1. Charles’ Law

2. Temperature Changes & Matter
Solids & Liquids expand and contract as temperature changes.
Change is usually v. small.
Gases show large volume changes with temperature changes.

3. Jacques Charles Balloonist.
1787 did expts on how volume of gases depends on temperature.

4. How do hot air balloons work?

5. Relationship between V and T
Pressure & amount are constant.
At high temperature, the gas particles move faster and collide with the walls more often.
Pressure is constant, so volume has to increase.

6. Charles’ Law
Tiger Graphic

7. Data for Volume-Temperature
Trial
Temperature (C)
Volume (mL) 1 10
100 2 50
114 3
132 4
200
167 5
300
202

8. What did Charles do next?

9. Linear Relationship Plot Volume vs. C and you get a straight line.
The relationship between Volume and C is linear.
The equation of a line is: Y = mX + b.

10. Charles extrapolated the graph to 0 volume.
At 0 mL, the X-intercept is -273 C.

11. Hints of Kelvin scale
Charles extrapolated his data to see the temperature at which the volume was 0.
1st indication that the temperature -273 C might have a fundamental meaning.
Why did Charles have to extrapolate his lines in this temperature range instead of taking data?

12. Plot Volume vs. Kelvin Temp.
Get a straight line that passes through the origin.
The relationship between the variables is direct and proportional.
Y = mX or Y/X = m.

13. Charles’ Law: Verbal
The volume of a gas at constant pressure varies directly with its absolute (Kelvin) temperature.

14. Charles’ Law: Graphically
Plot Volume vs. Kelvin Temperature
Straight line that passes through the origin.
V = kT or V = k T

15. Compare Charles’ & Boyle’s Laws
Charles’ Law:
V = kT or V/T = k.
Direct relationship: linear & passes through origin
Boyle’s Law: PV = k
Inverse relationship. hyperbola

16. Charles’ Law: Problems
V1 = V2 T1 T2
Given any 3 variables, you can find the 4th.

17. The low temperature region is always extrapolated. Why?

18. Gay-Lussac’s Law
Pressure &
Temperature

19. Typical data from a Gay-Lussac type experiment
Typical data from a Gay-Lussac type experiment. What kind of relationship is illustrated in this graph?
T (K)

20. Gay-Lussac’s Law
Describes relationship between pressure & temperature at constant volume & amount.
P = kT or P/T = k
What kind of relationship is this?
Straight line with y-intercept of zero. It’s direct.

21. Gay-Lussac: Verbal
The pressure exerted by a confined gas is directly related to the Kelvin temperature at constant volume.

22. Gay-Lussac’s Law
P1 = P2
T T2
Useful problem-solving format.

23. Gay-Lussac Examined relationship betw P & T at constant V and moles
If T , the gas molecules will move faster, colliding with the walls more frequently & more energetically.
Pressure results from collisions between gas molecules & walls of container. So, if T , we expect P .