definitions

Question 1

rate determining step

Answer 1

the slowest step in a reaction mechanism

Question 2

order of reaction

Answer 2

the power of the reactant’s concentration term in the experimentally-determined rate equation, rate=K[A]^m[B]^n

Question 3

standard enthalpy change of neutralisation

Answer 3

the enthalpy change when one mole of water is formed from the reaction of an acid and an alkali under standard conditions, 298K and 1 bar

NaOH(aq) +HCl(aq) –> NaCl(aq) + H2O(l)

Question 4

half life

Answer 4

time taken for the concentration of a reactant to be halved

Question 5

entropy

Answer 5

measure of disorder in a system

Question 6

ionisation energy

Answer 6

enthalpy change when one mole of electrons is removed from one mole of gaseous atoms

Al(g) –> Al+(g) + e-

Question 7

standard enthalpy change of combustion

Answer 7

enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions at 298K and 1 bar

C(s) + O2(g) –> CO2(g)

Question 8

electron affinity

Answer 8

enthalpy change when one mole of gaseous atoms accepts one mole of electrons

O(g) + e- –> O-(g)

Question 9

lattice energy

Answer 9

enthalpy change when one mole of solid ionic compound is formed from its constituent gaseous ions under standard conditions at 298K and 1 bar

Mg2+(g) + O2-(g) –> MgO(s)

Question 10

standard enthalpy change of atomisation

Answer 10

-of an element is the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state under standard conditions at 298K and 1 bar

Ca(s) –> Ca(g)

Question 11

bond dissociation energy

Answer 11

average enthalpy change when one mole of covalent bonds between atoms in gaseous molecules is broken

H2(g) –> 2H(g)

Question 12

standard enthalpy change of formation

Answer 12

enthalpy change which occurs when one mole of substance is formed from its constituent elements in their standard states at standard conditions, 298K and 1 bar

H2(g) + 1/2O2(g) –> H2O(l)

Question 13

standard enthalpy change of reaction

Answer 13

enthalpy change when molar quantities of reactants, as specified by the balanced chemical equation react to form products under standard conditions at 298K and 1 bar

Question 14

standard enthalpy change of solution

Answer 14

enthalpy change when one mole of substance is completely dissolved to give an infinitely dilute solution under standard conditions, so that no further enthalpy change takes place on adding more solvent

Question 15

standard enthalpy change of hydration

Answer 15

-of an ion is the enthalpy change when one mole of gaseous ions are hydrated under standard conditions at 298K and 1 bar

Na+(g) –> Na+(aq)

Question 16

activation energy

Answer 16

minimum amount of energy possessed by reactant particles for a reaction to take place

Question 17

rate constant

Answer 17

proportionality constant in the experimentally - determined rate equation, rate= K[A]^m[B]^n

Question 18

rate of reaction

Answer 18

change in concentration of reactant or product per unit time

Question 19

dynamic equilibrium

Answer 19

refers to the reversible process at equilibrium which the rate of the forward reaction is equal to the rate of the backward reaction