Ideal gases Assumptions: There are a huge number N of molecules, each of mass m, moving in random directions at various speeds. On average, the molecules are large distances from each other. --> The average separation is much greater than the size
Ideal gas law: PV = nRT (memorize)
P = pressure in Pa = Nm-2
V = volume in m3
n = the number of moles of gas
R = the universal gas constant =8.31 J mol-1 K-1 (given)
T = the absolute (kelvin) temperature
Also useful to know:
Standard temperature and pressure (STP):
1. T = 273 K = 0 0C
2. Pressure = 1 atm = 1.01 x 105 N m-2 (Pa)
Review: What is a mole (mol)?
1 mol = the amount of substance that contains as many
atoms or molecules as there are in 12.00 g of carbon-12
1 mol= the number of grams of a substance numerically equal to the atomic (or molecular) mass
--> The “grams per mol” is called its “molar mass”
Ex 1. What is the mass in grams (g) of 1 mol of He gas?
Ex 2. How many moles are in 0.700 g of He gas?
Ex 4. How many moles are in 12.8 g of oxygen gas?
Note: 1 mol contains Avagadro’s number NA of particles
NA = 6.02 x 1023 particles per mole (given)
= 6.02 x 1023 mol-1
Ex 6. How many molecules are in 12.8 g of oxygen gas?
(molecular mass = 14.0) gas is at a temperature of 40.0 0C
and a pressure of 0.860 atm?
T = _______ K; P = _________ Pa; n = _______moles
Use: P V = n R T
How many liters is this? (1000 L = 1 m3)
The previous example uses pressure of Boyle’s Law:
PV = nRT = constant b/c T is constant
This is like: xy = constant
--> P and V are inversely proportional
Explain Boyle’s law using particle collisions.
This is an example of pressure of Guy Lussac’s Law:
PV = nRT --> V = nRT/P = constant
--> T/P = constant
--> T = constant x P --> T and P are directly proportional
Explain Guy-Lussac’s law using particle collisions:
of 25 0C. What will be its new volume (in liters) when it is at
a new temp of 50. 0C at constant pressure?
Constant P: PV = nRT
--> solve for P = nRT/V = constant
before = after
nRT1/V1 = nRT2/V2
T1/V1 = T2/V2 (n constant)
Make sure T is in kelvins, Then substitute values in:
This is an example of ofCharles’ Law:
PV = nRT --> P = nRT/V = constant
--> T/V = constant
--> T = constant x V --> T and V are directly proportional
Explain Charles’ law using particle collisions. Especially,
how can pressure remain constant when T increases?