12.2 THE GAS LAWS Chapter 12 Gases

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? P 1 = 2 atm V 1 = 44 mL P 2 = 4 atm V 2 = ? Equation: PV = k If I know what k is for the first situation, I can determine for the second situation.

P 1 V 1 = k (2atm)(44mL)=88atm*mL Because k is constant, it will not change for the second situation. P 2 V 2 = k (4 atm)V 2 =88atm*mL To find V 2 we simply divide. 88/4 = 22mL

Notice if pressure doubles, the volume is ½ its original value P 1 = 2atm V 1 = 44mL P 2 = 4atm V 2 = 22mL

Boyle’s Law Another way of writing Boyle’s Law would be P 1 V 1 = P 2 V 2