chem definitions

Question 1

isotopes

Answer 1

are atoms of the same element with different numbers of neutrons and different masses

Question 2

relative isotopic mass

Answer 2

is the mass of an isotope relative to 1/12 th of the mass of an atom of carbon - 12

Question 3

relative atomic mass

Answer 3

is the weighted mean mass of an element relative to 1/12 th of the mass of an atom of carbon - 12

Question 4

avogadro’s constant

Answer 4

6.02 x 10^23

Question 5

molar mass

Answer 5

is the mass per mole of a substance (g mol^-1)

Question 6

molecular formulae

Answer 6

the number of atoms of each element in a molecule

Question 7

empirical formulae

Answer 7

is the simplest whole-number ration of atoms of each element in a compound

Question 8

relative molecular mass

Answer 8

compares the mass of a molecule with the mass of an atom of carbon-12

Question 9

relative formula mass

Answer 9

compares the mass of a formula unit with the mass of an atom of carbon-12

Question 10

molar gas volume

Answer 10

is the volume per mole of gas molecules at a stated temperature and pressure

Question 11

room temperature and pressure (RTP)

Answer 11

25 degrees Celsius / 298 K

101 kPa / 1 atm pressure

Question 12

ideal gas equation

Answer 12

pV = nRT
pressure (Pa)
volume (m^3)
amount of gas molecules (mol)
R = gas constant (8.31 J mol^-1 K^-1)
temperature (K)

Question 13

celcius to kelvin

Answer 13

+ 273

Question 14

kPa to Pa

Answer 14

x 10^3

Question 15

percentage yield

Answer 15

= (actual yield) / (theoretical yield)

x100 for percentage

Question 16

atom economy

Answer 16

is a measure of how well atoms have been utilised

= (sum of molar masses of desired products) / (sum of molar masses of all products)
x100 for percentage

Question 17

strong acids

Answer 17

e.g HCL

releases all its hydrogen atoms into solution as H+ ions completely dissociates in aqueous solutions

Question 18

weak acids

Answer 18

e.g ethanoic acid (CH3COOH)
only releases a small proportion of its available hydrogen atoms into solution as H+ ions.
partially dissociates in aqueous solution

Question 19

alkali

Answer 19

is a base that dissolves in water releasing hydroxide ions (OH-) into the solution

Question 20

acid + alkali

Answer 20

= salt + water

Question 21

ionic bonding

Answer 21

is the electrostatic attraction between positive and negative ions.
it holds together cations and anions in ionic compounds

Question 22

properties of ionic compounds

Answer 22

have high melting and boiling points
tend to dissolve in polar solvents: water
conduct electricity only in liquid state or in aqueous solution

Question 23

covalent bonding

Answer 23

is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 24

dative covalent bond

Answer 24

is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only.

Question 25

electronegativity

Answer 25

the attraction of a bonded atom for the pair of electrons in a covalent bond

Question 26

intermolecular forces

Answer 26

are weak interactions between dipoles of different molecules
split into 3 categories: induced dipole-dipole interactions, permanent dipole-dipole interactions
hydrogen bonding

Question 27

induced dipole-dipole interactions (london forces)

Answer 27

are weak intermolecular forces that exist between all molecules

Question 28

permanent dipole-dipole interactions

Answer 28

act between the permanent dipoles in different polar molecules

Question 29

simple molecular substance

Answer 29

= is made up of simple molecules - small units containing a definite number of atoms with a definite molecular formula

Question 30

ionisation energy

Answer 30

measures how easily an atom loses electrons to form positive ions

Question 31

first ionisation energy

Answer 31

is the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 32

disproportionation

Answer 32

is a redox reaction in which the same element is both oxidised and reduced

Question 33

enthalpy

Answer 33

is a measure of the heat energy in a chemical system

Question 34

enthalpy change

Answer 34

= enthalpy of products - enthalpy of reactants

Question 35

activation energy

Answer 35

the energy input required to break bonds acts as an energy barrier to the reaction
is the minimum energy required for a reaction to take place

Question 36

standard enthalpy change of reaction

Answer 36

is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states

Question 37

enthalpy change of formation

Answer 37

is the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

Question 38

standard enthalpy change of combustion

Answer 38

is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states

Question 39

standard enthalpy change of neutralisation

Answer 39

is the energy change that accompanies the reaction of an acid by a base to form one mole of h20(l), under standard conditions, with all reactants and products in their standard states

Question 40

specific heat capacity

water?

Answer 40

is the energy required to raise the temperature of 1g of a substance by 1K
water = 4.18 J g^-1 K^-1

Question 41

calculating energy change formulae

Answer 41

q = mcT

q = heat energy
m = mass that changes temperature
c = specific heat capacity
T = temperature change