Chapter 20: Gases

Question 1

What is the pressure of a gas?

Answer 1

The force per unit area that the gas exerts normally on a surface. Pressure is measured in pascals 1PA = 1Nm-1

Question 2

What does Boyle’s Law state?

Answer 2

For a fixed mass of gas at a constant temperature,

pV = constant

where p is gas pressure and v is volume

Question 3

What does Charles Law state?

Answer 3

For a fixed mass gas at constant pressure varies with absolute temperature,

V/T = constant
The graph is a straight line going through the origin.

Question 4

What does the pressure Law state?

Answer 4

The pressure of a fixed mass of gas at constant volume can be measured at different temperatures.

P/T = constant

If the measurements are plotted, on a graph of pressure against temperature in kelvin s they give a straight line graph through the origin.

Question 5

What is Brownian motion?

Answer 5

The unpredictable motion of particles suspended in a medium as a result of continuous bombardment by their surroundings.

Question 6

What is avogadro constant?

Answer 6

Avogradros constant NA The number of atoms in exactly 12g of the carbon isotope 12C6. The value of NA is 6.023 x 10^23

Question 7

What is one atomic mass unit?

Answer 7

1/12th of the mass of a 12C^ atom. The mass of a carbon atom is 1.993x10-26 so 1u = 1.661 x 10^-27

Question 8

What is one mole

Answer 8

The quantity of substance that contains NA particles, the number of moles in a give quantity of the substance is its molarity. The unit of molarity is the mol

Question 9

What is molar mass?

Answer 9

The mass of 1 mol of the substance, the unit of molar mass is kg mol-1. For example, the molar mass of oxygen gas is 0.032kgmol^-1

Number of moles in a substance Ms/M where M is the molar mass

The number of molecules in mass Ms of a substance NAMs/M

Question 10

What is the ideal gas and its equation?

Answer 10

An ideal gas is a gas that obeys Boyle’s law. The three laws can be combined to give pV/T = constant for a fixed mass of ideal gas

pV = nRT

Question 11

What is a molar gas constant?

Answer 11

Molar gas constant R = For q mol of any ideal gas, the value of PV/T is equal to 8.31 Jmol-1K-1

Question 12

What is the equation to calculate number of moles?

Answer 12

Ms - mass
M - molar mass
n = number of moles

Ms = M x n

n also = PV/RT

Question 13

How to calculate mass of a ideal gas?

Answer 13

Ms = M x pV/RT

Question 14

How to calculate density of an ideal gas of molar M

Answer 14

p = Ms/V

or NM/V

or pM/RT

Question 15

What is Boltzmann constant?

Answer 15

Boltzmann constant k = R/NA, and N is the number of molecules. It relates the average kinetic energy of a particle in a gas with the temperature of the gas.

Question 16

Explain pressure law

Answer 16

The pressure law can be explained as follows. The pressure of a gas
at constant volume is increased by raising its temperature. The average
speed of the molecules is increased by raising the gas temperature.
Therefore, the impacts of the molecules on the container walls are
harder and more frequent. So the pressure is raised as a result.

Question 17

What assumptions are made in kinetic theory equation?

Answer 17

• The molecules are point molecules. The volume of each molecule
  is negligible compared with the volume of the gas.
• They do not attract each other. If they did, the effect would be to
  reduce the force of their impacts on the container surface.
• They move about in continual random motion.
• The collisions they undergo with each other and with the
  container surface are elastic collisions (i.e., there is no overall loss
  of kinetic energy in a collision).
• Each collision with the container surface is of much shorter