The gas laws Flashcards
Do gases have a fixed volume?
no
diffusion
the spreading out of a gas to fill a space
how do you demonstrate diffusion
cotton wool, one end soaked in HCl solution and the other in NH3 solution. ring of ammonium chloride forms between them
do the solutions move at the same rate in diffusion?
no, the lighter one generally moves faster
if temperature increases what happens to a gas
it expands
if pressure increases what happens to a gas
it is compressed, smaller volume
Boyle’s law
when a fixed mass of gas is kept at constant temperature, it’s volume multiplied by it’s pressure is constant
mathematical expression of Boyle’s law
p1V1 = p2V2
graph of boyles law, volume vs pressure, y axis
volume (cm cubed)
graph of boyles law, volume vs pressure, x axis
pressure (Pa)
how do you show that pressure is inversely proportional to volume
draw a graph of pressure vs 1/volume
straight line through the origin
Boyle’s law is true for all gases provided that..
the same units were used on both sides of the equation
graph of pV vs p
straight line horizontally
Charles’ law
the volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature
absolute temperature
temperature measured in kelvin
how do you get from ºc to K
add 273.15
how do you get from K to ºc
take away 273.15
where is the origin on the graph of volume vs temperature
0K (not 0ºc)
mathematical expression of Charles’ law
V1/T1 = V2/T2 where T is measured in kelvin
graph of V/T against T
straight horizontal line
Gay-Lusaac’s law of combining volumes
volumes of gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure
2 conditions for Gay-Lusaac’s law of combining volumes
everything has to be gaseous
same temperature and pressure
when can you not use moles when doing calculations
if everything is gaseous
same temperature and pressure
Avogadro’s law
equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules
for Gay-Lusaac’s law of combining volumes and avogadro’s law, does it have to be stp?
no just the same temperature and pressure, not just standard
first words of Gay-Lusaac’s law of combining volumes
volumes of gases
first words of Avogadro’s law
equal volumes of gases
The combined gas law // the general gas law
P1V1/T1 = P2V2/T2 temperature and pressure
what does the combined gas law // the general gas law come from
boyle’s and charles’ laws
where does avogadro’s law come from
Gay-Lusaac’s law of combining volumes
5 assumptions made by the kinetic theory of gases about gases
- their particles are widely separated, their volume is mostly empty space and do not occupy much space
- their particles are in constant random motion colliding with each other and walls of the container
- the collisions are elastic, no loss of energy as a result
- their particles are independent of each other. no attractive forces between them
- the average kinetic energy of the particles is proportional to the absolute temperature
3 reasons why ideal gases do not exist
+ 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
ideal gas
a gas that obeys all gas laws at all temperatures and pressures
when do real gases come closest to ideal behaviour
at low pressures and at high temperatures
under normal conditions
real gases behave similarly to ideal gases
3 reasons why real gases depart from ideal behaviour
+ 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
the equation of state for an ideal gas
PV = nRT
P
pressure in Pa or N/m squared
V
volume in m cubed
R
gas constant
T
temperature in kelvin
n
moles
how to get from KPa to Pa
multiply by 10 ³
how to get from cm cubed to m cubed
multiply by 10^-6
how to get from L to m cubed
multiply by 10-³
how to get from ºc to K
+ 273.15
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
8 pieces of apparatus
graduated gas syringe, hypodermic syringe, thermometer, container with steam inlet, self sealing rubber cap, electronic balance
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
material
a volatile liquid - propanone
propanone
CH3COCH3
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
first step
draw about 5cm³ of air into graduated gas syringe and place rubber cap on
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
after you put air into the graduated syringe
pass steam through the container until volume of air and temperature are steady and note these values
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
after you have noted values for temperature and volume
draw propanone into the hypodermic syringe and note the mass using an electronic balance
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
after propanone is in syringe and mass recorded
push the hypodermic syringe through the rubber cap and inject half of the propanone in
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
once propanone has been injected into the setup
note the plunger of the graduated cylinder moving out and note the new volume reading
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
once the new volume reading is noted
withdraw the hypodermic syringe and rerecord the mass
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
atmospheric pressure at the end
noted on the barometer
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
volume of vapour
final - initial
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
mass of vapour
initial - final
DETERMINING THE Mr OF A VOLATILE LIQUID USING A GAS SYRINGE
3 sources of error
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
