Gaseous State Flashcards
What are the assumptions for kinetic theory?
- gas particles are in constant random motion
*** gas particles have negligible volume compared to the volume of the container - gas particles exert negligible intermolecular forces on one another**
- collisions between gas particles are perfectly elastic
- average kinetic energy of particles is directly proportional to absolute temperature
What does the pressure of gas depend on?
- frequency of collisions
- speed at which particles are colliding against the wall
What is the pressure on earth at sea level?
- 1atm = 101325Pa or Nm⁻²
- 760mm Hg
How to convert dm³ to m³?
1dm³ = 10⁻³ m³
How to convert cm³ to m³?
1cm³ = 10⁻⁶ m³
How to convert 1 bar to 1Pa?
1 bar = 100 000Pa
What is Boyle’s law?
- At constant temperature, the volume of a fixed volume of gas is inversely proportional to its pressure
- V ∝ 1/p
- pV = constant, p1V1 = p2V2
What does the V against p graph of a fixed mass of gas at constant temperature look like?
- curve downward sloping with decreasing gradient
- 1/x graph
What does v against 1/p graph look like for a fixed mass of gas at constant temperature?
straight line that passes through origin
What does pV against p graph look like for a fixed mass of gas at constant temperature?
horizontal straight line
What is Charles’ law?
- At constant pressure, the volume of a fixed mass of gas is directly proportional to the absolute temperature
- V ∝ T
- V/T = constant, V1/T1 = V2/T2
What does a V against T (in K) graph for a fixed mass of gas at constant pressure look like?
straight line that passes through origin
What does a V against T (in °C) graph for a fixed mass of gas at constant pressure look like?
Straight line with x-intercept at -273°C
What is Avogadro’s law?
- At constant temperature and pressure, the volume of gas is directly proportional to the number of moles of the gas
- V ∝ n
- V/n = constant, V1/n1 = V2/n2
What is partial pressure?
Pressure that the gas would exert as if it occupied the container alone under the same conditions
What is Dalton’s law of partial pressure?
The total pressure of a mixture of non-reacting gases equals the sum of partial pressures exerted by constituent gases
What is Dalton’s law of partial pressure’s formula?
P(total) = Pa + Pb + Pc + …
What is the formula for partial pressure?
pₐ = (nₐ/nₜₒₜₐₗ) × pₜₒₜₐₗ
How do we know if a gas is “ideal”?
For 1 mol of ideal gas, n=pV/RT = 1 at all pressures
At what condtions do real gas deviate more from ideal behaviour?
- high pressures
- low temperatures
What kind of gas particles deviate more from ideal gas behaviour and why?
- large electron cloud
- polar
How does gas particles with large electron cloud affect their ideal behaviour?
- strength (due to larger number of electrons) and extensiveness (due to larger surface area) of intermolecular forces between gas particles would be more significant
- volume of larger gas particles would be more significant when compared to the volume of the container
How do polar molecules affect their ideal gas behaviour?
intermolecular forces (pd-pd or hydrogen bonding) would be stronger compared to weaker id-id between non-polar molecules of similar Mr
Under what conditons do real gas approach ideal behaviour?
- low pressure
- high temperature
Why does a real gas approach ideal behaviour at low pressure and high temperature?
- At low pressure, gas occupies a large volume and thus the volume of gas particles is negligible compared to the volume of the container, intermolecular forces of attraction would also be negligible as the particles are far apart
- At high temperature, particles have high kinetic energy and hence have sufficient energy to overcome the intermolecular forces of attraction
Why is there differing speed for gas particles?
consider what happens at same temperature
- at the same temperature, all particles in a sample of gas have the same kinetic energy and hence average speed but the individual particles do not have the same speed
- due to collisions (between particles and wall of container), there will be a large range of speed at any given moment in a sample of gas
What does the area under the curve for Maxwell-Boltzmann distribution represent?
total number of gas particles
What does peak of each curve of Maxwell Boltzmann distribution curve represent?
most probable speed, v or most probable energy, E
What happens to the Maxwell-Boltzmann distribution curve when temperature increases?
- peak of the curve shifts right (most probable speed increases)
- curve flattens (more particles have high energy and less have low energy)
- area under the curve is same for total number of particles is the same
What is the axis of Maxwell-Boltzmann distribution curve?
- y-axis: Number of particles with energy, E
- x-axis: speed (or energy)
What does the distribution of speed in Maxwell-Boltzmann distribution curve depend on?
- temperature
- mass of particle
How does mass of particle affect the Maxwell-Boltzmann distribution curve?
- particles with lower masses have higher average speed
- most probable speed (peak will be higher)
