Unit 8: Gases

Question 1

describe the volume and shape of gases

Answer 1

indefinite volume and shape

Question 2

do gases tend to have low or high densities

Answer 2

low densities

Question 3

are gases easily able to mix with other gases

Answer 3

yes, mix with one another readily

Question 4

what condition causes a dramatic change in the volume of a gas

Answer 4

changing temperature

Question 5

what are common units of pressure

Answer 5

• mmHg
• torr
• atm
• Pa
• kPa
• psi

Question 6

what are the conversions for units of pressure

Answer 6

• 1 mmHg = 1 torr
• 1 atm = 760 mmHg / torr
• 1 atm = 101.3 kPa
• 1 atm = 14.7 psi

Question 7

how is the pressure exerted by a gas measured

Answer 7

• the frequency of collisions between gas molecules and the container walls
• more collisions = higher pressure

Question 8

what happens to pressure when volume decreases

Answer 8

pressure increases

Question 9

describe boyle’s law

Answer 9

pressure and volume are inversely proportional

Question 10

what is the equation for the relation between pressure and volume

Answer 10

P1V1 = P2V2

Question 11

what happens to volume when temperature decreases

Answer 11

volume decreases

Question 12

describe charles’s law

Answer 12

volume and temperature are directly proportional

Question 13

what is the equation for the relation between volume and temperature

Answer 13

V1/T1 = V2/T2

Question 14

what unit of temperature must be used in all gas law calculations

Answer 14

kelvin

Question 15

how do you convert celsius to kelvin

Answer 15

273.15 + C

Question 16

what happens to volume when moles increase

Answer 16

volume increases

Question 17

describe avogadro’s law

Answer 17

moles and volume are directly proportional

Question 18

what is the equation for the relation between moles and volume

Answer 18

V1/n1 = V2/n2

Question 19

what formula can be used to combine all the individual gas laws

Answer 19

P1V1/n1T1 = P2V2/n2T2

Question 20

what happens to pressure when moles decrease

Answer 20

pressure decreases

Question 21

are moles and pressure directly or inversely proportional

Answer 21

directly proportional

Question 22

define the ideal gas law

Answer 22

implies that all gases behave the same way under the same conditions

Question 23

what is the equation for the ideal gas law

Answer 23

PV=nRT

Question 24

what does R equal

Answer 24

• PV/nT
• 0.0821 Latm/molK

Question 25

what is the equation for density of gases

Answer 25

d=P(MW)/RT

Question 26

are density and temperature inversely or directly proportional

Answer 26

inversely proportional

Question 27

which gases are more dense: higher or lower molecular weights

Answer 27

higher molecular weights = more dense gas

Question 28

describe dalton's law of partial pressures

Answer 28

- Ptotal = P1 + P2 + P3 ... - the pressures of the different types of gases in a sample will add to be the total pressure of the entire sample - each gases pressure can be determined by multiplying the total pressure by the mole fraction of a gas (mols of one type of gas / total mols)

Question 29

what are the steps to determining the mass of a gas through stoichiometry

Answer 29

1. use ideal gas law (PV=nRT) to determine moles of gas 2. perform stoichiometric conversion to get to grams

Question 30

what are the steps to determining the volume, pressure, or temperature of a gas through stoichiometry

Answer 30

1. perform stoichiometry conversions to determine the moles of a gas 2. use ideal gas law (PV=nRT) to determine the volume, pressure, or temperature

Question 31

what are the 5 pillars of kinetic molecular theory

Answer 31

- gases consist of large number of molecules that move continuously and randomly - the combined volume of the gas molecules is negligible compared to the total volume in which the gas is contained - attractive and repulsive forces between gas molecules are negligible because they are moving so fast past each other - the average kinetic energy of the molecules is proportional to the absolute temperature (K) - all collisions are elastic; no energy lost

Question 32

is the kinetic energy of gas molecules directly or inversely proportional to temperature (in K)

Answer 32

- directly proportional - as temperature increases, the kinetic energy increases

Question 33

are molecular weight and average molecular speed directly or inversely proportional

Answer 33

- inversely proportional - as molecular weight decreases, speed increases (smaller molecules are faster)

Question 34

are gases more ideal at low or high pressures and why

Answer 34

- low pressures (0-20 atm) - low pressure = higher volume = size of molecules is more negligible

Question 35

are gases more ideal at low or high temperatures and why

Answer 35

- high temperatures - high temp = high speed = less time molecules spend near each other = less attractive/repulsive forces