Alkanes

Question 1

what are structural isomers/

Answer 1

molecules with the same molecular formula but a different structural formula

Question 2

what shape are all alkanes and why?

Answer 2

tetrahedral- they have 4 bonded pairs of electrons and no lone pairs

Question 3

how does boiling point of alkanes change with branching?

Answer 3

more branches = fewer points of contact= weaker IDD interaction= lower bpt

Question 4

write an equation for combustion of C2H6 with excess o2

Answer 4

C2H6 + 3.5O2 -> 2CO2 + 3H20

Question 5

write an equation for combustion of C2H6 with limited O2, forming a toxic gas

Answer 5

C2H6 + 2.5 O2 -> 2CO + 3H20

Question 6

write an equation for combustion of C2H6 with limited O2 forming a black solid

Answer 6

C2H6 + 1.5 O2 -> 2C + 3H2O

Question 7

what is a sigma bond?

Answer 7

head on overlap of 2 atomic orbitals directly in a line between the 2 bonded atoms

Question 8

what condition is necessary for an alkane to react with a halogen?

Answer 8

uv light

Question 9

give the overall equation for the reaction between propane and bromine to form bromopropane

Answer 9

C3H8 + Br2 -> C3H7Br + HBr

Question 10

what is a radical?

Answer 10

a species with an unpaired electron

Question 11

what type of bond breaking is shown in radical substitution?

Answer 11

homolytic fission- a covalent bond breaking with one of the bonded electrons going to each atom forming 2 radicals

Question 12

give the full mechanism for the reaction between methane and chlorine + name.

Answer 12

name: radical substitution
initiation: Cl2 -> 2Cl. (.= radical)
propagation: Cl. + CH4 -> C.H3 + HCl
C.H3 + Cl2 -> CH3Cl + Cl.
termination:
Cl. + Cl. -> Cl2
Cl. + C.H3 -> CH3Cl
C.H3 + C.H3 -> C2H6

Question 13

give 2 problems with radical substitution

Answer 13

1) further substitution: CH3Cl could react with CL. again multiple times, and hydrogens could keep getting substituted for chlorine.
2) mixture of isomers formed eg:
C4H10 + Cl2 -> CH3CH2CH2CH2Cl or CH3CH(Cl)CH2CH3