Unit 4 - Gases

Question 1

Kinetic Molecular Theory (KMT)

Answer 1

1. A gas consists of an extremely large number of very tiny particles that are in constant, random motion. This is referred to as Brownian motion.
2. The gas particles occupy a relatively small volume, negligible to the volume of their container.
3. The gas molecules have very weak attractive forces for one another because of their very large distances apart.
4. Collisions of the gas particles with each other and with the walls of the container are perfectly elastic.
5. The average kinetic energy of the gas molecules is proportional to absolute temperature.

Question 2

STP
What are the values at STP for Temperature, Pressure, & Molar Volume of a gas

Answer 2

Standard Temperature and Pressure: 0 degrees Celsius, 101.3 kPa
V = 22.4 L.

Question 3

SATP

Answer 3

Standard Ambient Temperature and Pressure: 25 degrees Celsius, 100 kPa

Question 4

General gas laws

Answer 4

To describe the state or condition of a gas, it is important to specify four variables:
- Pressure (kPa)
- Temperature (K)
- Volume (L)
- Amount (moles)

Question 5

Charles Law

Answer 5

States:
The volume of a gas is directly proportional to the absolute temperature when the pressure and the amount are kept constant.
- The other 2 variables MUST be constant

K = V / T

OR

V1 V2
– = –
T1 T2

Question 6

Kelvin Scale

Answer 6

Both the Fahrenheit and Celsius scales are relative. They are based on the melting and boiling temperatures of water. The KELVIN SCALE is ABSOLUTE. The zero corresponds to the lowest temperature possible.

K = degrees Celsius + 273.

Question 7

Boyle’s Law

Answer 7

K = PV

GRAPH:
- As the volume increases, pressure decreases
Pressure is inversely proportional to the volume.

• Inverse pressure is directly proportional to the volume (1/P)
• PV is constant.
  (Would be a straight horizontal line on the graph is pressure is the X, and PRESSURE x VOLUME is on the Y.)

Question 8

Gay-Lussac’s Law

Answer 8

K = P/T

GRAPH:
- The pressure of a fixed amount of gas at a constant volume is directly proportional to the absolute temperature of the gas. So, as the temperature increases, the pressure also increases proportionally.

Question 9

The combined gas law

Answer 9

T1

• Combining Charle’s, Gay-Lussac’s, and Boyle’s

Question 10

Relation between average kinetic energy and temperature

Answer 10

• When the temperature is ABSOLUTE!!!
• The average kinetic energy of a molecule is directly proportional to its absolute temperature

Question 11

Dalton’s Law

Answer 11

Dalton’s Law of Partial Pressures:

• P(t) = P (a) + P (b) + P (c) …

Question 12

Avogadro’s Law

Answer 12

• At the same temperature and pressure, equal volumes of different gases contain an equal number of gas particles.

TALKS ABOUT relationship between volume and moles.

The molar volume of ANY gas at STP is 22.4 L/mol.

REMEMBER:
UNITS ARE L/mol.

Question 13

Ideal Gas Law:

Answer 13

COMPOSITION:
- An ideal gas consist of a large number of identical molecules

VOLUME:
- The volume of the gas particles themselves is negligible compared to the volume of the space surrounding them

ATTRACTIVE FORCES:
- The IMF between them is so weak that it is negligible

MOVEMENT:
- They move in random motion

TEMPERATURE:
- High

PRESSURE:
- Low

PV = nRT
- The ideal gas law allows us to use this equation.

Question 14

How to find the DENSITY:

Answer 14

D (density) = m (mass)/V (volume)

D = m / V

Question 15

REMEMBER:

Answer 15

• Absolute temperature
• STP

Question 16

True or False:
For any substance, the melting point and freezing point occur at the same temperature.

Answer 16

TRUE.