PARTIAL PRESSURES AND DALTON'S LAW Flashcards
- How do gases behave when in a mixture with other gases?
- the individual pressures are all added to each other
- this presents us with a total pressure
∴ P total = P1 + P2 + P3 …
- How do gases behave when they are mixed with other gases?
- they behave as though they are alone
- this is a result of the absence of interactions
- How is the concentration of any specific gas in a mixture worked out?
- using the mole fraction (X)
- How would we calculate the pressure of the Earth’s Atmosphere?
- What is the Kinetic-Molecular Theory?
- a gas consists of tiny particles
- these particles are moving around randomly
- the gas particles act independently of each other
- there are no attractive or repulsive forces between
them
- Within the Kinetic Molecular Theory of Gases, what kind of collisions are happening between gas particles?
- elastic collisions
- kinetic energy is conserved
- momentum is conserved
- kinetic energy is not lost
- the kinetic energy is transferred
- Within Kinetic Molecular Theory, what is the average kinetic energy of gas particles proportional to?
- the Kelvin Temperature
AVERAGE:
- not all the particles have the same speed
- speed goes to zero when particles collide
- this speed will stay at zero until something else
collides with the particles
- there is a disruption of speeds for given molecules
- What curve is seen in this diagram?
- Boltzmann curve
- these are the curves of different gases at constant
temperatures
- What can be noticed in this curve?
- the different molecules will move at different speeds
- the temperature for all gases is constant and fixed
- H2 has the highest average speed
- this is because it has the lowest mass
- light gases will move a faster speeds
- kinetic energy is proportional to speed
- What do the letters of the equation represent?
u = average molecular speed
3RT = 3 x gas constant x Kelvin Temperature
M = mass of each molecule
- Where is the average speed of the gas particles situated?
- the average speed of the gas particles is slightly to the
right of the peak of the curve - the average speed depends on the mass of the gas
particles
- What happens when the gas particles have an increased mass?
- the the gas particles have a lower average sped
- Oxygen is the heaviest molecule
- this is why it has the lowest average speed
- How can we relate Boyle’s Law to the Kinetic Molecular Theory to explain Gas Behaviour?
IF WE REDUCE THE VOLUME:
- the particles will collide
more frequently with the
walls
- this will increase the
pressure
- this is because the pressure
depends on the frequency
and the intensity of the
collisions
- How can we relate Charles’ Law to the Kinetic Molecular Theory to explain Gas Behaviour?
WHEN THE TEMPERATURE INCREASES:
- the kinetic energy of the
particles increases
- the particles are now moving
faster
IN ORDER TO MAINTAIN CONSTANT PRESSURE:
- which is a requirement for
Charles’ Law
- the container size needs to
expand
- this will increase the volume
- the particles will be hitting the
walls with a higher intensity
- the expanded volume
decreases the frequency of the
collisions
- this keeps the pressure
constant
- How can we relate Avogadro’s Law to the Kinetic Molecular Theory to explain Gas Behaviours?
THE AMOUNT OF GAS INCREASES:
- the collisions with the wall tend to become more
frequent
- the container must expand
- this lowers the frequency of the collisions
- this maintains the pressure constant
- constant pressure is necessary for Avogadro’s Law
- What is Diffusion?
- this is the process by which two different gases mix
together - this is done by random molecular motion with
frequent collisions
- What is going on the diagram?
- the Hydrogen particles are diffusing faster
- this is because they are smaller
- these particles have a lower molecular mass
- How is Entropy present in the last step of the diagram?
- the particles are more disordered
- this is because there is a natural tendency for things
to become more disordered - nature detests order
- What is Effusion?
- this is the process by which gas escapes through a
pinhole - this leads to a vacuum
- or into a region of lower pressure
- What does Graham’s Law mathematically state?
- the rate of effusion or diffusion is inversely
proportional to the square root of the mass
of the substance
- How would we mathematically figure out the
relation between the rates and the masses of two
different gases?
- the gas with the lowest mass escapes more easily
- the gas with the highest mass escapes with more
difficulty
22: The molecular mass of the Ammonia is
17g/mol.
: The molecular mass of the HCl is 36.5 g/mol
∴Which has diffuses faster?
- Ammonia
- this is a direct result of its lighter gas particles
23: The molecular mass of the Ammonia is
17g/mol.
: The molecular mass of the HCl is 36.5 g/mol
∴What is seen on the left hand side of the tube?
- a cotton ball dipped in NH4OH (aq) solution
- this will give off NH3 gas particles
NH3 = Ammonia
24: The molecular mass of the Ammonia is
17g/mol.
: The molecular mass of the HCl is 36.5 g/mol
∴What is seen on the right hand side of the tube?
- a cotton ball dipped in Hydrochloric Acid (HCl)
- the cotton ball will off HCl particles
25: The molecular mass of the Ammonia is
17g/mol.
: The molecular mass of the HCl is 36.5 g/mol
∴What happens within the tube when the NH3
and the HCL particles diffuse?
- the NH3 particles start moving to the right
- the HCL particles start moving to the left
- the lighter NH3 particles move much faster
26: The molecular mass of the Ammonia is
17g/mol.
: The molecular mass of the HCl is 36.5 g/mol
∴What happens within the tube when the NH3
and the HCL particles meet?
- they form a white smoke
- this smoke is made of NH4Cl
- the white smoke will form to the right of the middle of
the tube
- What does the Ideal Gas Law require to work?
- large distances between the gas particles
- When does the Ideal Gas Law fail?
- when the gas particles get too close together
- this lack of space allows there to be interactions
between the particles - this will happen at a high pressure
- and a low temperature
THE IDEAL GAS LAW WILL ALSO FAIL WHEN:
- the size of the gas particles becomes very large
- this assumes that the gas particles are points with no
volume
- What two factors become important when there is a close contact of Gas Particles?
- finite volume of the gas
- intermolecular attractive forces
- Which equation describes Real Gas Behaviour?
- the Van Der Waals Equation
- What is the Van Der Waals Equation?
- nb = the bigger the molecule
= the bigger the volume concentration - an² = this is related to the intermolecular forces that
exist between gas molecules
- What does this table describe?
- this table consists of ‘a’ and ‘b’ factors
- these are found in the Van Der Waals equations for
real gases
- What does the constant ‘a’ relate to?
- it relates to the magnitude of intermolecular forces
within the molecule
- Which molecules have a large ‘a’ constant?
- Heavy CCl4
- this has large London Dispersion Forces
- Water Molecule
- it has hydrogen bonds
- Which molecules have a large ‘a’ constant?
- Heavy CCl4
- this has large London Dispersion Forces
- Water Molecule
- it has hydrogen bonds
- What is the constant ‘b’ related to?
- it is related to the size of the molecule
- Which molecule has the largest ‘b’ constant?
- CCl4
- it is the largest molecule
- Which molecule has the smallest ‘b’ constant?
- He
- it is the smallest molecule
- What happens when the molecule is heavier and polar?
THE HEAVIER THE MOLECULE:
- the more electrons are present
- the more Inter molecular forces are present
POLAR MOLECULES:
- have more inter molecular forces
- Answer this question?
E.
- the smallest ‘b’ constant will belong to the smallest
sized molecule
- this is H2
- Read through the summary.
Does this make sense?
- yes
