Gases and Kinetic Theory COPY Flashcards
What was used to see Brownian motion?
Smoke particles with a microscope
What is Brownian motion?
Where particles seem to be wriggling unpredictably.
How did Brownian motion show the existanceof molecules and atoms?
The unpredictable wriggling is due to being bombarded unevenly and experiences forces due to these impacts, which changes its magnitude and direction.
What is pressure caused by?
The molecules in a gas bombarding the walls of the container
What does the graph of pressure against temperature look like?
Define absolute zero
The temperature where the pressure of an ideal gas becomes 0
Draw the graph of pressure against volume
Draw the graph of pressure against 1/volume
How would you use an experiment showing Boyle’s Law to show that P is directly proportional to 1/V
What is Boyle’s Law?
P is directly proportional to 1/V
How would you use an experiment showing Charles’s Law to that volume is proportional to temperature
What is Charles’s Law?
V is directly proportional to T
Explain how the experiment showing the pressure Law and be. used to prove P is directly proportional to T
what does the pressure law show?
P is directly proportional to T
What is the molar mass?
The mass of one mole of a gas (Mr)
What is the molecular mass?
The mass of one molecule of the gas
Define mole
The number of atoms of C-12 in 12g of C-12
What are the three gas equations (moles)?
mass = mr x mol
N = Na x mass / mr
mol = N / Na
N = No. of molecules
Na = Avagadro’s Constant
What are the three arrangements of the ideal gas equation?
pV = nRT
P1V1 / T1 = P2V2 / T2
pV = NkT
Define an ideal gas
One which obeys the equation pV = nRT at all temperatures and pressures
What are real gases
Gases that behave like ideal gases at low pressures and temperatures above room temperatures
When does an expanding gas do no work?
When it is expanding into a vacuum
What is the equation for the work done by an expanding gas at constant temperature?
W = p∆V
Why does a gas exert a force on a wall?
- The gas molecules collide elastically with the walls of the container
- Their velocity will change direction but keep the same magnitude
- This causes the component of their momentum perpendicular to the wall to change
- By Newton’s second law the molecules must have a resultant force on them to cause this change in momentum
- This resultant force is exerted by the wall on the molecules
- By Newton’s third law, if the wall puts a force on the molecules, the molecules must put an equal opposite force on the wall
- The forces from all the molecules cause a pressure on the wall, which can be calculated by P = F / A
Why does increasing the temperature of the gas increase the pressure?
- Average kinetic energy increases
- Higher average speed
- Greater rate of change of momentum when hits wall so a greater force and so greater pressure
- They also hit the wall more times per second
Why does decreasing the volume of a gas increase the pressure?
- More collisions with the container per second
- Rate of change of momentum of the particles hitting the wall will increase
- The force on the wall will increase
- So pressure will increase as pressure = F / A
Find the rms speed of molecules with speeds of 100,200,300,400,500 ms-1
rms = 331.6 ms-1
(1002 + 2002 + 3002 + 4002 + 5002) /6
How do we assume the molecules behave in an ideal gas?
- Number of molecules is very large
- Molecules are in random motion
- Forces between the gas molecules are negligible until they collide
- The collisions between the molecules and the walls are perfectly elastic
- The volume of the molecules is negligible compared to the volume of the container
- The duration of the collisions between molecules and the walls of the container and each other is negligible compared to the time between collisions
Describe what random motion is
- They have a range of speeds
- The motion of a molecule changes unpredictably
- They have no preferred direction of motion
What is a perfectly elastic collision?
A collision where they lose no kinetic energy when they collide
Derive the formula for the force on the wall exerted by one molecule of gas.
Derive the formula for kinetic theory (pressure exerted by N molecules)
Derive 1/2mc2 = 3/2kT
If you have hydrogen gas and oxygen gas at the same temperature, why does hydrogen have a huger Crms
The average kinetic energy will be the same, but the hydrogen has a lower mass so it will have a greater Crms
What will happen to the Crms if the temperature of an ideal gas is doubled
x √2
Prove that the Crms is directly proportional to the square root of the temperature.
Derive the equation for pV = NkT
