Gases

Question 1

What conditions best simulate ideal gas behavior?

Answer 1

High temperature and low pressure

Question 2

What are the terms used to describe the macroscopic measurements of a gas system? The microscopic measurements?

Answer 2

Macroscopic_______________________Microscopic
Pressure, P Collision freq & Collision force
Volume, V Mean free path
Moles, n Molecules
Temperature, T Average kinetic energy

Question 3

Collision Frequency

Answer 3

The collision frequency is defined as the rate at which molecules in the gas system collide with each other and with the wall of the container. The collision frequency can be increased in one of three ways: increasing the temperature (energy of the gas system), increasing the concentration of gas particles, or reducing the mean free path. All of these changes result in an increase in the number of collisions experienced by a molecule within the system in a given period of time.

Question 4

Collision Force

Answer 4

The collision force is defined as the force exerted by a gas particle during a collision between it and the container wall. It is an impulse, so both greater momentum and a shorter time of contact increase the force of impact. The collision force can be increased by increasing the temperature (energy of the gas system), because greater temperature imparts greater velocity, and thus greater momentum, to each particle.

Question 5

Mean Free Path

Answer 5

The mean free path is defined as the average distance a particle can travel before colliding with another particle. Although it isn’t the same thing, it can be thought of as the average distance between gas particles at anygiven time. It is the microscopic equivalent of concentration. If the concentration of a gas remains constant, then the average distance between any two particles within the container also remains constant.

Question 6

The kinetic molecular theory of gases

Answer 6

Particles are small, negligible volume
Particles move in straight lines, collisions elastic
Particles are in random translational motion
Particle exhibit no intermolecular forces

Question 7

Ideal gas follow three conditions

Answer 7

no intermolecular forces
point masses
all collisions are perfectly elastic

Question 8

Ideal gas law

Answer 8

PV=nRT

R=0.0821 (atmL)/(molK)

Better written as:

PV/(nT) = PV/(nT) = R

Question 9

Deviations from ideal gas law in pressure are due mainly to?

Answer 9

Intermolecular forces

think of the ‘a’ in correcting the value as ‘attraction coefficient’

Question 10

Deviations from ideal gas law in volume are due to?

Answer 10

The fact that the molecules have volume

think of the ‘b’ in correcting the value as the bigness coefficient

Question 11

For an inert real gas, if you were to reduce the pressure to half of its original value, then what is the final volume relative to the initial volume?
A. (1/2) V_i - a little bit
B. (1/2) V_i + a little bit
C. 2 V_i - a little bit
D. 2 V_i + a little bit

Answer 11

When pressure is cut in half, the ideal gas law predicts that volume should double. Because only the space between molecules increases, while the molecules remain the same size, the increase in volume is not as large as predicted by the ideal gas law. This makes choice C, 2V_i - a little bit, the best answer. The”little bit” term is attributed to the size of the molecules.

Question 12

Which momentum is greater: heavier gases or lighter gases?

Answer 12

Heavier gases have a greater momentum

Question 13

What is the partial pressure of gas a?

Answer 13

P_a = P_tot * (mole fraction of a)

Question 14

What is the root mean square velocity of a gas?

Answer 14

v_rms = sqrt(3RT/mm)

R=8.314 J/(mol*K)
mm= molar mass in kg/mol

Question 15

Graham’s law for gas flow

Answer 15

r1/r2 = sqrt(mm2/mm1)

it can also relate to temperature:
r1/r2 = sqrt(T2/T1)