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Question 1

What is broken during a phase change?

Answer 1

Only intermolecular attractions BETWEEN molecules are broken, not covalent bonds within the molecules.

Question 2

Sketch a p-V isotherm for three different temperatures.

Answer 2

See notes.

Question 3

On an isobar curve, at what temperature do all the lines intersect?

Answer 3

T = -273.15°C

Or T = 0K

Question 4

State Avogadro’s Law.

Answer 4

Equal volumes of gases contain equal numbers of molecules.

Question 5

State the assumptions of an ideal gas.

Answer 5

• the particles have no volume
• the particles do not attract or repel the other particles
• no rotational or vibrational kinetic energy
• no intermolecular forces
• no electrostatic potential energy

Question 6

At what temperature and pressure do gases behave almost ideally?

Answer 6

p: 1 bar and T: 300K

Gases behave almost ideally occupying 1/1000th

Question 7

State what is meant by SATP and the conditions.

Answer 7

SATP: Standard Ambient Temperature and Pressure.

298.15K (25°C) and 1 bar (1x10^5 Pa)

Question 8

Under SATP, what volume does one mole of an ideal gas have?

Answer 8

0.0248m^3

Question 9

State Dalton’s Law.

Answer 9

The pressure exerted by a mixture of gases is the sum of the partial pressures of the gases.

Question 10

What are the consequences of the assumptions of an ideal gas?

Answer 10

• internal energy of an ideal gas may be directly determined from the temperature
• the thermodynamic state may be specified by any two of the pressure, volume + temperature

Question 11

Explain why an ideal gas is an imaginary/hypothetical construct.

Answer 11

• an ideal gas consists of perfectly spherical particles of zero volume that may only collide elastically
• may only possess internal energy in the form of the translational kinetic energy of the particles

Question 12

State the typical value of momentum.

Answer 12

x10^-26 unless multiplied by Avogadro’s number

Question 13

Explain the relationship between kinetic energy and mass.

Answer 13

• a molecule with higher mass has greater kinetic energy

- if molecules have the same mass, the one moving faster has greater kinetic energy

Question 14

Sketch the graph for the distribution of molecular speeds and annotate.

Answer 14

See notes

Question 15

Sketch the graph for the effect of temperature on speed and explain.

Answer 15

See notes for graph.
As temperature increases:
- the most probably value increases
- the number of molecules at this speed decreases
- the average speed of a molecule increases

Question 16

Explain the effect of mass on speed.

Answer 16

As the mass increases:

• the molecules move slower
• the average speed is lower
• the distribution of speeds is less broad

Question 17

State Graham’s Law of Effusion.

Answer 17

At a given temperature and gas pressure, the rate of effusion is inversely proportional to the square root of the molar mass.

Question 18

State what is meant by effusion.

Answer 18

The number of molecules passing through the hole per second (see pg. 49 booklet 1)

Question 19

State the difference in the gas models for collisions.

Answer 19

• ball and stick model of gases allows us to see where all the atoms are
• hard sphere modern allows us to see how close molecules can get to each other

Question 20

What is the collision frequency (Z)?

Answer 20

The mean number of collisions per second. Can be found if we have the mean speed and the collision cross-section.

Question 21

What is the mean free path?

Answer 21

The average distance a molecule travels between collisions at a given temperature and pressure.

Question 22

In which cases do we use the root mean square of the molecular speeds?

Answer 22

• mean kinetic energy

- pV

Question 23

In which cases do we use the mean speed?

Answer 23

• effusion
• collision frequency
• mean free path

Question 24

Sketch the graph comparing the behaviour of an ideal gas and a real gases. Annotate.

Answer 24

For pressure vs 1/volume: the observed matches the ideal for LOWER pressures, not high pressures.
For temperature changes: observed matches ideal for HIGHER temperatures, not lower temperatures.

Question 25

What is the significant of 31.04°C?

Answer 25

It is the critical temperature for CO2; the maximum temperature at which liquid CO2 can exist.

• above this, CO2 is a gas at all pressures
• below this, CO2 shows a liquid phase at high pressures

Question 26

State all the attractive interactions in real gases and their energies.

Answer 26

• hydrogen bond 10-40 kJmol-1
• London dispersion ~5 kJmol-1
• dipole-dipole interaction 2 kJmol-1
• dipole-induced-dipole <2 kJmol-1

Question 27

Which bonds don’t we class as attractive interactions and why?

Answer 27

Ionic, covalent and metallic bonds. They are so strong they bond atoms together permanently.