Chapter 12
Gases
12.2
THE GAS LAWS
Review
 What are 3 properties that all gases share?
 Explain kinetic- molecular theory.
 Define pressure and what are the SI units?
Measurable Properties of Gases
 All gases have the following measurable properties:

(P) = Pressure

T = temperature (K)

V = total volume

n = number of moles of the gas
Pressure – Volume Relationships
 Think back to the syringe filled with air.
 As I pushed down on the plunger, what increased?
 What decreased?
 As pressure increases, volume decreases
 Or just the opposite : As volume increases, pressure
decreases
 As the volume of a container increases, the gas
particles have more room to move around
 This leads to less collisions and therefore, less
pressure
Boyle’s Law
 For a given gas in a specified space, the amount of
pressure times the volume will always be the same
PV = k
Where:
P=Pressure
V=Volume
K=constant (doesn’t change)
Example
 If I know the pressure in my syringe is 2 atm and the
volume is 44mL, what happens to the volume if I
double the pressure?
What is given?
 Equation:
 P1 = 2 atm
 V1 = 44 mL
PV = k
 P2 = 4 atm
 V2 = ?
If I know what k is for the
first situation, I can
determine for the second
situation.
 P1 V 1 = k
 P2 V 2 = k
(2atm)(44mL)=88atm*mL
(4 atm)V2 =88atm*mL
 Because k is constant, it
To find V2 we simply
divide.
will not change for the
second situation.
88/4 = 22mL
 Notice if pressure
doubles, the volume is ½
its original value
P1 = 2atm
V1 = 44mL
P2 = 4atm
V2 = 22mL
Boyle’s Law
 Another way of writing Boyle’s Law would be
P1V1 = P2V2