Gases Flashcards
Absolute 0, and degrees kelvin conversions.
On the thermodynamic (Kelvin) temperature scale, absolute zero is defined as:
The lowest temperature possible. Equal to 0 K or -273.15 °C
Kelvin to degrees is -273.
Absolute zero is defined s as:
The temperature at which the molecules in a substance have zero kinetic energy.
This means for a system at 0 K, it is not possible to remove any more energy from it.
According to ideal gas laws, absolute 0 is the temperature at which the pressure or volume of a gas is extrapolated to 0.
What is Charles law?
V ∝ T
This means the volume is directly proportional to the temperature of a gas
V1/T1 = V2/T2
What is Boyles law?
If the temperature T of an ideal gas is constant, then Boyle’s Law is given by:
Pressure is inversely proportional to the volume of a gas
P1V1 = P2V2
PV = constant
What is the pressure law?
Pressure Law
If the volume V of an ideal gas is constant, the Pressure law is given by:
P ∝ T
This means the pressure is proportional to the temperature
P1/T1 = P2/T2
Define pressure
pressure is the force per unit area
P= F/A
What happens to gas molecules during collisions?
Gas molecules move about at random speeds, and when they collide with each other or with the walls of the container they are held in, they exert a force, since force is the rate of change of momentum.
What is a ideal gas?
An ideal gas is one that obeys the relation:
pV ∝ T
An ideal gas obeys Boyles law.
What is the ideal gas equation?
Pv/T = constant where T is temperature in kelvin.
The constant here is nR where n is number of mols and R is the molar gas constant 8.31.
The constant can also ne NK where N is the number of molecules, and K is the Boltzmann’s constant 1.38x10^-23.
So, the ideal gas equation can be written as pV=NKT or pV =nRt
Work done by gases
When a gas expands, it does work on its surroundings by exerting pressure on the walls of its container
The work done when a volume of gas changes at constant pressure is defined as:
W = pΔV
What is Avogadros constant?
Avogadro’s constant (NA) is defined as:
The number of atoms of carbon-12 in 12 g of carbon-12; equal to 6.02 × 10^23 mol-1
How many atoms are theres in 3 mols of Carbon?
3 x 6.02x10^23
What is a mole?
One mole of any element is equal to the relative atomic mass of that element in grams
For example, helium has an atomic mass of 4, meaning 1 mole of helium has a mass of 4 g
If the substance is a compound, add up the relative atomic masses, for example, water (H2O) is made up of
2 hydrogen atoms (each with an atomic mass of 1) and 1 oxygen atom (atomic mass of 16)
So, 1 mole of water would have a mass of (2 × 1) + 16 = 18 g
How many mols are in 24g of C-12?
The nucleon number is 12. 24/12 = 2. So there are 2 mols.
What is molar mass?
The molar mass of a substance is the mass, in grams, in one mole
Its unit is g mol-1
The number of moles from this can be calculated using the equation:
Mr x mols = mass.
Mr is the molar mass.
Mr mols had a mass on his head.
What is different about the internal energy of an object compared to a gas?
ideal gas molecules are assumed to have no intermolecular forces
This means they have no potential energy, only kinetic energy
So the ideal gas internal energy is the sum of all the kinetic energies of the atoms
In equation form, this can be written as:
U =N x Ek
Where:
U is the internal energy of the ideal gas in joules, J
N is the number of particles in the ideal gas
Ek is the average kinetic energy of a single particle in joules, J
