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Chemistry (Tara) > The gas laws > Flashcards

The gas laws Flashcards

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1
Q

Do gases have a fixed volume?

A

no

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2
Q

diffusion

A

the spreading out of a gas to fill a space

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3
Q

how do you demonstrate diffusion

A

cotton wool, one end soaked in HCl solution and the other in NH3 solution. ring of ammonium chloride forms between them

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4
Q

do the solutions move at the same rate in diffusion?

A

no, the lighter one generally moves faster

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5
Q

if temperature increases what happens to a gas

A

it expands

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6
Q

if pressure increases what happens to a gas

A

it is compressed, smaller volume

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7
Q

Boyle’s law

A

when a fixed mass of gas is kept at constant temperature, it’s volume multiplied by it’s pressure is constant

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8
Q

mathematical expression of Boyle’s law

A

p1V1 = p2V2

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9
Q

graph of boyles law, volume vs pressure, y axis

A

volume (cm cubed)

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10
Q

graph of boyles law, volume vs pressure, x axis

A

pressure (Pa)

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11
Q

how do you show that pressure is inversely proportional to volume

A

draw a graph of pressure vs 1/volume

straight line through the origin

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12
Q

Boyle’s law is true for all gases provided that..

A

the same units were used on both sides of the equation

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13
Q

graph of pV vs p

A

straight line horizontally

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14
Q

Charles’ law

A

the volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature

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15
Q

absolute temperature

A

temperature measured in kelvin

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16
Q

how do you get from ºc to K

A

add 273.15

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17
Q

how do you get from K to ºc

A

take away 273.15

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18
Q

where is the origin on the graph of volume vs temperature

A

0K (not 0ºc)

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19
Q

mathematical expression of Charles’ law

A

V1/T1 = V2/T2 where T is measured in kelvin

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20
Q

graph of V/T against T

A

straight horizontal line

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21
Q

Gay-Lusaac’s law of combining volumes

A

volumes of gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure

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22
Q

2 conditions for Gay-Lusaac’s law of combining volumes

A

everything has to be gaseous

same temperature and pressure

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23
Q

when can you not use moles when doing calculations

A

if everything is gaseous

same temperature and pressure

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24
Q

Avogadro’s law

A

equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules

25
Q

for Gay-Lusaac’s law of combining volumes and avogadro’s law, does it have to be stp?

A

no just the same temperature and pressure, not just standard

26
Q

first words of Gay-Lusaac’s law of combining volumes

A

volumes of gases

27
Q

first words of Avogadro’s law

A

equal volumes of gases

28
Q

The combined gas law // the general gas law

A

P1V1/T1 = P2V2/T2 temperature and pressure

29
Q

what does the combined gas law // the general gas law come from

A

boyle’s and charles’ laws

30
Q

where does avogadro’s law come from

A

Gay-Lusaac’s law of combining volumes

31
Q

5 assumptions made by the kinetic theory of gases about gases

A
  1. their particles are widely separated, their volume is mostly empty space and do not occupy much space
  2. their particles are in constant random motion colliding with each other and walls of the container
  3. the collisions are elastic, no loss of energy as a result
  4. their particles are independent of each other. no attractive forces between them
  5. the average kinetic energy of the particles is proportional to the absolute temperature
32
Q

3 reasons why ideal gases do not exist

A

+ there are attractive forces (VdW)
+ the amount of space occupied is significant especially under high pressure
+ collisions are not all perfectly elastic as energy can be lost to surroundings

33
Q

ideal gas

A

a gas that obeys all gas laws at all temperatures and pressures

34
Q

when do real gases come closest to ideal behaviour

A

at low pressures and at high temperatures

35
Q

under normal conditions

A

real gases behave similarly to ideal gases

36
Q

3 reasons why real gases depart from ideal behaviour

A

+ there are forces of attraction between molecules
+ the amount of space occupied is significant especially under high pressure
+ collisions are not all perfectly elastic as energy can be lost to surroundings

37
Q

the equation of state for an ideal gas

A

PV = nRT

38
Q

P

A

pressure in Pa or N/m squared

39
Q

V

A

volume in m cubed

40
Q

R

A

gas constant

41
Q

T

A

temperature in kelvin

42
Q

n

A

moles

43
Q

how to get from KPa to Pa

A

multiply by 10 ³

44
Q

how to get from cm cubed to m cubed

A

multiply by 10^-6

45
Q

how to get from L to m cubed

A

multiply by 10-³

46
Q

how to get from ºc to K

A

+ 273.15

47
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

8 pieces of apparatus

A

graduated gas syringe, hypodermic syringe, thermometer, container with steam inlet, self sealing rubber cap, electronic balance

48
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

material

A

a volatile liquid - propanone

49
Q

propanone

A

CH3COCH3

50
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

first step

A

draw about 5cm³ of air into graduated gas syringe and place rubber cap on

51
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

after you put air into the graduated syringe

A

pass steam through the container until volume of air and temperature are steady and note these values

52
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

after you have noted values for temperature and volume

A

draw propanone into the hypodermic syringe and note the mass using an electronic balance

53
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

after propanone is in syringe and mass recorded

A

push the hypodermic syringe through the rubber cap and inject half of the propanone in

54
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

once propanone has been injected into the setup

A

note the plunger of the graduated cylinder moving out and note the new volume reading

55
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

once the new volume reading is noted

A

withdraw the hypodermic syringe and rerecord the mass

56
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

atmospheric pressure at the end

A

noted on the barometer

57
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

volume of vapour

A

final - initial

58
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

mass of vapour

A

initial - final

59
Q

DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE

3 sources of error

A

accuracy of measuring instruments eg. mass balance
air bubbles in hypodermic syringe
there is no such thing as an ideal gas and we use the ideal gas equation to calculate this

Chemistry (Tara) (50 decks)

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