Chapter 10 - Properties Of Gases Flashcards
Charles’ Law
The volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature (Kelvin Scale)
V/T is a constant
Boyle’s Law
When a fixed mass of gas is kept at constant temperature its volume is inversely proportional to its pressure
P1V1 =P2V2
Gay-Lussac’s Law of combining Volumes
In a reaction between gases the volumes of the reacting gasses and the volumes any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temperature and pressure
Avogadro’s law
Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure
What is an ideal gas?
An ideal gas is one which obeys all the gas laws (assumptions of the kinetic theory of gases)
at all temperatures and all pressures
What are the assumptions of the kinetic theory of gases? (x5)
1) Gases are particles that are in continuous motion, colliding with each other and with the walls of the container.
2) There are no attractive or repulsive forces between the molecules of a gas
3) The gas molecules are so small and so widely separated that the actual volume of all the molecules is negligible compared with the space that they occupy
4) When molecules collide ,the collisions are perfectly elastic…no loss of kinetic energy
5) The average kinetic energy of the molecules in a sample of gas is proportional to the absolute temperature (K)
What are the Limitations of the kinetic theory of gases? 3 Reasons this theory is not true.
1) Forces exist - some gases are polar - NH3. Also, there are weak Van der Waal forces between non-polar gases - Cl2
2) Under high pressure gas molecules are much closer together so their volume is NOT negligible compared to the distance between them.
3) The collisions between the molecules are NOT perfectly elastic.
Is there such a thing as an ‘Ideal Gas’???
No.
Real gases DEVIATE from ideal behaviour because:
1) They liquify at LOW temperature
2) They liquify at HIGH pressure
( think of the steam from a kettle hitting a cold window )
Reasons:
i) The force of attraction between the gaseous molecules is not taken into account.
ii) The volume occupied by the gaseous molecules is not taken into account.
iii) Their collisions are not perfectly elastic.
Under what conditions do real gases come CLOSEST to ideal behaviour?
At HIGH TEMPERATURE and LOW PRESSURE
Relative Atomic Mass
The average mass of one atom of an element compared to 1/12th the mass of the carbon-12 isotope.
Relative molecular mass
The average mass of one molecule compared to 1/12 the mass of the carbon-12 isotope
