past mistakes

Question 1

what effect does an increase in temp have on Kc/Kp?

Answer 1

• if forwards reaction is exothermic, an increase in temp shifts eq to left
• decreases the ratio of products:reactants, so Kc/Kp decreases
• if forwards reaction is endothermic, an increase in temp shifts eq to right
• increases the ratio of products:reactants and so Kc/Kp increases

Question 2

what effect does pressure have on Kc/Kp?

Answer 2

• no effect on Kc, as gases aren’t involved
• no effect on Kp, as a change in pressure involves a shift in the equilbrium, which restores the value of Kp

Question 3

which redox half equation takes place at the positive electrode?

Answer 3

reduction

Question 4

which redox half equation takes place at the negative electrode?

Answer 4

oxidation

Question 5

why is it hard to predict if enthalpy change of solution becomes more or less exothermic down the group, from MgF2 to MgI2?

Answer 5

• halide ions get larger as you go down the group
• lattice enthalpy is less exothermic down the group (attractive forces between the ions are weaker)
• enthalpy of hydration is less exothermic down the group (reduced strength of attractions between ions and water molecules)
• difficult to predict whether lattice enthalpy or hydration has a larger effect

Question 6

why is the enthalpy change of solution of KF less exothermic than RbF?

Answer 6

• K ion is smaller than Rb ion
• so lattice enthalpy of KF is more exothermic than RbF
• hydration of K ion is more exothermic than Rb ion
• enthalpy of solution is affected more by lattice enthalpy than hydration

Question 7

rates of hydrolysis of haloalkanes

Answer 7

• C-Cl bond is stronger than C-Br bond
• so C-Cl reacts slower/ slower rate of hydrolysis
  (C-I bond is weaker than C-F bond so faster rate of hydrolysis)
• the weaker the C-halogen bond, the faster the rate (of hydrolysis)

Question 8

what is an elimination reaction?

Answer 8

• a reaction which involves the removal or a small molecule from a larger one

Question 9

what is an addition reaction?

Answer 9

• two reactants join together to form one product

Question 10

what is a substitution reaction?

Answer 10

• two reactants where one atom or group of atoms replaces another set of atoms

Question 11

what are the benefits of using a catalyst, for energy demand and the environment?

Answer 11

• activation energy reduced, so reactions take place at lower temps, less energy required, lower costs
• different reactions are possible with better atom economy/less waste
• reduced CO2 emissions/ less fossil fuels burned

Question 12

what is a nucleophile?

Answer 12

electron pair donor

Question 13

what is an electrophile?

Answer 13

electron pair acceptor

Question 14

electrophilic addition

mechanisms we need to know

Answer 14

• alkenes + halogens/ hydrogen halides

Question 15

electrophilic substitution

mechanisms we need to know

Answer 15

• halogenation of benzene
• nitration of benzene

Question 16

nucleophilic addition

mechanisms we need to know

Answer 16

• carbonyl and KCN
• reduction of carbonyls

Question 17

nucleophilic substitution

mechanisms we need to know

Answer 17

• haloalkanes + NaOH

Question 18

when testing for ions in a SOLID mixture, what must you do to the sample before taking any tests?

Answer 18

• sample is stirred with water
• and mixture is filtered out
• anions (positive) are tested on the filtrate
• cations (negative) are tested on the residue