Chapter 7 - Ideal Gases

Question 1

Define one mole? (3)

Answer 1

One mole of any substance is the amount of that substance which contains the same number of particles as there are in 0.012kg of carbon-12.

Also:

• relative atomic mass of that substance in grams.
• a mole contains a standard number of particles - Avogadro constant = 6.02x10^23 per mole

Question 2

Define Boyle’s Law?

Answer 2

The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas remains constant.

Question 3

Boyle’s law equation?

Answer 3

pV=constant

p=k x 1/V

p1V1 = p2V2

Question 4

What are the 4 measurable properties of gases and two definitions?

Answer 4

Pressure (Pa) = force exerted normally per unit area by the gas on the walls of the container.
Temperature
Volume - measure of space occupied by the gas
Mass (kg or g)

Question 5

Pressure is proportional to?

Answer 5

1/V

Question 6

p1V1 = ?

Answer 6

p2V2

Question 7

pV = ?

Answer 7

Constant

Question 8

pV/T = ?

Answer 8

Constant

Question 9

p1V1/T1 = ?

Answer 9

p2V2/T2

Question 10

Ideal gas = ?

Answer 10

A gas that behaves according to the equation pV = NkT and pV = nRT.

Question 11

When do gases often stop being ideal?

Answer 11

At extreme temperatures

Question 12

For a gas consisting of N particles?

Answer 12

pV = NkT

k is Boltzmann constant = 1.38x10^-23 JK^-1

Question 13

For a gas consisting of n moles?

Answer 13

pV = nRT

R is universal molar gas constant

8.31Jmol^-1K^-1

Question 14

Na (Avogadro constant) = ?

Answer 14

R/k

Question 15

Number of moles = ?

Answer 15

Mass(g) / molar mass (g/mol)

Question 16

MTKE?

Answer 16

The mean translation kinetic energy of an atom (or molecule) of an ideal gas is proportional to the thermodynamic temperature.

Question 17

Mean translational kinetic energy is proportional to = ?

Answer 17

T

Question 18

MTKE = ?

Answer 18

(Sum of KE of atoms)/(no. of atoms)

OR

Average KE of one molecule over time

Question 19

Where do monatomic and diatomic molecules get their KE from?

Answer 19

Monatomic - only translational KE

Diatomic - both translational and rotational KE

Question 20

MTKE of ideal gas = ?

Answer 20

E = 1.5kT

Question 21

Describe Maxwell-Boltzmann distribution? (3 points too)

Answer 21

Y axis - number of molecules
X axis - speed of molecules

• not symmetrical
• mean speed increases with temperature
• mean speed > most probable speed

Question 22

KE is proportional to ?

Answer 22

T

V^2

Question 23

5 assumptions for kinetic model of ideal gases?

Answer 23

• gas contains v. large no. of spherical particles.
• forces between particles are negligible, except during collisions.
• volume of the particles is negligible compared to the volume occupied by gas.
• most of time, particle moves in straight line at constant velocity. The time of collision with each other/walls of container is negligible compared with time between collisions.
• collisions between particles are perfectly elastic so no KE is lost.