4.2 Thermal Physics Flashcards
Define Boyle’s Law
For a fixed mass of gas at constant temperature, the volume (V) is inversely proportional to the applied pressure (p)
What is the Boyle’s law equation
pV = a constant where p is in Pascals
Define Charles’ Law
For a fixed mass of gas at constant pressure, the volume (V) is directly proportional to the kelvin temperature (T)
What is the Charles’ Law equation
V/T = a constant
Define the Pressure Law
For a fixed mass of gas at constant volume, the pressure (p) is directly proportional to the kelvin (or absolute) temperature (T)
What is the Pressure Law equation
P/T = a constant
What is the ideal gas equation
pV/T = a constant or pV=nRT (n = no. moles in gas) or. pV = NkT (N = no. molecules of gas)
what does the ideal gas equation depend on
a constant no. molecules in the sample of gas considered
Define a mole
The mole is the amount of substance which contains as many particles as there are atoms in 0.012kg of carbon 12
Define avogadros number
the number of particles per mole
what is avogadros number
6.02 x 10^23
equation for the number of moles in a substacne
no. particles/avogadros no.
what is the relative molecular mass
mass of 1 mol in grams
equation for the relative molecular mass
RMM = mass of gas sample in grams/no.moles
Define kinetic theory
it is the collision of gas molecules with the walls of a container the produce an outward force or pressure
What are the 5 assumptions of kinetic theory
- There are no intermolecular forces
- the molecules themselves have a negligible volume compared to the volume of the gas
- the collisions between molecules and the walls of the container are elastic (i.e. energy is conserved)
- the duration of a collision is negligible when compared w the time between collision
- between collisions molecules move with constant velocity
the total force on the container walls is the
sum of the forces of all colliding molecules
Explain Boyle’s Law in terms of kinetic theory
a reduced volume means that the molecules have a shorter distance to travel to the walls of the container. Thus more collisions occur per second. Pressure increases
explain Charles’ Law in terms of kinetic theory
Increase in temp means ke, momentum and velocity of the molecules all increase
to maintain same pressure, no. collisions per second decreases
expansion (increased volume) leads to a greater distance between collisions
longer time interval thus leads to a decreased no. collisions per second and pressure remains constant
explain the pressure law in terms of kinetic theory
Increase in temp means ke, momentum and velocity increase
momentum change per collision and no.collisions per s increases
pressure increases
what is R
the universal gas constant (applies to all gases)
8.31 Jmol^-1K^-1
What is the Boltzmann constant, k
1.88 x 10^-23
what is the equation for the Boltzmann constant, k
k = R/Avogadro’s no
define translational kinetic energy
the kinetic energy of straight line motion is the only energy possessed by the atoms
Define the internal energy of a gas
the internal energy of a real gas is the sum of the potential and kinetic energy of its molecules
what is a monatomic gas
one in which atoms are not bound to each other eg. helium
what is a polyatomic molecule
one which consists of 2 or more atoms
what kind of gases are monatomic
ideal gases
Why do ideal gases have entirely kinetic energy as their internal energy
there are no forces of attraction between the atoms. Ideal gases possess no potential energy.
Use kinetic theory to explain the pressure exerted by a gas on container walls
Molecules collide elastically with the walls of the container. Each collision results in a momentum change of -2mv for the molecule.
A momentum change (by Newton’s second law) implies that a force was exerted on the molecules by the wall and on the wall by the molecules. (according to N’s third law)
The total force on the wall is the sum of the forces exerted by all the colliding molecules.
The pressure on the wall is force per unit area.
Why can we be confident that the volume of a gas is not directly proportional to the celsius temperature?
If it was, then 0 degrees celsius air would have no volume. This clearly does not happen.
