Gas Kinetics Flashcards
What is Boyle’s Law
At constant temperature, for a given sample of gas, the volume is inversely proportional to the pressure
What is the mathematical representation of Boyle’s Law
Volume is proportional to 1/P
Volume = constant/ pressure
PV= constant
P1 x V1 = P2 x V2
If a flask containing an ideal gas at a pressure of 5atm is connected to a second flask of volume 300cm3 the pressure drops to 3atm. What was the volume of the first flask
P1V1=P2V2 5xV1 = 3x(300+V1) 5V1= 3V1 + 900 2V1 = 900 V1 = 900/ 2 V1 = 450cm3
What is Charles’ Law
The volume of a given sample of gas at constant pressure is proportional to temperature
What is the mathematical representation of Charles’ Law
Volume is proportional to temperature
V1/ T1 = V2/ T2
What is Avagadro’s principle
The volume of a sample of gas at a given temperature is proportional to the number of gas molecules in the sample
What is the mathematical representation of Avagadro’s principle
Volume is proportional to number of moles (independent of which gas it is)
Volume = constant x n
What is the volume occupied by 1 mole of gas
22.4dm-3
Calculate the volume occupied by 10g CO2
No moles of CO2 x 22.4L per mole
10/44 x 22.4/1
5.2 L
What is the ideal gas law
PV = nRT
What is R and what is its value
R is the gas constant
R = 8.314 JK-1mol-1
What are the 3 assumptions of the ideal gas law
- ) gases consist of small particles which have negligible volume
- ) gas molecules are in constant rapid motion, undergoing elastic collisions with each other and their container (energy is conserved)
- ) molecules do not interact with each other except during collisions
Give experimental evidence for the ideal gas assumptions
- ) compressibility of gases
- ) Brownian motion
- ) gases expand to fill their container
Give experimental evidence against ideal gas assumptions
1) molecules have a finite mass
2) attractive interactions exists between molecules as: measured pressure
Describe experimental evidence that shows:
Measured pressure
Pressure due to collisions within container walls.
Attractive dispersion forces exist between molecules.
Molecules near walls attracted to those in bulk
Pmeasured
Why is volume of gas not negligible at high pressure
Vreal > Videal
For an ideal gas PV/RT = 1
At high pressures PV/RT > 1
Describe the deviation that occurs at moderate pressure
A negative deviation occurs due to attractive dispersion forces
What is the distribution of energies
The average kinetic energy of particles within a gas depends on the temperature, but there is a distribution of kinetic energies amongst the gas particles
What does the Zartman experiment show
That particles travel at different speed due to them hitting different sections of the second disk. Also temperature affects the speed at which particles travel
What is Maxwell-Boltzmann distribution
As temperature increases, the distribution broadens (wider range) and shifts (right) to faster average speeds
What is diffusion
The mixing of atoms of different types
What is effusion
The escape of a gas through a small hole
What is Graham’s law of effusion
At a given pressure and temperature the rate of effusion of a gas is inversely proportional to the square root of the molecular mass
What equation based on Graham’s law is used in effusion calculations
Rate of effusion of gas 1 = rate of effusion of gas 2
√(M2/M1)
Which of hydrogen and carbon dioxide will effusion faster and by how much
Rate of effusion of H2/ rate of effusion of CO2
√(44/2) = 4.7
So H2 effuses approximately 5x as fast as CO2
The rate of effusion of C2F4 is 4.6x10-6 mol hour-1. An unknown gas containing F, N, O diffuses at a rate of 6.5x10-6 mol hour-1. Deduce the formula of an unknown ga
Effusion gas 1/ effusion gas 2 = √M2/M1 = 6.5x10-6/ 4.6x10-6 = √100/M1 = 1.4squared = 100/M1 = 1.9 x M1 = 100 M1 = 100/1.9 =50 Mr = 50 F= 19, N=14, O=16 sum= 49 Gas = NOF
