1. The Gas Laws
Chapter 14.1

2. Gas Laws
Our current understanding of the nature of gases is based on the work a many scientists over many years.
Boyle
Charles
Gay-Lussac

3. Kinetic Molecular Theory – describes the behavior of gases in terms of particles in motion
gas particles are relatively far apart
the volume of the particles in a gas is small compared to the empty space around the particles
gases are compressible
gas
liquid
solid

4. Kinetic Molecular Theory
since gas particles are far apart, gas particles do NOT attract or repel each other
gas particles are in constant random motion
collisions between gas particles are elastic (no kinetic energy is lost when gas particles collide at the same temperature)

5. Kinetic Molecular Theory
all particles of gas have the same average kinetic energy at the same temperature
if the temperature increases, so will the KE (the particles will move faster)
if the temperature decreases, so will the KE (the particles will move slower)

6. Factors Affecting Gas Behavior
the number of particles (amount)
temperature
pressure
volume
These factors are interdependent. If one changes, it will affect one or more other factors.

7. Vocabulary Word Pressure: force per unit area Units of pressure
kilopascal (kPa)
mm Hg
torr
psi
atmosphere (atm)

8. Instruments used to measure pressure
barometer: used to measure air or atmospheric pressure

9. Instruments used to measure pressure
manometer: used to measure gas pressure in a closed container

10. Volume If you squeeze a closed balloon, the volume decreases
the number of particles remains the same
the temperature remains the same
the pressure increases (the particles are closer together, so they collide more frequently)

11. Volume When you release the balloon, the volume increases
so the pressure decreases

12. Boyle’s Law
Robert Boyle ( ) was an Irish chemist that studied the effects of volume and pressure on gases in a closed cylinder.

13. Boyle’s Law
He showed that at constant temperature doubling the pressure (from 2 atm to 4 atm) would decrease the volume by 1/2 (from 5 L to 2.5 L).

14. Boyle’s Law
He also showed that at constant temperature decreasing the pressure by half (from 2 atm to 1 atm) would increase the volume by 2 fold (from 5 L to 10 L).

15. Boyle’s Law
Boyle concluded that volume and pressure are inversely related
Since the product of pressure and volume at any point on the line = 10 atm•L
P1V1 = P2V2

16. Vocabulary Word
Boyle’s Law: P1V1 = P2V2 the volume of a gas varies inversely with pressure (at a constant temperature).

17. Using Boyle’s Law
Air in a cylinder occupies mL at 1.08 atmospheres (atm) of pressure. If the pressure increased to 1.43 atm, what would the new volume be?
P1V1 = P2V2
(1.08)(145.7) = (1.43)(V2)
= mL
1.43

19. Jacques Charles
Jacques Charles ( ) studied the relationship btwn volume and temperature at constant pressure.
He found that as temperature increased, so did pressure.

20. Jacques Charles
As temperature increases the gas particles move faster.
This increases the number of collisions.
In order to maintain the same pressure, gas particles must spread out.
This increases the volume.

21. Jacques Charles Temperature and pressure are directly proportional.
The graph predicts where the volume should equal 0 (lowest theoretical temperature),
oC or 0 K.

22. Charles’ Law
V1 = V2
T T2
Note: temperature must be in degrees Kelvin

23. Vocabulary Word
Charles’ Law: states that the volume of a given mass of gas is directly proportional to its kelvin temperature at constant pressure
V1 = V2
T T2
To convert btwn Celsius and Kelvin:
Tk = Tc + 273

24. Charles’ Law Using Charles’ Law in calculations:
a gas at 89oC has a volume of 0.67L. If the volume increases to 1.12L, what is the temperature?
V1 = 0.67 L V2 = 1.12 L
T1 = = T2 = ?

25. Charles’ Law V1 = 0.67 L V2 = 1.12 L T1 = 89 + 273 = 362 T2 = ?
0.67 = 1.12
362 T2
(0.67) T2 = (1.12) (362)

26. Charles’ Law (0.67) T2 = (1.12) (362) T2 = (1.12) (362) 0.67 = 605 K
= = 330oC

27. Joseph Gay-Lussac
Joseph Gay-Lussac explored the relationship btwn temperature and pressure at constant volume.
He found that it was a directly proportional relationship.

28. Vocabulary Word
Gay-Lussac’s law: states that the pressure of a given mass of gas varies directly with the kelvin temperature when the volume remains constant
P1 = P2
T T2

29. Gay-Lussac’s Law using Gay-Lussac’s law in calculations
The pressure in a tire is 1.88 atm at 25oC. If the temperature increases to 37oC, what will the pressure be?
P1 = P = P2
T T

30. Gay-Lussac’s Law 1.88 = P2 298 310 (1.88) (310) = (298) P2
(1.88) (310) = (298) P2
(1.88) (310) = P2
(298)
1.96 atm = P2