1. Atmospheric Pressure
Pressure is equal to a force per area. The gases in the air exert a pressure called atmospheric pressure.
Atmospheric pressure is a result of all of the collisions that result from air particles bumping into things as they move around.
Atmospheric pressure is measured with a barometer.

2. Units for Pressure mmHg (millimeters mercury) or torr
1.000 atm = mmHg = torr
1.000 atm = 101,325 pascal (Pa)
1.000 atm = pounds per square inch (psi) SI
UNIT!
USED IN ENGINEERING!

3. Inverse and Direct ProportionsB

4. Inversely Proportional Ex: Boyle’s Law (V as a function of P)
P (torr)
V (mL)
100
4560
200
2280
300
1520
400
1140
500
912
600
760
700
651
800
570
900
507
1000
456
1100
414
1200
380
1300
351
1400
326
1500
304

5. Boyle’s Law at Different Temperatures (P as a function of V)

6. INVERSE PROPORTIONS As one variable goes up, the other goes down!
Produces a
curved graph…
Multiplying the two variables equals a constant. P V T
constant
P1V1 = P2V2

7. Directly Proportional Ex: Charles’ Law (V as a function of T)
T (K)
V (mL) 50
100
200
150
300
400
250
500
600
350
700
800
450
900
1000
550
1100
1200
650
1300
1400

8. DIRECT PROPORTIONS T As one variable goes up, so does the other! V
Produces a straight
line graph…
Dividing the one variable
by the other
equals a constant.
V1 V2
T T2 =

9. Want Practice?:
T (K)
P (atm) 50
100
150
200
250
300
3.0
350
400
450
500
550
600
650
700
Complete the following data table for Gay Lussac’s Law (Volume is constant)
Graph your data (properly).
Are P & T inversely or directly related? Why?