Ideal Gases Flashcards
Combined Gas Law
Gay-Lussac’s, Boyle’s, and Charles’ Law can be combined into a single equation:
P1V1/T1 = P2V2/T2
The product of the pressure and volume of a gas divided by its absolute temperature is a constant as long as the amount of gas is kept constant
What happens when we change the amount of gas?
Consider: 1 mol of gas at a constant T in a container with a movable top (constant P)
add 2 mol of gas into the container
V and n are directly proportional when T and P remain constant!
n = 1 mol, V = 1L
n = 3mol, V = 3L
Avogadro’s Law
Changing amount of gas
V/n = constant
From last lesson, we know that this type of relationship means:
V1/n1 = V2n2
the volume of gas is held constant. The pressure of a gas is directly proportional to its temperature while the volume is kept constant.
The Ideal Gas Law
Combining Gay-Lussac’s, Boyle’s, Charles’, and Avogadro’s Law gives us the following result:
PV/nT = constant
This constant has a symbol (R) and is called the universal gas constant
PV=nRt
INDEAL GAS LAW
What is the value of R?
When pressure is measured in kilopascals (kPa), volume in Liters, and the amount of a gas in moles, the value of R is,
8.314 Kpa x L x mol-1 x K-1
What is Ideal referring to?
An ideal gas has the following characteristics:
Its entities all have high translational energy, moving randomly in all directions in straight lines
When its entities collide with each other or with the container walls, the collisions are perfectly elastic (no loss in kinetic energy)
The volume of an ideal gas entity is insignificant (zero) compared to the volume of the container
There are no attractive or repulsive forces between ideal gas entities
Ideal gases do not condense into liquids when cooled
There is no such thing as an ideal gas!
The ideal is an imaginary standard to which the behaviour of a known gas is compared
It is simply a convenient approximation – or model – that works very well as we try to predict the behaviour of gases
At ordinary conditions, most gases obey the gas laws fairly well and their behaviour resembles that of an ideal gas
Can we always use Ideal Gas Law?
Gases behave most ideally at low pressures and high temperatures
When the pressure gets too high, attractive forces between entities become significant (can’t have those for an ideal gas!)
When the temperature gets too low, the entities move too slowly and again attractive forces become significant
So we need to be careful about using ideal gas law at high pressures and/or low temperatures
Molar Volume: A consequence of Ideal Gas Law
Thus, at STP, one mole of ANY ideal gas occupies 22.4 L of volume!!
Note: At SATP, the molar volume of an ideal gas is 24.8 L.
Molar mass
Mas per 1 mole of the gas
molar mass does not change with temperature bc the mass of any substance is not affected by temperature or pressure.
Molar volume
Space occupied by 1 mole of the gas
Volume does change with temperature. The space a gas occupies is affected by temperature + pressure.
