1.3 reacting masses and volumes

Question 1

kinetic molecular theory of gases (5 postulates)

Answer 1

1. The particles in a gas are in constant, random, straight-line motion.
2. There are negligible forces of attraction (intermolecular forces) between the particles.
3. Collisions between particles or with the walls of the container are perfectly elastic (no energy is lost).
4. The distance between the particles is much greater than the size of the particles, therefore, gas particles have negligible volume.
5. The kinetic energy of the particles in a gas is directly proportional to the absolute temperature (in kelvin

Question 2

avogaddro’s law

Answer 2

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.

Question 3

reacting gas volumes

Answer 3

volume ratio of reacting gases = molar ratio

Question 4

molar volume of a gas

Answer 4

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)

Question 5

ideal gases

Answer 5

An ideal gas is a gas that exhibits the five postulates of the kinetic molecular theory, as well as obeying the gas laws.

Question 6

gas laws

Answer 6

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.

Question 7

boyle’s law (proposition+eqn)

Answer 7

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

Question 8

how to find from celcius

Answer 8

K = celcius +273.15

Question 9

absolute zero

Answer 9

• 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.

Question 10

charles’ law

Answer 10

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

Question 11

gay-lussac’s law

Answer 11

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.

Question 12

combined gas law

Answer 12

TEMP AKLW CALCULATE IN KELVIN
PV/T = k

or P1V1/T1 = P2V2/T2

combined w arrhenius
PV=nRT

Question 13

ideal gas eqn (given in formula booklet)

Answer 13

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).

Question 14

what can you find using ideal gas eqn

Answer 14

amount (in mol)
n = PV/RT

molar mass (M)
M=mRT/PV

Question 15

what assumptions made about ideal gas isn’t made with real gas? (assumption+c2conditions)

Answer 15

1. At very high pressure the gas particles are closer together. Under these conditions, the actual volume of the particles becomes significant.
2. 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.

Question 16

real gases

Answer 16

deviate from ideal gas behaviour under two conditions: at high pressures and low temperatures.

Question 17

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

Question 18

gases that show most ideal behaviour

Answer 18

low mr and weakest intermolecular forces
(helium)

Question 19

gases that are least ideal (deviate the most from ideal behaviour)

Answer 19

• gases where bonds are permanently polarised
• or higher mr

Question 20

concentration

Answer 20

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)

Question 21

concentration in ppm

Answer 21

concentration (ppm) = mass of solute (g)/mass of solution (g) x 10^6

Question 22

standard solutions (def + 4 properties)

Answer 22

solution w an accurately known concentration

High purity (99.9 %).
High molar mass.
Low reactivity.
Does not change composition in contact with air.

Question 23

secondary standard solution

Answer 23

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.

Question 24

serial dilution

Answer 24

involves diluting a stock solution multiple times, usually by the same factor, which results in an exponential decrease in concentration.