Chapter 13.1 & 14.1, 14.2, 14.3 –

Gases – Tutorial               Std 4


Kinetic Molecular Theory

   a. gas particles do not repel each other

   b. gas particles are 1000’s of times small than distances between them.

   c. gas particles in constant, random motion

   d. no energy lost when particles collide with each other or their container

   e. all gas particles at the same temp. have ≈ same energy


Real vs ideal gases

1. Ideal gas:

a. gas particles take up no space

b. there are no intermolecular forces

c. follows the gas laws under all temperature and pressure conditions.

2. There is no ideal gas, you can only get close. Gases behave most like “ideal” at LOWER pressures and HIGHER temperatures.  Both of these conditions reduce the effect of gas particles on each other  =>  more ideal.


   molar volume means – 1mole of any gas at STP = 22.4 L





When to use which gas law:

a. Gas Law to use when partial pressures of 2 or more gases are being calculated:


         Dalton’s Law of Partial Pressures     Ptotal = P1 + P2 + P3 + . . .


b. Gas Laws to use when any condition (s) change (s):

   Units of measure for P & V must be the same for conditions 1 and 2.


1. Boyle’s Law       P1 V1  =  P2 V2    (inversely proportional)


2. Charles’s Law   


3. Gay-Lussac’s Law       (temp must always be K)


4. Avogadro’s law in gases:    =


4. Combined gas law      (combines Boyle, Charles & Gay-Lussac) – This allows you to do all of the types of gas laws involving changes in conditions!!!!


c. Gas Law to use for problems with no change in conditions

The Ideal Gas Law 


PV = nRT       the constant R depends on units of measure used for variables. 

R = 0.0821   (these are the most common units used)


Units of measure must always be:  L, atm, mol, & K



Unit Conversions used for gas law calculations:


         1 atm = 760 mmHG = 760 Torr = 101.3 kPa = 101,325 Pa = 14.7 psi


         1000mL = 1 L


         n  is used to represent moles in gas law equations


         All gas law formulas require temperature to be in Kelvin

                °C + 273 = K