
What is absolute zero?
Temperature below which it would be impossible to cool the gas further
-273 degrees Celsius (0K)
Experiment for Boyle’s Law?
Put air in a glass tube. Add some oil.
A pump is used to increase the pressure of the oil and so reduce the volume of air.
Experiment for the Pressure Law?
Gas is enclosed in a flask with a pressure sensor so that V = constant.
Heated by placing it in a water bath and a thermometer will record the temperature of the water.
How is temperature kept constant for Boyle’s Law?
Wait a few seconds between readings
How is mass constant for Boyle’s Law?
The gas is permanently trapped between the oil and the tap of the tube so its mass is constant.
What happens to the motion of the particles in a solid when they absorb thermal energy?
Thermal energy is transferred to kinetic energy so this increase in the av.Ek of the particles causes the particles to vibrate more vigourously.
In a cooling curve, why does the rate of change of temperature decrease?
The temperature was getting closer to the temperature of the iced water and so its cooling effect was reduced.
Why doesn’t temp change when a substance is melting?
The material absorbs Therm.Energy but the Temp doesn’t rise b/c the TE used in the solid to break its bonds and melt it and is not being used to increase the temp of the substance.
What is evaporation?
vaporisation (liquid turning to gas) that occurs at the surface
What is boiling?
liquid turning to gas that occurs through the whole of the liquid
When can particles near the surface of a liquid escape and become gas particles?
If they are travelling in the right direction to escape the liquid
If they are travelling fast enough (have enough KE) to overcome the attractive forces of other particles in the liquid
Near enough to the surface
What is atmospheric pressure on Earth?
100 kPa
What is the motion of particles in a liquid?
move in random directions at low speeds
What is the motion of particles in a gas?
move in random directions at high speeds
Describe boiling
Heating a liquid gives it heat energy so particles move faster. When all the particles gain sufficient energy t overcome their attraction to each other, bubbles of gas form in the liquid
Describe melting
Heating a solid makes the particles vibrate faster until they vibrate fast enough to overcome the forces of attraction between them and they can move
What is evaporation?
when particles escape from a liquid and become gas particles
Which particles are most likely to evaporate from a liquid?
the fastest particles (most KE)
What happens when the fastest particles evaporate?
The av.speed and KE of the remaining particles decreases. This means the temperature also falls - liquid cools.
What does particles theory say?
Gases consist of very small particles constantly moving in random directions.
Particles hardly take up any space - most of gas is empty space
