Accelerated Chemistry
Chapter 11 Part 2 – The Ideal Gas Law
Chapter 11 problems - Part 2: page 390 Chapter Review: 40, 41, 42, 44, 45, 48, 52, 58, 63, 68, 69, 70, 71, 73
11.3 The Ideal Gas Law– A new formula that can help us solve all kinds of gas law problems more easily.
Ex1: Calculate the volume of 1.00 mole of Hydrogen at 20.0 C0 and 1000.0 torr.
There are two ways that we can solve the above problem:
Po Tn Vo = Pn To Vn
or
PV = nRT
P is
V is
n is
R is the
T is
In general,
PTV = PTV is used for problems containing
PV = nRT is used for problems:
containing set of conditions,
solving for ,
solving for ,
calculating
calculating , and
involving .
Stoichiometry of Gases –
For problems at STP, there is nothing new here. But, when chemistry happens at conditions that are not standard, we must adjust our thinking, because .
Let’s review reaction stoichiometry.
Note: a “stoich” problem can be recognized by the fact that information from one
substances is and the problem is asking for information about a
substance.
Ex2: How many L of Oxygen are needed to react with 50.0 L of Hydrogen at STP?
Hey! Avogadro’s principle also works for nonstandard conditions:
Ex3: How many L of Oxygen are needed to react with 50.0 L of Hydrogen at 100.0 torr
and 873 K?
BUT, gases do not behave ideally at low temperature and high pressure, i.e. non-STP conditions.
So when the the conditions are non-STP values, 22.4 L can’t be used. So, use PV=nRT and solve for V (assume one mole).
PV = nRT
Plug this value into the appropriate steps of the stoichiometry problem.
Ex4: Find the number of liters of Oxygen that are generated when 50.0 grams of sodium
chlorate is decomposed at 0.950 atm and 20.0 C0.
Ex5: If 555.0 L of carbon dioxide are generated by a lawn mower engine on a lovely
Sunday afternoon (757.0 torr and 37.00 C0 - well it is kind of hot today...), how
many grams of octane were consumed?
It is also possible to do Density problems.....
Ex6: Find the density of carbon dioxide at STP.
Ex7: Find the density of carbon dioxide at 546.0 K and 4.00 atm.
It is also possible to do molecular weight (molar mass) of a gas problems …
Ex8: If 18.0 grams of a gas at 380 torr and 546.0 K occupies 44.8 L, what is the molecular
weight of the gas?
Really fun problems....
Ex9: What is the density of the carbon dioxide produced if 50.0 mL of ethyl alcohol
(C2H5OH) is combusted in a 1000.0 mL volumetric flask at 25.0 C0 and
101.1 kPa? The density of the alcohol is 0.791 g/mL.
Deviation From Ideal Behavior
Real gases:
- behave according to the KTG - why you may ask?
1. Real gases have molecules that
2. Real gases have
Ideal gases:
- a gas that to the KTG
-
- gases only behave close to ideally at pressures and temperatures.
- At low temperatures and high pressures, gases greatly from ideal
behavior.
There is an equation that enables us to account for deviations in behavior - it
contains correction factors that are specific for a gas - Van der Walls equation –
you’ll see it in 2 years in AP Chemistry
Some gases are close to ideal:
- they are small and nonpolar
- H2, He, Ne
- O2 and N2 are not too bad
- NH3, H2O are not even close to ideal
We see gases react in Reaction Stoichiometry, how does this happen if they are in the same physical state?
Gases react if and only if their particles ______with one another. This is true for real gases because we saw that ideal gases have elastic collisions.
11 Part 2 Notes - S.doc Page 8 of 8