Physical Chemistry

Question 1

What is the Empirical Approach ?

Answer 1

Information based on experimental results

Question 2

What is Boyles Law ?

Answer 2

Pressure and volume have an inverse relationship.

Question 3

What formula came from Boyles Law ?

Answer 3

pV = R

Question 4

What is Charles’ law ?

Answer 4

Volume of gas is directly proportional to the Absolute temperature.

Question 5

What formula was founded from Charles’ law ?

Answer 5

V = RT

Question 6

At a lower volume the pressure is …

Answer 6

highest

Question 7

What is Avogadro’s Law ?

Answer 7

Volume is directly proportional to the number of moles at the same Temperature and pressure.

Question 8

What equation came from Avogadro’s Law ?

Answer 8

V = Kn

Question 9

What is the Ideal Gas Law ? (Include the formula)

Answer 9

Links the Charles, Avogradro and Boyles laws together. (pV = nRT)

Question 10

What causes pressure ?

Answer 10

Particles colliding with the walls of the vessel

Question 11

What are the assumptions of Ideal Behaviour ?

Answer 11

1. Gases consist of particles that are in constant motion
2. The volume of particles is negligible
   Particles only interact with each other by randomly colliding
3. Collisions are elastic
4. Temp is related to the average Ek
   Pressure is caused by particles colliding with the walls of the vessel.

Question 12

What does elastic mean ?

Answer 12

Energy and momentum are conserved

Question 13

What is the formula relating Pressure, force and area ?

Answer 13

Pressure = Force/ area

Question 14

What is the formula relating Force, momentum and time ?

Answer 14

Force = Change in momentum/ Change in time

Question 15

Higher temp…. (HINT: Graph)

Answer 15

Wider distribution of molecular speed so average increases.

Question 16

What are the three ways a molecule can move ?

Answer 16

1. Translational motion
2. Rotational Motion
3. Vibrational Motion

Question 17

What is Molar Heat Capacity ?

Answer 17

Heat required to increase the temp of 1mol of a gas by 1K

Question 18

Why do diatomic require more heat to increase the temp compared to monatomic atoms ?

Answer 18

Their molecules can store more heat energy without increasing their translational kinetic energy as the molecules can rotate, vibrate and translate.

Question 19

How many vibrational modes do linear molecules have ?

Answer 19

3N - 5

Question 20

How many vibrational modes do non-linear molecules have ?

Answer 20

3N - 6

Question 21

What terms desribes when the energy of a substance is equally divided ?

Answer 21

Equi-partition

Question 22

How much does each translational and rotational degree of freedom contribute to internal energy ?

Answer 22

1/2RT

Question 23

How much does each vibrational mode contribute to internal energy ?

Answer 23

RT

Question 24

At low temp is translational, rotational or vibrational modes active ?

Answer 24

Translational

Question 25

At high temp, is translation, vibrational or rotational mode active ?

Answer 25

translation, vibrational and rotational

Question 26

What is Isotherm ?

Answer 26

Constant pressure

Question 27

When does the real gas law work (at what temp) ?

Answer 27

High temperature and Low temperature

Question 28

When does the Ideal gas law work ?

Answer 28

High temperature

Question 29

Why does the ideal gas law fail ?

Answer 29

- Intermolecular forces - Molecular size effect

Question 30

Why does Intermolecular forces fail the Ideal Gas law ?

Answer 30

At low temp, molecules have a low Ek and attractive forces start to influence gas behaviour. The attractive forces doninate and liquid will form. Whereas, at a high temperature, molecules have a high Ek and they overcome these weak vdW.

Question 31

Why does the Ideal gas law not work at high pressure ?

Answer 31

Molecules start to repel each other through the Pauli exclusion principle and electron repulsion- unlike at low temp where, the molecules won't interact very much.

Question 32

Why does Molecular size effect fail the ideal gas law ?

Answer 32

At a lower pressure, volume of molecule is neglible compared to volume of container. Where, at high pressure, volume of molecules is significant compared to container volume, molecules get in each others way.

Question 33

What is the formula used to account for Molecular size effect ?

Answer 33

P(V-nb) = nRT... where, n= number of moles, b= volume exluded by 1mol of molecules

Question 34

How does attractive forces have an effect on pressure ?

Answer 34

Will reduce the frequency of collisions and hence attractive forces cause pressure of real gas to be lower than Ideas gas law predicts.

Question 35

How does attractive forces differ with concentration ?

Answer 35

As conc increases, there is more molecules and hence more attractice forces.