Organic: Alkanes

Question 1

explain properties of alkanes

Answer 1

general formula- CnH2n+2
saturated single carbon chain
as no of c atoms increase bp increases due to increase of VdWs so more energy to ocercome

Question 2

what factors effect boiling points

Answer 2

carbon chain length- more vdw forces
branches- decreases bp as more branches increases, due to more points of contact

Question 3

explain the types of cracking of alkanes

Answer 3

thermal cracking- alkanes heated to high temperature, producing high percentage of low Mr alkenes, goof for polymer making
Catalytic cracking- using a catalyst (usually zeolites) and lower temperatures + lower pressures, producing many branched alkanes used for petrols, cycloalkanes and aromatics, better for fuels

Question 4

uses and issues of alkanes

Answer 4

alkanes are used for fuels so combustion occurs incomplete or complete
These gaseous pollutants from internal combustion engines such as SO2, SO3, when burnt can be removed using catalytic converters honeycomb to provide a large surface area
learn equations:
2CO + 2NO → 2CO2 + N2

2CO + 2NO → 2CO2 + N2

Question 5

explain why sulfur dioxide can be removed from flue gases using calcium oxide or calcium carbonate.

Answer 5

sulfur impurities lead to acid rain by forming H2SO4. impurities can be removed by flue gas desulfuration

Question 6

Explain the process of Free-radical substitution of methane to form chloromethane

Answer 6

initiation- Cl2—> 2Cl. (radical, homolytic fission, pressence of UV light)
propagation- CH4 + Cl. —> C.H3 (methyl radical) + HCL
C.H3 +Cl2 —> CH3Cl (chloroethane) + Cl. (chloride radical)
termination- C.H3 + C.H3 —> C2H6 ethane
C.H3 + Cl. —> CH3Cl (chloroethane)
overall reaction
Cl2 + CH4 —> CH3Cl + HCL