Intro to Gases
HW = Read 13.2, #’s
10,12,15,16,18,22
Atmospheric Pressure
The gases in the air are exerting a pressure
called atmospheric pressure
Atmospheric pressure is a
result of the fact that air has
mass and is attracted by
gravity producing a force.
Atmospheric pressure is
measured with a barometer.
Units for Pressure
• mmHg (millimeters mercury) or torr
• 1.000 atm = 760.0 mmHg = 760.0 torr
• 1.000 atm = 101,325 pascal (Pa)
SI
UNIT!
• 1.000 atm = 14.69 pounds per square inch (psi)
USED IN
ENGINEERING!
Gases can be described using the
following four variables:
V = volume of the gas (liters, L)
P = pressure (atmospheres, atm)
T = temperature (Kelvin, K)
n = amount (moles, mol)
Temperature and Volume
Charles’ Law
(V as a function of T)
T (K)
V (mL)
0
0
50
100
100
200
150
300
200
400
250
500
1200
300
600
1000
350
700
400
800
450
900
600
500
1000
400
550
1100
600
1200
650
1300
700
1400
Directly Proportional
1600
Volume (mL)
1400
800
200
0
0
200
400
Temperature (K)
600
800
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
1500
1100
414
1000
1200
380
500
1300
351
0
1400
326
1500
304
Inversely Proportional
5000
4500
Volume (mL)
4000
3500
3000
2500
2000
0
200
400
600
800
1000
Pressure (torr)
1200
1400
1600
Inverse and Direct
Proportions
Directly
Proportional
Inversely Proportional
Boyle’s Law at Different Temperatures
(P as a function of V)
INVERSE PROPORTIONS
• As one variable goes up, the other goes
P
down!
T
constant
V
• Produces a
curved graph…
• Multiplying the two variables equals a
constant.
P1V1 = P2V2
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
T1
=
V2
T2
P1 x V1 = P2 x V2
P may change and V may change,
but their product stays the same!
What stays constant in this
scenario?