Gases

Question 1

KMT: 5 postulates

Answer 1

1. Gases are composed of small molecules that are in CONSTANT, RANDOM MOTION
2. The volume that is taken by the molecules themselves is insignificant compared with the overall volume occupied by the gas
3. Forces between the molecules are negligible, except when the molecules collide with each other
4. Molecular collisions are PERFECTLY ELASTIC (no energy is lost when the molecules collide)
5. The AVERAGE KINETIC ENERGY of the gas molecules is directly proportional to the absolute temperature of the gas

Question 1

Kinetic Molecular Theory

Answer 1

explains gas laws and some properties of liquids and solids - has 5 postulates

Question 2

Random Motion

Answer 2

POSTULATE 1

molecules travel in straight lines in any arbitrary direction until they hit other molecules or the walls of the container

Question 3

Perfectly Elastic Collision

Answer 3

POSTULATE 4

molecules bounce off one another without any loss of total energy - no friction or energy loss of any kind occurs

Question 4

Average Kinetic Energy

Answer 4

POSTULATE 5

the overall average of the kinetic energies of all individual molecules at any instant
- constant
- not all molecules have a constant, same KE at all times

Question 5

KMT: Pressure

Answer 5

POSTULATES 1+3

Gases are in constant motion and are colliding with each other. The force of the collisions is a source of pressure

Question 6

KMT: Volume

Answer 6

when volume decreases without a change in the number of particles, the rate of collision of those particles + container walls must increase, causing pressure to increase

BOYLES LAW

Question 7

KMT: Temperature

Answer 7

POSTULATE 5

an increase in temp causes gas particles to have increased energy and speeds. these faster-moving particles collide more often and with greater force, increasing pressure.

if container is flexible, the pressure remains constant and volume increases to accommodate the faster moving particles

CHARLES LAW

Question 8

KMT: # of Moles

Answer 8

when the number of moles increase, the rate of collisions of the particles and container walls increase

AVOGADROS LAW

Question 9

Root Mean Square Speed

Answer 9

• at LOWER temps, the average speed is low and range of speeds is narrow
• at HIGHER temps, the average speed is high and the range is spread out
• all gases have the same KE at a given temp, but a different speed that depends on the mass of the particles

Question 10

Diffusion

Answer 10

occurs when a gas sample is introduced into a larger volume, and the gas particles spread out to occupy the entire volume
- rate of diffusion depends on temperature, mass of the particle, and collisions

Question 11

Mean Free Path

Answer 11

average distance traveled between collisions
- is related to the pressure of the gas particles
- increase in pressure, increase in particles per unit volume, increase in collisions, decrease in mean free path

Question 12

Effusion

Answer 12

the escape of gas molecules through a tiny hole into a vacuum/region of lower pressure
- does NOT depend on collisions

Question 13

Graham’s Law of Effusion

Answer 13

ratio of effusion of two gases

Question 14

Ideal Gas Behaviors

Answer 14

TWO KEY ASSUMPTIONS
1. volume of gas particles is negligible
2. there are NO interactions, attractive or repulsive, between gas particles

Question 15

Real Gas Behaviors

Answer 15

• have finite volumes
• when very high pressures compress the gas sample into small volumes, that finite volume of the particles is NOT negligible
• as pressure increases and volume decreases, the volume taken up by particles becomes a higher % of the volume of the sample
• real gas particles form attraction through intermolecular forces (higher temperature = less attractions)
• Van der Waals Equation

Question 16

Van der Waals Equation

Answer 16

used for calculations of gas pressures (REAL GASES)