1. Chapter 11 Gases

2. Gases: What Are They Like?
Composed of widely separated particles in constant, random motion
Flow readily and occupy the entire volume of their container
Vapor is the term used to denote the gaseous state of a substance existing more commonly as a liquid
e.g., water is a vapor, oxygen is a gas
EOS
Many low molar mass molecular compounds are gases – methane (CH4), carbon monoxide (CO)
Chapter 5: Gases

3. Kinetic-Molecular Theory
Provides a model for gases at the microscopic level
Molecules move in straight lines until they contact something else
Temperature is the average kinetic energy of the Particles
EOS
Chapter 5: Gases

4. Kinetic Moleccular Theory
A gas consists of a collection of small particles traveling in straight-line motion and obeying Newton's Laws.
The molecules in a gas occupy no volume (that is, they are points).
Collisions between molecules are perfectly elastic (that is, no energy is gained or lost during the collision).
There are no attractive or repulsive forces between the molecules.
The average kinetic energy of a molecule in all gases is the same

5. Molecular Diffusion
Diffusion is the process by which one substance mixes with one or more other substances as a result of the translational motion of molecules
EOS
Chapter 5: Gases

6. Effusion
Effusion is the process in which a gas escapes from its container through a tiny hole, or orifice
EOS
Chapter 5: Gases

7. Gas Pressure
Pressure is the force per unit area – consider the unit pounds per square inch
SI units express pressure in Newtons (N) per square meters (m2) -- or N m–2
a.k.a. – Pascals (Pa)
EOS
A barometer is an instrument used to measure atmospheric pressure
Chapter 5: Gases

8. Barometers Used to measure atmospheric pressure
The pressure exerted by a column of mercury exactly 760 mm high is defined as 1 atmosphere (atm)
EOS
Gases tend to settle under the effects of gravity – pressure  as altitude 
Chapter 5: Gases

9. Examples of Pressure Units
Given these values, one can generate conversion factors to switch between units:
e.g., 760 mmHg = bar
EOS
Chapter 5: Gases

10. Molar Volumes and Standard Pressure and Temperature
Standard Temperature and Pressure (STP) is defined as
T = 0 oC and P = 101.3kPa
EOS
The molar volume of a gas is the volume occupied by one mole of the gas at STP= 22.4 L/mol
Chapter 5: Gases

11. Molar Volumes and Standard Ambient Pressure and Temperature
Standard AmbientTemperature and Pressure (SATP) is defined as
T = 25 oC and P = 100kPa
24.8
EOS
The molar volume of a gas is the volume occupied by one mole of the gas at SATP= 24.8 L/mol
Chapter 5: Gases

12. Temperature-Volume Relationship: Charles’s Law
The volume of a fixed amount of a gas at constant pressure is directly proportional to its Kelvin temperature
i.e., if V , then T 
or V/T = k
EOS
Chapter 5: Gases

13. Temperature-Volume Relationship: Charles’s Law
Absolute zero is the temperature obtained by extrapolation to zero volume
EOS
Absolute zero on the Kelvin scale = – °C
and ...
K = 0 °C
Chapter 5: Gases

14. Pressure-Volume Relationship: Boyle’s Law
For a given amount of a gas at constant temperature, the volume of the gas varies inversely with its pressure
i.e., if V , then P 
EOS
Chapter 5: Gases

15. Pressure-Volume Relationship Boyle’s Law
EOS
or V = k*1/P
P1V1=P 2V2
For a given amount of a gas at constant temperature, the product of the pressure and the volume is a constant
PV = k
Chapter 5: Gases

16. Pressure- temperatureRelationship Gay-Lussac’s Law
EOS /
For a given amount of a gas at constant volume, the pressure of a gas is proportional to its temperature
Chapter 5: Gases

17. For initial and final conditions:
The Combined Gas Law
Given the various gas laws, all can be combined into a single form …
V = k/P, V = kT, and V = kn
V a (nT)/P
For initial and final conditions:
EOS
Chapter 5: Gases