Gas Phase

Question 1

What is an ideal gas?

Answer 1

A gas with NO intermolecular forces and occupies no volume.

It is NEGLIGIBLE!

Question 2

Which units are gases measured in?

Answer 2

1 atm = 760 mmHg = 760 torr = 101.3 kPa

Question 3

What is the equation for ideal gas law?

Answer 3

Question 4

At STP, how many liters does a mole of gas occupy?

Answer 4

At STP, a mole of gas occupies 22.4 L.

Question 5

When the temperature and pressure of a gas is constant, what is the equation for Avogadro’s principle?

Answer 5

Question 6

For gases, what does Avogadro’s Principle state?

Answer 6

At constant temperature and pressure:

Moles of gas (n) and volume (V) are directly proportional.

(n ∝ V)

Question 7

For gases, what does Boyle’s Law state?

Answer 7

At constant temperature:

Volume (V) of a gas is inversely proportional to its pressure (P).

(P = 1/V)

Question 8

What does Charles’ Law state?

Answer 8

At constant pressure:

Volume (V) of a gas is directly proportional to its temperature (T).

(V ∝ T)

Question 9

What does Gay-Lussac’s Law state?

Answer 9

At constant volume:

Pressure (P) of a gas is directly proportional to its temperature (T).

(P ∝ T)

Question 10

What does Dalton’s Law of partial pressures state?

Answer 10

The total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas.

Equation: P_T = P_A + P_B + P_C + …

Question 11

For Graham’s Law of Diffusion and Effusion, what is the difference between diffusion and effusion?

Answer 11

Diffusion: When gases mix with one another.

(an area of high concentration to low concentration)

Effusion: When gases escape through a small hole under pressure.

Question 12

What are the five assumptions for gases made by the kinetic molecular theory?

Answer 12

1. negligible volume of gas particles
2. random motion
3. NO intermolecular forces
4. elastic collisions
5. absolute temperature ∝ energy

Question 13

If gases have the same temperature and the same kinetic energy, how do they move?

Answer 13

• Large gases move slow.
• At high temperatures gases move fast.

Question 14

[Mnemonic]

a is the van der Waals term for the attractive forces.

b is the van der Waals term for big particles.

(how to remember what the a and b variable designate for the van der Waals state equation)

Answer 14

a is the van der Waals term for the attractive forces.

b is the van der Waals term for big particles.

Question 15

Under which conditions will a gas follow “ideal” behavior?

Answer 15

• High temperatures
• Low pressures

(Think 273 K and 1 atm.)

Ideal gases have weak intermolecular forces and NO volume.

Question 16

Under which conditions will a gas follow “real” behavior?

Answer 16

• Low temperatures (phase changes)
• High pressures (volume becomes significant and can’t be ignored)

Under these conditions gases deviate from ideal behavior.

Question 17

Which gases behave more like ideal gases? Why?

Answer 17

Noble gases (especially He) and Nonpolar molecules

Because they have the weakest intermolecular forces.

Question 18

When gases do NOT behave ideally, which equation should be used?

Answer 18

van der Waals state equation