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AP Chemistry > ch 10 gases > Flashcards

ch 10 gases Flashcards

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1
Q

characteristics of gases6

A
  • nonmetals
  • low molar masses
  • expand to fill container, V=volume of container
  • compressible: V decreases with pressure applied
  • form homogenous mixtures with other gases
  • not dense
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2
Q

vapor

A

substances that are liquids or solids under ordinary conditions that can also exist in the gaseous state. (H2O=liquid water, solid ice, water vapor)

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3
Q

pressure definition

A

a force, a push that tends to move something in a given direction.

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4
Q

pressure formula2

A

P=Force/Area
P=(density* Volumeacceleration)/Area
=densityheight*accel (acceleration=9.8)

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5
Q

Si units for force and pressure3

A

Force: 1 (kg-m)/s2=1N
Pressure: 1N/m2=1 Pa=1kg/(m-s2)
pressure also measured in bar: 1bar=10^5 Pa

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6
Q

barometer

A

(torricelli) is an instrument that measures pressure. The height that the mercury is in the column measures the pressure. Can have any cross section area

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7
Q

manometers3

A
  • like barometers but have two curves.
  • Open manometers: Pgas=Patm+Ph. Closed manometers: Pgas=h.
  • If h>0, P>1atm. If h<0, P<1atm
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8
Q

standard atmospheric pressure

A

typical pressure at sea level 1atm=760mmHg=760torr=1.01325*105Pa=101.325kPa

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9
Q

variables to define state of gas

A

4 variables are needed to define the state (physical condition) of gas: temperature T, pressure P, volume V, and amount (moles, n)

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10
Q

boyles law3

A

-Volume decreases as pressure increases.
-V=constant*1/P, PV=constant
-P1V1=P2V2
(V in liters)

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11
Q

charles law3

A

-Volume increases as temperature increases. -V=constant*T, V/T=constant
-V1/T1=V2/T2
(T in Kelvin)

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12
Q

gay-lussac law

A

-law of combining volumes: at a given temperature and pressure, the volumes of gases that react with one another are in ratios of small whole numbers (2 volumes of H2 react with 1 volume of O2 gas forming 2 volumes of H2O gas)

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13
Q

avogadros law4

A
  • as volume increases, moles increase
  • equal volumes of gases at the same temperature and pressure contain equal numbers of molecules (equal moles).
  • V=constant*n
  • V1/n1=V2/n2
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14
Q

ideal gas equation

A

PV=nRT, where R is the gas constant. The value and units of R depend on the units of P, V, n and T. T always =K. n always =moles.

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15
Q

values for gas constant3

A
  • 0.08206 L-atm/mol-K
  • 8.314J/mol-K or L-kPa/mol-K or m3-Pa/mol-K
  • 62.36L-torr/mol-K or L -mmHg/mol-K
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16
Q

STP2

A
  • standard temperature and pressure =0ºC and 1atm

- Molar volume of an ideal gas at STP= 22.41 L

17
Q

combined gas law

A

P1V1/T1=P2V2/T2

18
Q

density equation2

A

d=PM/RT, d=density, M=molar mass.

-Higher M and P =more dense, higher T=less dense.

19
Q

molar mass equation 2

A
  • M=dRT/P

- M=(grams gas*RT)/PV

20
Q

daltons law4

A
  • total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.
  • Partial pressure: pressure exerted by a particular component of a mixture of gases.
  • Pt=P1+P2+P3+…
  • Each gas behaves independently of the others.
21
Q

mole fraction and equations 2

A
  • dimensionless number that expresses the ratio of the number of moles of one component to the total number of moles in the mixture.
  • P1/Pt=n1/nt=X1
  • P1=(n1/nt)Pt=X1Pt
22
Q

collect gas over water

A

Ptotal=Pgas+PH2O

23
Q

kinetic molecular theory6

A
  • rudolf clausius, explains why gases behave the way they do.
  • molecules in constant random motion
  • molecules have negligible volume
  • intermolecular forces:negligible
  • Collisions between molecules do not change avg kinetic energy (elastic)
  • avg KE is proportional to temp
24
Q

molecular motion vs temp vs KE

A

molecular motion increases as temp increases as KE increases

25
Q

avg KE

A

is same for all molecules but every molecule has different speed. At higher temps, more molecules move at greater speeds.

26
Q

rms speed5

A
  • Root-mean-square (rms) speed, u: speed of a molecule possessing average kinetic energy.
  • The average kinetic energy of the gas molecules in a sample: e=1/2mass*u2,
  • Thus increase in avg kinetic energy as temp increases means increase in rms speed (avg speed)
  • lighter gas=high rms, heavy gas=low rms
  • u=sqrt(3RT/M) (R=8.314kgm2/s2molK, M=kg/mol)
27
Q

km theory explain PV relationship

A

constant temp means avg kinetic energy of gas remains unchanged, so rms is unchanged. So if volume is increased, molecules must move larger distance between collisions, so fewer collisions and pressure decreases

28
Q

km theory explain TP relationship

A

increase in temp means increase in avg kinetic energy and increase in u. IF no change in volume, more collisions with walls per unit of time, Momentum will increase and molecules strike wall more forcefully, so pressure increases.

29
Q

effusion

A

escape of gas molecules through a tiny hole into an evacuated space

30
Q

diffusion

A
  • spread of one substance throughout a space or throughout a second substance (molecules diffuse throughout a room)
  • much slower than molecular speeds because of molecular collisions, which occur because real gas molecules have finite volumes (reason you can’t smell perfume across the room instantly)
31
Q

graham law

A
  • r1/r2=sqrt(M2/M1), r1 and r2= rates of effusion under identical conditions.
  • smaller M=faster moving=greater likelihood that a molecule will hit the hole / effuse
32
Q

mean free path

A
  • The diffusion of a molecule consists of many short, straight line segments and at different speeds.
  • Mean free path: average distance traveled by a molecule between collisions.
  • high pressure=short mean free path
33
Q

deviation of real gas from ideal gas

A
  • PV/RT=n

- Negative deviation=result of forces, Positive deviation=result of volume

34
Q

Real gases not ideal 2

A
  • high P

- low T

35
Q

reasons for deviation

A
  • real molecules have finite volumes (at high P, combined volume of molecules is larger fraction of total space available)
  • do attract one another (at low T, molecules do not have enough KE to overcome intermolecular forces
36
Q

van der waals5

A
  • equation used to predict behavior of real gases
  • (P+n2a/V2)(V-nb)=nRT
  • a corrects for molecular attraction, b corrects for volume of molecules
  • smaller a/b=more ideal gas
  • a/b increase as mass of molecule increases

AP Chemistry (14 decks)

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