Gas Laws and the Mole Flashcards
mole
The amount of a substance which contains 6.023 x 10²³ particles of that substance
(Avogadro’s number or constant = L)
kelvin
Celsius + 273
standard temp
273 K
normal temp
293 K
standard pressure
1 x 10⁵ Pa / 100,000 Pa
100 kPa
litre and cm³
1 litre = 1000 cm³
Boyle’s Law
States that: at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure
Charles’ Law
States that: at constant pressure, the volume of a fixed mass of a gas is directly proportional to its temperature measured on the Kelvin scale
V ∝ T
General Gas Law
hback
Gay Lussac’s Law of combining volumes
the volume of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temp + pressure
Avogadro’s Law
state that: equal volumes of gases contain equal numbers of molecules under the same conditions of temp + pressure
Molar Volume
at standard temp + pressure (s.t.p) one mole of any gas occupies 22.4 litres/dm³
at r.t.p: 24 litres/dm³
s.t.p
standard temperature + pressure
r.t.p
room temperature + pressure
Ideal Gas
one which perfectly obeys all the gas laws + all the assumptions of the kinetic theory of gases under all conditions of temperature + pressure
Gas
a substance that has no well defined boundaries but diffuses rapidly to fill any container in which it was placed
Pressure
The pressure of a gas is the force that the gas exerts on each unit area (eg. one square meter) of its container
Si unit of pressure
Newton per meter squared (N’m²)
Also called the pascal (Pa)
Normal atmospheric pressure
1 x 10⁵ N/m²
1 x 10⁵ Pa
Kilopascal
as numbers can be large, the kilo-pascal is also used
Volume
how much space something takes up
Si unit of volume
cubic meter (m³)
Gas & containers
volume of a sample of gas is same as container it is held in
Other ways volume is measured
cm³
litre (also known as dm³)
Pressure & volume
As pressure goes up, volume goes down
Pressure & temperature
as temperature (K) goes up, so does the pressure
Pressure & temperature limitation
only works when temp is on Kelvin scale
The Kinetic Theory of Gases - assumptions
- Gases made up of particles that are in continuous rapid, random motion, colliding w/ each other + walls of container
- No attractive or repulsive forces between particles of a gas
- Gas particles are so small + widely separated that total volume of all particles is negligible compared with space they occupy
- Collisions between particles are perfectly elastic, ie no overall loss of kinetic energy in these conditions
- Average kinetic energy of particles in a sample of a gas is proportional to temp measured on Kelvin scale
The Kinetic Theory of Gases - limitations
- contrary to assumption 2, there are forces of attraction between particles of a gas
eg. Van der Waals forces / Diople-dipole forces - contrary to assumption 3, it is not valid to say that total volume of gas is always negligible compared with the space that they occupy
- since these assumptions are not simply true, kinetic theory gases can only apply perfectly to what might be termed an ideal gas - no such gas exists
gases deviate most from ideal behaviour when:
- under high pressure (particles forced close together
- at low temperature (particles moving slowly)
- under these conditions, effect of inter-molecular fores becomes significant = volume of particles cannot be ignored when compared to volume in which they move
gases come close to ideal behaviour when particles are separated from each other
- low pressure
- higher temperatures
- majority of gases (under normal conditions) conform reasonably well to ideal behaviour
- more the case w/ non-polar particles bc Van der Waals forces are relatively weak
give 2 reasons why real gases depart from ideal behaviour
give 2 assumptions with limitations
eg. in an ideal gas, it is assumed that….
in real gases, ….
one mole
6 x 10²³
mass of one mole of an element
relative atomic mass in grams
counting atoms
use moles
Ideal gas law formula
pV = nRT
p = pressure (Pa) V = volume (m³) n = no. of moles R = universal gas constant T = temp (K)
why real gases deviate from ideal behaviour at high pressure and low temperatures
- molecules have non-negligible volume
- forces between molecules / molecules attract]repel one another
Calculating no. of moles
n = m/Mr
calculating mass in reaction
use n = m/Mr
calculating volume of something at s.t.p
remember 1at standard temp + pressure (s.t.p) one mole of any gas occupies 22.4 litres,
so just multiply 22.4 by the no. of moles of that something
calculating number of molecules produced in a reaction
multiply no. of moles by avogadro’s number (6x10²³)
1 mole of a substance has 6x10²³ molecules
give one reason why a real gas like ammonia deviates from ideal behaviour
ammonia has intermolecular forces between mlecules
equation of a state of an ideal gas
pV = nRT
p = Pa V = m³ n = moles R = universal gas constant T = Kelvin
1 litre in m³
1 litre = 0.001 m³
to find the relative molecular mass of a gas
find the mass for 1 mole…
- Find no of moles of gas and know/find the no. of grams of gas for that no. of moles
- turn it into 1 mole to find the no. of grams for 1 mole.
volatile liquid
a liquid with a low boiling point, or evaporates easily
relative molecular mass
the mass of a molecule relative to the mass of 1/12 mass of the carbon-12 isotope
experiment to determine relative molecular mass of a volatile liquid
- incl diagram
- describe procedure
how may pressure be measured
using a:
- barometer
- bourdon gauge
- barograph
- pressure sensor (not probe)
activation energy diagram
must know
what type of household product would you expect to find sodium hypochlorite
bleach / disinfectant
Robert Boyle facts
- Irish scientist
- born 1627
- son of the Earl of Cork
- made Boyle’s law
why carbon dioxide is more easily liquefied than helium
stronger intermolecular forces
how many moles of gas are present in a sample containing 1.8 x 10²⁴ atoms of chlorine at s.t.p
1: divide 1.8 x 10²⁴ by 2, as Cl is diatomic
2. divide by Avogadro’s number (1 mole = 6 x 10²³ particles)
how many atoms are present in 560 cm³ of ammonia at s.t.p
0.025 x 6 x 10²³ x 4
4, bc there are 4 atoms in ammonia (NH₃)
0.025 because
dm³ and litre
1 dm³ = 1 litre
suggest a way that further deterioration of a painting by this chem reaction could be prevented or delayed (bc of h2o)
keep it dry / low humidity / use waterproof varnish (coating)
decimal point vs sig figure
eg. give 0.00494 correct to one sig figure
sig figure is any number not 0, decimal point is to do with placement
0.005
note when using molar volume
ensure its in litres, eg. when turning volume to moles make sure volume is in litres before dividing by 22.4 or 24!!
complete and balance the equation:
C2H5OH + Na –>
C2H5ONa + H2
then balance it
“calculate total volume of the gaseous products”
Add up the volumes of the gaseous products at the end!!
Expressing pressure in terms of atmospheres
1 atmosphere = 1x10^5 Pa,
so when you get the answer (Eg. 139675.2 Pa), round it up (depending on how many decimal points they want it in) eg. 140000 Pa, then express in atm
-> 1.4 atm
Kp equil constant eg.
Kp = (Pₚᵣₒ𝒹ᵤ𝒸ₜ ₁)(Pₚᵣₒ𝒹ᵤ𝒸ₜ ₂)/(Pᵣₑₐ𝒸ₜₐₙₜ)
