Physical Chemistry

Question 0

Define the term collision frequency, z?

Answer 0

The average number of collisions one molecule makes in a given time interval divided by the length of the interval.

Question 1

Define the mean free path, λ?

Answer 1

The average distance a molecule travels between collisions

Question 2

State Boyle’s Law.

Answer 2

At a constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume.

Question 3

State Charles’ law.

Answer 3

At a constant pressure, the volume of a fixed amount of gas varies linearly with the temperature

Question 4

State Avogadro’s principle.

Answer 4

At a given temperature and pressure equal volumes of gas contain the same number of molecules.

Question 5

What are the conditions defined by Standard Ambient Temperature and Pressure (SATP)?

Answer 5

• temperature at 298.15 K

- pressure at 1 bar (100 kPa)

Question 6

What is the molar volume of an ideal gas at SATP?

Answer 6

24.79 dm^3

Question 7

State Dalton’s law.

Answer 7

The pressure exerted by a mixture of ideal gasses is the same of the pressures that each gas would exert if it were alone in the container at the same temperature.

Question 8

What are the assumptions made by the kinetic theory model of gases?

Answer 8

1- a gas consists of molecules in constant random motion
2- the size of the gas molecules is negligible i.e. Their diameters are smaller than the average distance travelled between collisions
3- the molecules do not interact except during collisions
4- collisions between molecules are perfectly elastic
5- molecules are considered to be point masses

Question 9

Define the root mean-square speed, c?

Answer 9

The square root of the mean of the squares of the speed.

Question 10

What is diffusion?

Answer 10

Diffusion is the process by which molecules moving randomly move down a concentration gradient i.e. From an area of high concentration to an are of low concentration

• the molecules mingle
• the process is slow

Question 11

What is effusion?

Answer 11

Escape of gas through a small hole

Question 12

State Graham’s law of effusion.

Answer 12

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

Question 13

What is the relationship between the mean free path and an ideal gas?

Answer 13

An ideal gas is a gas for which the mean free path, λ or the molecules in the the sample is much greater than d, e separation at which the molecules are regarded as being in contact
-λ&raquo_space; d

Question 14

What are molecular interactions?

Answer 14

These are attractions and repulsion a that give rise to a potential energy. That contribute to the total energy of a gas.

Question 15

Define the term critical temperature.m

Answer 15

The temperature above which a gas cannot be condensed to a liquid by applying pressure.

Question 16

What is a supercritical fluid?

Answer 16

A substance above its critical temperature and pressure above which distinct liquid and gas phases do not exist

Question 17

What are some uses of supercritical fluids?

Answer 17

1- used as solvents i.e. Supercritical carbon dioxide used to extract caffeine in the manufacture of decaffeinated coffee
2- used in industrial processes i.e. Used instead of CFCs

Question 18

What is the compression factor, Z?

Answer 18

The ratio of the actual molar volume of a gas to the molar volume of a perfect gas under the same conditions.

Question 19

How does the compression factor, Z vary with pressure?

Answer 19

• at low pressures Z < 1

- at high pressures Z > 1