Ideal Gas Law - Rocklin Unified School District
Transcript of Ideal Gas Law - Rocklin Unified School District
Ideal Gas Law
Mathematical relationship between pressure, volume, temperature & number of moles of a gas
Rate of Diffusion
• Smaller molecules
diffuse faster than
larger molecules at
the same temperature
– Ex: Which of the
following molecules
will move faster at 298
K?
• Helium or oxygen?
• Chlorine or nitrogen?
Ideal Gases Vs. Real Gas
Ideal Gas- Accurately describes properties of most gases:
Fit all the assumptions of the kinetic molecular theory:
• Molecules far apart
• Collisions are elastic
• Continuous, rapid, random motion
• No forces of attraction between molecules.
Real Gas- a gas that does not behave ideally
Situations when they wouldn’t behave ideally:
• Gases that are at high pressures & low temperatures do not behave ideally
Why not:
• They get too close and move too slow and start to be attracted to each other.
Standard Temperature & Pressure (STP)
• Most experiments with gases are done at STP
• Known by everyone in science to be:– Standard temperature = 0 ºC (273 K)
– Standard pressure = 1 atm
(kind of like normal body temp. is known by everyone without having to say 98.6°F)
Avogadro’s Law
1 mol O2 gas
Volume = 22.4 L
Mass = 32.00 g
1 mol H2 gas
Volume = 22.4 L
Mass = 2.02 g
Avogadro’s Law
• 1 mole of any gas at STP occupies a
volume of 22.4 L
• 1 mole = 22.4 L (conversion factor)
• Same amount of gas = same volume
• The masses will be different!! 1 mole of
O2 has a higher molar mass than 1 mole
of H2, but contains the same number of
particles
Molar Volume Examples
• What volume will 0.068 mol of O2(g) occupy
at STP?
• How many moles of H2 (g) are in 40.6 L of
gas?
0.068 mol
O2
22.4 L
O2 = 1.5 L O2
1 mol O2
40.6 L H2 1 mol H2= 1.81 mol H2
22.4 L H2
Molar Volume Examples
• How much does 0.098 L of SO2 (g) weigh
at STP?
0.098 L SO2 1 mol SO2 64.07 g SO2 = .28
g SO222.4 L SO2 1 mol SO2
(molar mass)
Ideal Gas Law
PV = nRTPressure
(atm)Volume
(liters)# moles
Ideal gas constant
(.0821)
temperature
(Kelvin)
Ideal Gas Constant, “R”
• How did we find the value of R?
1. Solve ideal gas law for R
2. Substitute variables with values from
conditions of STP
R = 0.0821L·atm
mol·K
R =PV
nT
R =
(1 atm)(22.4 L)
= 0.0821
L·atm
(1 mol)(273 K) mol·K
Ideal Gas Law Example 1
• What is the pressure in atm exerted by a
0.5 mol sample of nitrogen gas in a 10 L
container at 298 K?
– Given: V = 10 L Find: P
n = 0.5 mol
R = 0.0821 (L·atm)/(mol·K)
T = 298 K
Ideal Gas Law Example 1– Given: V = 10 L Find: P
n = 0.5 mol
R = 0.0821 (L·atm)/(mol·K)
T = 298 K
– Plan: PV = nRT
P = nRT
V
– Solve: P = (0.5 mol)(0.0821 (L·atm)/(mol·K))(298 K)
10 L
P = 1 atm
Ideal Gas Law Example 2
• What is the volume, in liters, of
0.250 mol of oxygen gas at 20 C
and 0.947 atm?
– Given: P = 0.947 atm Find:V
n = 0.250 mol
R = 0.0821 (L·atm)/(mol·K)
T = 20 C + 273 = 293 K
Ideal Gas Law Example 2• Given: P = 0.947 atm Find: V
n = 0.250 mol
R = 0.0821 (L·atm)/(mol·K)
T = 20 C + 273 = 293 K
• Plan: PV = nRT
V = nRT
P
• Solve:
V = (0.250 mol)(0.0821 (L·atm)/(mol·K))(293 K)
0.947 atm
V = 6.35 L