CI

Question 1

nitrogen gas is unreactive because

Answer 1

it contains a triple bond, high bond enthalpy, therefore large amount of energy required to break triple bond

Question 2

bonding in ammonia

Answer 2

chemical formula NH3, sigma bonds between nitrogen and each hydrogen, lone pair on hydrogen (therefore tetrahedral shape)

Question 3

ammonium ions

Answer 3

lone pair in ammonia forms dative covalent bond with a proton

Question 4

nitrate III

Answer 4

NO2-

charge is delocalised over the two N-O bonds

Question 5

nitrate V

Answer 5

NO3-

dative covalent bond to one of the hydrogen atoms

Question 6

solubility of nitrates

Answer 6

very soluble in water

Question 7

nitrification

Answer 7

oxidation of ammonium ions in the soil to form nitrates by nitrifying bacteria

3/2(O2) + NH4+&raquo_space; NO2- + H20 + 2H+
NO2- + 1/2(O2)&raquo_space; NO3-

Question 8

test for nitrate V

Answer 8

NaOH and Devarda’s alloy added to test solution
gently heated
aluminium acts as reducing agent
if nitrate V present, ammonia gtas evolved

Question 9

effect of ammonia gas on damp litmus paper

Answer 9

turns from red to blue

Question 10

testing for ammonium ions

Answer 10

NaOH added to test solution
gently heated
if ammonium ions are present, ammonia gas is evolved

Question 11

effect of increase in pressure on equilibrium and Kc

Answer 11

equilibrium shifts to side producing fewest moles of gas to counteract change in pressure
Kc remains unchanged

Question 12

effect of catalyst on position of equilibrium and Kc

Answer 12

no effect on either

Question 13

rate of reaction

Answer 13

rate of converting reactants to products

can be expressed as rate of reactant used or rate of product formed

Question 14

general rate equation

Answer 14

rate = k [A]^m [B]^n

m = order of reaction with respect to A
n = order of reaction with respect to B

Question 15

overall order of reaction

Answer 15

order of reaction with respect to A + order of reaction with respect to B

( m + n )

Question 16

units of overall order of reaction

Answer 16

zero order = moldm-3 s-1
first order = s-1
second order = dm3 mol-1 s-1

Question 17

finding order with respect to a reactant

Answer 17

carry out the reaction several times, varying concentration of 1 reactant
use tangent to each progress curve to calculate initial rate at each concentration
plot initial rate against concentration to determine order with respect to reactant

Question 18

using half life to determine order of reaction with respect to reactant

Answer 18

plot progress curve (reactant used/product formed against time)
calculate half lives
if constant then reaction is first order

Question 19

rate equation can tell you:

Answer 19

gives info about the slowest step in the reaction (rate determining step)
indicates what substances in the reaction are and aren’t involved in the rate determining step
order of reaction for each substance indicates relative number of moles of each substance involved in the rate determining step

Question 20

substance with zero order in rate equation

Answer 20

not involved in rate determining step

Question 21

why are some steps slow?

Answer 21

steps have different Ea (activation enthalpy)

large Ea means only a small number of species have enough energy to react and form products