Horrocks L2 Flashcards
(25 cards)
Describe molecules in gases
In gases moelcules are far apart and weakly interacting - most of the air is empty space
Describe molecules in liquids
in liquids solute molecules jostle with solvent molecules and interactions may be string
What does the kinetic modes of gases describe
describes the behaviour of a perfect gas
What does the kinetic model of gases assumes
it assumes only the kinetic energies of the molecules contribute to the energy of the gas, so the potential energy of interactions between molecules is negligible
What are the key assumptions/observations in the kinetic model of gases
- molecules are in ceaseless random motion
- size of molecules is negligible
- diameter «_space;distance between collisions
- molecules do not interact except in elastic collisions ie translational energy of the system is conserved
What is the equation for kinetic theory
pV = 1/3xnMvrms^2
n - total number of moles of gas N/Na = n
M - mass of one mole of gas molecules = Nam
Vrms - root mean square speed of the gas molecules
What is vrms
vrms stands for root mean square speed and is a way of expressing the average speed of gas molecules in a system.
What does the maxwell Boltzmann distribution describe
Describes the distribution of particle speeds in a gas, it shows that most particles have speeds around a central value but there are some particles that move much faster or slower
What does the maxwell-Boltzmann distribution depend on
maxwell Boltzmann distribution depends on the temperature of the gas and the mass of the particles
What happens when the temperature increases in terms of maxwell Boltzmann distribution
As the temperature increases the average speed of the molecules increases and the distributions become broader
What is the equipartition principle
In every degree of freedom, there is an average thermal energy of 1/2RT
What does vm stand for
modal speed - most probable speed
What does vmean stand for
vmean - mean speed (not mean velocity)
What does vrel stand for
vrel - mean relative speed
How do we calculate the modal speed
vm = √ 2RT/M
What is the collision diameter
The collision diameter is the effective size of a molecule when it collides with another molecule in a gas. It represents the distance at which two molecules are considered to be in contact during a collision.
What is collisions frequency
Collision frequency refers to the number of collisions a single molecule or particle undergoes per unit of time in a gas.
What is collisions frequency denoted by
Z
What is Zw
Collisions flux
What is collision flux
Collision flux is the number of collisions occurring through a unit area per unit of time.
Define mean free path
The mean free path is the average distance a molecule travels before it collides with another molecule in a gas.
Describe the number of degrees of freedom for a gas molecule
each gas molecule has 3 translation degrees of freedom (motion in x,y,z directions) therefore the average mole of gas molecules is 3/2RT
How do we calculate mean free path
λ = vrel/z = KbT/σp
Vrel - mean relative speed
Z - collision frequency
Kb - boltzman constant
T - temperature
σ - collision diameter
P - pressure
What is collision diameter denoted by
σ
