Flashcards in ch 8 - The Gas Phase Deck (34)

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1

## four variables that define the state of a gaseous sample

### pressure (P), volume (V), temperature (T), and number of moles (n)

2

## gas pressure units

### atmospheres (atm) or millimeters of mercury (mmHg), which are equivalent to torr; SI unit is the pascal (Pa); mathematical relationship between all of these: 1 atm = 760 mmHg = 760 torr = 101.325 kPa

3

## standard temp and pressure (STP)

### conditions at 273 K (0 degrees C) and 1 atm; generally used for gas law calculations

4

## standard state conditions

### 298 K, 1 atm, 1 M concentrations; used when measuring standard enthalpy, entropy, free energy changes and electrochemical cell voltage

5

## ideal gas

### represents a hypothetical gas with molecules that have no intermolecular forces and occupy no volume

6

## ideal gas law

### PV = nRT; where P = pressure, V = volume, n = number of moles, T = temp, R = ideal gas constant (8.21 x 10^-2 L x atm/mol x K or 8.314 J/K x mol which is derived when SI units of Pa and cubic meters (for volume) are substituted into the ideal gas law

7

## density (fancy p)

### ratio of the mass per unit volume of a substance; usually expressed for gases in units of grams per liter; density derived from ideal gas law: PV = nRT; n = m/Molar mass; PV = (m/molar mass) RT and density = m/V = P(molar mass)/RT

8

## how much space does a mole of an ideal gas at STP occupy?

### 22.4 L

9

## combined gas Law

### can be used to relate changes in temp, volume, and pressure of gas: Psub1Vsub1/Tsub1 = Psub2Vsub2/Tsub2; where the subscripts 1 and 2 refer to the two states of the gas; this equation assumes number of moles stays constant

10

## change in volume

### Vsub2 = Vsub1[Psub1/Psub2][Tsub1/Tsub2]

11

## change in volume used to find density

### density = m/Vsub2

12

## molar mass from density

### molar mass = (density at STP)(22.4 L/mol)

13

## Avogadro's principle

### states that all gases at a constant temp and pressure occupy volumes that are directly proportional to the number of moles of gas present; equal amounts of all gases at the same temp and pressure will occupy equal volumes: n/V = k or nsub1/Vsub1 = nsub2/Vsub2; k = a constant; nsub1 and nsub2 = number of moles of gas 1 and gas 2; Vsub1 and Vsub2 = volumes of gases 1 and 2

14

## Boyle's Law

### for a given gaseous sample held at constant temp (isothermal), the volume of the gas is inversely proportional to its pressure: PV = k or Psub1Vsub1 = Psub2Vsub2; k = a constant; subscripts 1 and 2 = different sets of pressure and volume condidtions; in terms of gas law, n and T are constant here... As pressure increases volume decreases

15

## Charles's Law

### states that, at constant pressure, volume of a gas is proportional to its absolute temp in kelvins: V/T = k or Vsub1/Tsub1 = Vsub2/Tsub2; k = proportionality constant; subscripts 1 and 2 = two different sets of temp and volume conditions; n and P (with reference to ideal gas law) are held constant... as temp increases, volume increase

16

## Gay-Lussac's law

### relates pressure to temp: P/T = k or Psub1/Tsub1 = Psub2/Tsub2; subscripts 1 and 2 = two different sets of temp and pressure conditions; n and V (in terms of ideal law) are constant; as temp increases, pressure increases

17

## combined gas law

### combination of many of the preceding laws; relates pressure and volume in numerator, and variations in temp to both volume and pressure

18

## Dalton's Law of partial pressures

### if two or more gases that do not chemically interact are found in the same container each one will act independently of the other; law states total pressure of a gaseous mixture is equal to the sum of the partial pressure of the individual components

19

## partial pressure

### pressure exerted by each gas in a container where multiple gases that do not chemically interact are found

20

## Dalton's Law equation

### PsubT = PsubA + PsubB + PsubC + etc..; where PsubT = total pressure in container; PsubA through C = partial pressures of respective gases

21

## determining partial pressure

### PsubA = (XsubA)(PsubT); where XsubA = moles of gas A/total moles of gas and PsubT = total pressure of container

22

## vapor pressure

### pressure exerted by evaporated particles above the surface of a liquid

23

## Henry's Law

### [A] = ksubH x PsubA or [A]sub1/Psub1 = [A]sub2/Psub2 = KsubH; [A] = concentration of A in solution; ksubH = Henry's constant; PsubA = partial pressure of A

24

## kinetic molecular theory

### used to explain the behavior of gases; assumptions are: 1. Gases are made up of particles with volumes that are negligible compared to volume of container; 2. gas atoms or molecules exhibit no intermolecular attractions or repulsions; 3. Gas particles are in continuous, random motion, undergoing collisions with other particles and the container walls; 4. Collisions bt any two gas particles or particles and container are elastic meaning conserving momentum and kinetic energy; 5. avg kinetic energy of gas particles is proportional to the absolute temp of the gas (in kelvins), and it is the same for all gases at a given temp

25

## kinetic energy of a gas particle

### KE is proportional to the absolute temp of gas: KE = 1/2mv^2 = 3/2ksubB(T); where ksubB = Boltzmann constant (1.38 x 10^-23 J/K)

26

## Boltzmann constant

### 1.38 x 10^-23 J/K, serves as a bridge between macroscopic and microscopic behaviors of gases (as a bridge between behavior of the gas as a whole and the individual gas molecules)

27

## root-mean-square speed (u sub rms)

### a way to define the average speed of gases, determined by the average kinetic energy per particle and then calculating the speed which corresponds to it; given by the equation: u sub rms = square root of (3RT/M); R = ideal gas constant; T = temp, M = molar mass

28

## Maxwell-Boltzmann distribution curve

### shows the distribution of gas particle speeds at a given temp

29

## Graham's Law

### under isothermal and isobaric conditions, rates at which two gases diffuse are inversely proportional to the square roots of their molar masses: r sub 1/r sub 2 = square root of (Msub2/Msub1); r1 and r2 are diffusion rates of gases 1 and 2; M1 and M2 are molar masses of gases 1 and 2; noted that a gas with 4 times the molar mass of another gas will travel half as fast as the lighter gas

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