1.3 reacting masses and volumes Flashcards
kinetic molecular theory of gases (5 postulates)
- The particles in a gas are in constant, random, straight-line motion.
- There are negligible forces of attraction (intermolecular forces) between the particles.
- Collisions between particles or with the walls of the container are perfectly elastic (no energy is lost).
- The distance between the particles is much greater than the size of the particles, therefore, gas particles have negligible volume.
- The kinetic energy of the particles in a gas is directly proportional to the absolute temperature (in kelvin
avogaddro’s law
states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
This finding is very important, as it means that we can directly relate the volume of any gas to the amount (in mol) of the gas.
reacting gas volumes
volume ratio of reacting gases = molar ratio
molar volume of a gas
The volume occupied by one mole of a gas at conditions of standard temperature and pressure (STP) is the molar volume of a gas.
This states that one mole of a gas at STP occupies a volume of 22.7 dm3 (22700 cm3 or 0.0227 m3).
amount in mol(n) = volume(dm3)/molar volume(22.7dm3)
ideal gases
An ideal gas is a gas that exhibits the five postulates of the kinetic molecular theory, as well as obeying the gas laws.
gas laws
The gas laws (Boyle’s Law, Charles’ Law, and Gay-Lussac’s Law) describe the behavior of a gas when subjected to changes in temperature and pressure.
boyle’s law (proposition+eqn)
states that at constant temperature the pressure and volume of a fixed mass of an ideal gas are inversely proportional to each other (Figure 1).
So, if the pressure of a fixed mass of gas at constant temperature is doubled, the volume halves.
PV=k
graph: P against 1/V is straight line
P against V is curve with x=0 and y=0 asymptotes
how to find from celcius
K = celcius +273.15
absolute zero
- Absolute zero (0 K) is the lowest possible temperature on the Kelvin scale.
- In a Maxwell-Boltzmann curve, it is the origin of the x-axis of the distribution.
- At absolute zero the motion of particles is minimal. - At this point, a substance has no transferable heat energy.
- Also, at this temperature, an ideal gas at constant pressure would reach zero volume.
charles’ law
states that at constant pressure the volume of a fixed mass of an ideal gas is directly proportional to its absolute temperature (in kelvin). This means that if the absolute temperature of a fixed mass of an ideal gas is doubled, the volume of the gas will also double. Charles’ Law can be represented in equation form as:
V ∝ T or V/T = k
graph axes:
x-temp
y-volume
gay-lussac’s law
states that at constant volume the pressure of a fixed mass of an ideal gas is directly proportional to its absolute temperature (in kelvin).
This means that if the absolute temperature of a fixed mass of an ideal gas is doubled, the pressure of the gas will also double.
Gay-Lussac’s law can be represented in equation form as:
P ∝ T or P/T = k
where k is a constant.
combined gas law
TEMP AKLW CALCULATE IN KELVIN
PV/T = k
or P1V1/T1 = P2V2/T2
combined w arrhenius
PV=nRT
ideal gas eqn (given in formula booklet)
PV = nRT
P is the pressure in pascals (Pa),
V is the volume in m3,
n is the amount of gas (in mol),
R is the universal gas constant (8.314 J K–1 mol-1),
T is the absolute temperature (in kelvin).
what can you find using ideal gas eqn
amount (in mol)
n = PV/RT
molar mass (M)
M=mRT/PV
what assumptions made about ideal gas isn’t made with real gas? (assumption+c2conditions)
- At very high pressure the gas particles are closer together. Under these conditions, the actual volume of the particles becomes significant.
- At low temperatures, the particles move less rapidly (have lower average kinetic energy). This means that there is a greater opportunity for intermolecular forces between the particles to have an effect.
real gases
deviate from ideal gas behaviour under two conditions: at high pressures and low temperatures.
Using the conditions of temperature and pressure at STP, the product of PV/RT for an ideal gas is always equal to one.
n = PV/RT
at high pressure and low temp, n deviate from 1
gases that show most ideal behaviour
low mr and weakest intermolecular forces
(helium)
gases that are least ideal (deviate the most from ideal behaviour)
- gases where bonds are permanently polarised
- or higher mr
concentration
is the amount (in mol) or mass (in g) of solute per volume of solution. Units of concentration include mol dm-3, g dm-3 or parts per million (ppm).
conc (moldm-3) = amt of solute(mol)/volume of solution (dm3)
concentration in ppm
concentration (ppm) = mass of solute (g)/mass of solution (g) x 10^6
standard solutions (def + 4 properties)
solution w an accurately known concentration
High purity (99.9 %).
High molar mass.
Low reactivity.
Does not change composition in contact with air.
secondary standard solution
is a solution that has been standardised against a primary standard solution. For example, a sodium hydroxide solution can be standardised against a primary standard solution, and can then be used as a secondary standard solution.
serial dilution
involves diluting a stock solution multiple times, usually by the same factor, which results in an exponential decrease in concentration.
