Gases Flashcards
what does the kinetic-molecular theory describe?
it is a model for describing the behaviour of gases, based on specific assumptions of ideal gases
describe the ideal gas model:
1) no volume
2) constant and random motion, all collisions are elastic
3) no intermolecular forces
4) average kinetic energy of the molecules is directly proportional to the absolute temperature
what is pressure of gases caused by?
molecules striking the walls and each other
what is zero degrees Celsius in Kelvins?
273.15K
what is the SI unit for pressure?
pascal, P (N/m^2)
101.3kPa is also equal to:
760 mmHg=760 torr=1 atm
Standard Temperature and Pressure (STP)
temperature = 273.15K and pressure = 1 atm
what is the equation for the Ideal gas law?
PV=nRT
universal gas constant R
0.0821 L atm/ K mol
Charles’s Law
if the pressure is constant, the volume is proportional to the temperature. thus the gas will expand when heated and contract when cooled
Boyle’s Law
if the temperature is constant, pressure is inversely proportional to volume
if the volume is constant, pressure is ______ to temperature
proportional
when does the combined gas law apply?
when n (the amount of gas) stays constant
Avogadro’s law
equal volumes of different gases at the same temperature and pressure contain the same number of particles
standard molar volume
the volume that one mole of any gas (ideal gas) occupies at STP
what is the standard molar volume?
22.4 L
under what conditions do the laws of ideal gases deviate from behaviour of real gases?
low temperatures and high pressures
describe the deviations of real gases from ideal gas behaviour
- intermolecular forces causes pressure to decrease
- particles have volume so that the free space available decreases (V real decreases) unless very high pressure which causes V to increase due to repulsions
van der Waals equation
accounts for differences in the observed behaviour of real gases and calculated properties of ideal gases
what are the two constants in the van der Waals equation and what do they depend on?
a= intermolecular force of the gas
b=weight/size of the gas
partial pressure
in a mixture of gases, the pressure that just one gas exerts
Dalton’s law of partial pressures
the total pressure is simply the sum of the partial pressures of all the constituent gases
effusion
the escape of a gas molecule through a very tiny hole that is comparable in size to the molecules themselves into an evacuated region
in an effusion experiment, what does the rate of gas effusion depend on?
how fast the molecules move, which in turn depend on speed (kinetic energy is the same due to temperature, but speed is not the same, depend on mass of gas)
Graham’s law of effusion
ratio of rate of effusion of gas A over B is equal to the square root of molar mass of B over molar mass of A
for one gas, what is the trend of average speed as the temperature increases?
average speed increases due to increased kinetic energy
