Kinetic Theory of Gases
1. Made of tiny particles.
2. Relatively large distances between particles.
3. Particles in constant motion with KE = 1/2 ms2.
4. Make perfect elastic collisions.
5. KE directly proportional to T.
6. Particles of different mass at same T have same average KE.
Pressure is force applied per unit area. In the SI System pressure is
measured in
pascals = Pa = kg m-1s-2. The air surrounding
the earth exerts an average pressure of 1 atmosphere = 101.3 k Pa = 760
mmHg(torr) = 14.7 lb/in2.
Boyle's Law - Temperature constant, the volume of an ideal gas is inversely proportional to the pressure on the gas.
(P)(V) = constant; P1 = V2
P2 V1
Charles's Law - Pressure constant the volume of an ideal gas is directly
proportional to the Kelvin temperature.
V = constant; T1 = V1
T
T2 V2
Combined Gas Laws
(P1)(V1) = (P2)(V2)
T1
T2
Standard temp. & press., STP = 0oC (273 K) and 1 atm (760 torr)
One mol. of any ideal gas at STP contains 6.02 x 1023 formula
units,
weighs one molar mass and occupies 22.4 L.
For example, at STP:
32.0 g O2 occupies 22.4 L and 2.02 g H2 occupies
22.4 L
and 28.0 g CO occupies 22.4 L and 20.2 g Ne occupies 22.4 L.
3 H2
+ N2
<===> 2 NH3
3 molecules 1 molecule
2 molecules
6.0 amu
28 amu
34 amu
3 moles
1 mole
2 moles
6.0 g
28 g
34 g
3(22.4L)
22.4 L
2(22.4L)
Calculate the volume of NH3 measured at STP, and at 25oC
and 680 torr,
produced from 0.77 g H2 and excess N2.
0.77g H2 x 1 mol H2x 2 mol NH3
x 22.4 L NH3 = 5.69 = 5.7 L NH3
2.02g H2 3 mol H2
1 mol NH3
(P1)(V1) = (P2)(V2); V2 = (P1)(V1)( T2)
T(1)
T(2)
T(1) P(2)
V2 = (760 torr)(5.692L) x 298 = 6.9 L
(273 K )(680 torr)
An alternate approach is:
0.77 g H2 x 1 mol H2 x 2 mol
NH3x 22.4 L NH3 x 22.4 L NH3 x
293
K x 760 torr = 6.9L
1
2.02 g H2 3 mol H2
1 mol NH3 1 mol NH3
273 K 680 torr