u4: gases

Question 1

types of molecular motion

Answer 1

• vibrational (atoms within molecule/lattice)
• rotational (molecules move)
• translational (particles move)

Question 2

5 properties of gas

Answer 2

1. gases expand to fill any space available
2. occur larger than a liquid or solid of the same mass – Low Densities
3. most are colourless & odourless.
4. mixed together in any proportion to form a homogeneous solution provided they do not react.
5. volume, temperature & pressure of a gas are interrelated.

Question 3

kinetic molecular theory

Answer 3

1. any sample is made up of mostly empty space.
2. particles have a very high translational energy. They move in rapid straight line motion.
3. when gas particles collide with each other, or the walls of a container, the collision is elastic. no loss of kinetic energy when particles collide.
4. in gas phase, there are no attractive or repulsive forces.
5. at a given temperature, the average kinetic energy of the particles in all gases is the same.

Question 4

ideal gas

Answer 4

what satisfies the KMT

Question 5

real gases

Answer 5

• dont satisfy KMT
• experience forces of attraction at high pressures
• the volume of the particles become a significant proportion of the total volume at low temperatures.

Question 6

atmospheric pressure

Answer 6

• Results from mass of air being pulled toward the earth by gravity
• Varies with altitude and weather conditions

Question 7

pressure

Answer 7

measure of force/area

Question 8

celsius to kelvins

Answer 8

Tk = Tc + 273.15

Question 9

centimetre cubed

Answer 9

1 mL

Question 10

P1V1=P2V2

Answer 10

robert Boyle’s law
- P and V are inversely proportional: as pressure increases, volume decreases
- less spaces = particles hitting walls = more pressure

Question 11

V1/T1=V2/T2

Answer 11

jacques Charles law
- V and T are directly porportional: increase/decrease together

Question 12

P1/T1=P2/T2

Answer 12

Gay-Lussac’s Law
- P and T directly proportionate (temp. in kelvins): increase/decrease together

Question 13

Gay-Lussac’s “real” law

Answer 13

When temperature and pressure remain constant, the volumes of gaseous reactants and products are always in simple whole number ratios

Question 14

Avagadro’s Law

Answer 14

proposed that equal volumes of gases at the same temperature and pressure contain the same number of particles
- the volume of a gas is directly proportional to the amount of gas, when temperature and pressure remain constant
- V1/n1 = V1/n1

Question 15

ideal gas law

Answer 15

PV = nRT
- R is universal gas constant: 8.31
- pressure: kPa
- volume: Litres
- temp: kelvins

Question 16

Ptotal = Pa + Pb + Pc

Answer 16

• Dalton’s Law of Partial Pressure
• total pressure of a mixture of gases is equal to the sum of all the partial pressures of the gases making up the gas mixture

Question 17

P1V1/T1=P2V2/T2

Answer 17

combined gas law
- any units of pressure or volume can be used but temperature must be expressed in kelvins