chapter 12 - alkanes

Question 1

alkanes

Answer 1

a homologous series of saturated hydrocarbons that share the general formula CnH2n+2

Question 2

boiling point of alkanes

Answer 2

the longer the alkane chain, the more points of contact there are and the more London dispersion forces there are so the higher the boiling point

Question 3

effect of branching on boiling point

Answer 3

the more branches there are, the less packed it will be and the less points of contact there would be so the boiling point decreases

Question 4

alkane properties

Answer 4

• non-polar so only London forces are present - only soluble in non-polar solvents

Question 5

alkane reactivity

Answer 5

very low reactivity due to the σ-bonds having: - a very low polarity - a high bond enthalpy

Question 6

combustion reaction

Answer 6

an exothermic reaction that occurs when a fuel is oxidised by oxygen

Question 7

complete combustion

Answer 7

occurs when there is excess oxygen and will form carbon dioxide and water eg CH4 + 2O2 → CO2 + 2H2O

Question 8

incomplete combustion

Answer 8

occurs when there is limited oxygen and will form carbon monoxide and water eg CH4 + 1½O2 → CO + 2H2O and CH4 + O2 → C + 2H2O

Question 9

intiation (radical substitution)

Answer 9

diatomic haolgen molecules can be split into halogen radicals by UV raditaion the pair of electrons in the bond are split up evenly to form halogen radicals by homolytic fission

Question 10

propagation (radical substitution)

Answer 10

a series of reactions help to maintain the concentration of halogen radicals
eg step 1: CH4 + Cl* → HCl + *CH3
step 2: CH3 + Cl2 → CH3Cl + Cl

Question 11

termination (radical substitution)

Answer 11

two radicals react with each other to form a covalent bond