CHM 108Suroviec

Spring 2014

Chapter 51

I. Pressure

A. Molecular collisions

Pressure = ForceArea

(force = mass x acceleration)

2

I. Pressure

B. Pressure Units

Barometer

3

II. Gas Laws

A sample of gas has 4 physical properties that are interrelated.

4

A. Boyle’s Law

Relationship between pressure and volume at constant T and n.

5

A. Boyle’s Law

If you were to go SCUBA diving, your lunch capacity is a constant. So if you moved from the bottom at 3 atm to the surface at 1 atm with out breathing, what happens to the volume of the air in your lungs?

6

B. Charles’ Law

At constant pressure and moles, volume decreases with decreasing temperature.

7

B. Charles’ Law

Given a balloon that has 3.20L to start off at room temperature (25oC) and is submerged into liquid N2 the volume shrinks down to 0.816L what is the temperature of liquid N2?

8

C. Avogadro’s Law

Relationship between volume and number of moles and constant T and P

9

C. Avogadro’s Law

A 3.86 L container contains 0.252 moles of gas . How many moles of the same gas would be required to fill a 8.50L container?

10

II. Ideal gas law

Knowing each of these individual gas laws allows us to make a law that covers all ideal gas situations.

11

II. Ideal gas law

1. What is the volume of 8.24 g of CO2 (g) at STP?

2. Argon light bulbs have a pressure of 1.20 atm and are at a temperature of 18oC. When they are turned on they heat to a temperature of 85oC. What is the new pressure at this temperature?

12

III. Using the ideal gas law

A. Density One mole of an ideal gas occupies 22.4L Density of a gas is directly proportional to molar mass

13

A. Density

Determine the M and molecular formula of an unknown compound that contains Fe and O

14

B. Gas stoichiometry

Stoichiometry for gas reactions is the same if it were a liquid or a solid. Use the balanced chemical equation.

Amount of reactant moles of reactant moles of product amount of product

What is the volume of CO2 produced at 37oC and 1.00atm when 5.60g of glucose is reacted in the following reaction:

C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(l)

15

III. Mixture of Gases & Partial Pressure

Partial pressure = Pressure of individual gas components in a mixture

Dalton’s Law = total pressure of a mixture of gasses is just sum of the pressure each gas would exert individually

Mole fraction = dimensionless quantity that expresses the ratio of the number of moles in 1 component to the number of moles in all the components

16

A. Partial Pressures

V and T are constant

P1 P2 Ptotal = P1 + P2

17

A. Partial Pressures

Knowing:

Ptotal = P1 + P2 PV = nRT

18

A. Partial Pressures

A sample of natural gas contains 8.24 moles of CH4, 0.421 moles of C2H6, and 0.116 moles of C3H8. If the total pressure of the gases is 1.37 atm, what is the partial pressure of propane (C3H8)?

19

IV. Kinetic molecular Theory

Gas laws help predict behaviors of gasses, but they do not explain what is happening at the molecular level.

We know that hot air rises and can predict the results (Charles’ Law), but why does it do that?

20

A. Kinetic Molecular Theory

1. A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions. The molecules can be considered to be points; that is, they possess mass but have negligible volume.

2. Gas molecules are in constant motion in random directions, and they frequently collide with one another. Collisions among molecules are perfectly elastic.

1. Gas molecules exert neither attractive nor repulsive forces on one another.

4. The average kinetic energy of the molecules is proportional to the temperature of the gas in Kelvins. Any two gases at the same temperature will have the same average kinetic energy

21

B. Velocity of gases

Using what we know of the gas laws and using these postulates we can see why gases behave the way they do.

22

KE= ½ mu2

B. Velocity of gases23

The distribution of speedsof three different gasesat the same temperature

B. Temperature effects

Average kinetic energy is proportional to temperature.

24

B. Temperature effects25

The distribution of speedsfor nitrogen gas moleculesat three different temperatures

B. Using the Kinetic Molecular Theory

Calculate the urms for O2 and Ar at 298K. Which has the faster moving gas molecules?

26