Topic 1: Stoichiometric Relationships

Question 1

element

Answer 1

A sample substance composed of a single type of atom

Question 2

isotope

Answer 2

Atoms of the same element, having the same no. of protons, but with differing no. of neutrons

Question 3

compound

Answer 3

A mixture of elements in which atoms of various elements chemically combine together in a fixed ratio

Question 4

vapor pressure

Answer 4

The pressure that a liquid’s gaseous form exerts in a closed environment

Question 5

Outline the liquid-vapour equilibrium

Answer 5

A liquid in an enclosed chamber will form a dynamic equilibrium with its own vapor:

• fast-moving particles in the liquid escape and become vapor
• slow-moving particles in the vapor becomes part of the liquid

Question 6

Effect of temperature on vapor pressure

Answer 6

• as temp. increases, average speed of particles increases

- so as temp. increases, equilibrium vapour pressure also increases

Question 7

Define the enthalpy of vaporisation

Answer 7

A measure of the energy change when 1 mol of liquid converts to gas at standard pressure

Question 8

What is the relationship between the boiling point of a liquid and the equilibrium of vapor pressure & atmospheric pressure?

Answer 8

The boiling point of a liquid is the temperature at which vapour pressure = atmospheric pressure

Elaboration: food in a pressure cooker is cooked faster because of the alteration in boiling point (70 degrees Celsius instead of 100)

Question 9

mole

Answer 9

The amount of substance containing the same number of atoms as in exactly 12g of the isotope C-12

Question 10

relative atomic mass

Answer 10

The average mass of an atom of the element, taking into account all the isotopes and their relative abundance, as compared to 1 atom of C-12

Question 11

relative molecular mass

Answer 11

The sum of the relative molecular mass of all the atoms in a molecule

Question 12

relative formula mass

Answer 12

The sum of the relative formula mass of all the atoms in one unit of an ionic compound

Question 13

Difference between molecule and formula

Answer 13

Molecule: refers to covalent compounds
Formula: refers to ionic compounds

Question 14

molecular formula

Answer 14

Gives the real number of atoms of the elements present in one molecule of the compound

Question 15

empirical formula

Answer 15

The simplest whole number ratio of the atoms of elements in one molecule

Question 16

Avogadro’s Law

Answer 16

an equal vol. of gases, both measured at the same temp. and pressure, contain an equal no. of particles.

v1/n1 = v2/n2

v: volume
n: no. of particles/moles

Question 17

ideal gas concept

Answer 17

• no attractive forces between gaseous particles
• KE of particles are directly proportional to temp
• follows the kinetic particle theory 100%

Question 18

when are real gases closest to the ideal gas concept?

Answer 18

when the temp is high and pressure is low

Question 19

how temperature affects real gases

Answer 19

the lower the temp. is, the slower molecules move —> the stronger the intermolecular forces

Question 20

how pressure affects real gases

Answer 20

the higher the pressure, the closer molecules are to each other —> the stronger the intermolecular attractive bonds

Question 21

ideal gas equation

Answer 21

PV = nRT

P: pressure
V: volume
n: no. of moles
R: ideal gas constant
T: temp.

Question 22

Boyle’s law

Answer 22

at constant temp , pressure is inversely proportional to volume

P1V1 = P2V2

Question 23

gas law

Answer 23

P1V1 / T1 = P2V2 / T2
OR
PV/T = a constant

Question 24

dilution of solutions equation

Answer 24

C/V = a constant
OR
c1v1 = c2v2
c = conc
V = vol

Question 25

solutions and concentration equation

Answer 25

conc. of soln x vol = amount of solute

Question 26

mole equations

Answer 26

no. of moles = no. of particles / Avogadro’s constant
no. of moles = mass / molar mass
no. of moles = concentration x volume

Question 27

law of conservation

Answer 27

matter can neither be created nor destroyed, it can only be changed from one form to another

Question 28

how to calculate yield from reaction equations

Answer 28

1. Obtain the stoichiometric values of the reaction (molar coefficients of each compound)
2. Use mole equations to find the limiting reagent
3. You can find the max yield from there

Question 29

percentage yield formula

Answer 29

(experimental yield / theoretical yield) x 100

Question 30

back-titration

Answer 30

• technique analysing excess acid/alkali after rxn is complete
• indirectly measures amount of limiting reactant

Question 31

gas and molar volume relationship

Answer 31

• all gases under same conditions have same molar volume

e. g. STP/RTP

Question 32

temperature

Answer 32

average energy of particles in a system

Question 32

relationship between pressure and temp of gas

Answer 32

P/T = a constant
OR
P1/T1 = P2/T2

Question 33

Charles’ Law

Answer 33

• volume is directly proportional to absolute temperature
• V/T = a constant
  V1/T1 = V2/T2

Question 35

why is beer stored in cold places?

Answer 35

• they can burst!

the higher the temp, the higher the pressure.