Alkanes

Question 1

Define saturated, hydrocarbons and state the general formula for alkanes

Answer 1

Saturated-Molecules containing a single bond only
Hydrocarbons- molecules containing carbon and hydrogen only
CnH2n+2

Question 2

Explain the effect of chain length on boiling point

Answer 2

Larger molecules- induced dipole dipoles between molecules. Strength of attractions increases with size of atoms and number of electrons. The longer the chain the more electrons and the bigger the molecule.
More branches= more surface contact between molecules of pentane so the IDD attraction is stronger

Question 3

Fraction definition. State the process of distillation

Answer 3

Def- a group of hydrocarbons with similar boiling points.
Crude oil is heated and vaporised as it enters the column at the bottom. The mixture of hydrocarbons have different boiling points. Their boiling points depend on chain length and branching. It is hotter at the bottom. Larger or longer molecules condense first at the bottom and collect.

Question 4

Cracking

Answer 4

Purpose: to produce more useful, shorter chain molecules that are in higher demand.
Thermal cracking uses 700-1200k temp and 7000 kPA pressure
Cracking equation example: C16H34 cracked into C8H18 ethene and propane.
C16H34–> C8H18 + C2H4 + 2C3H6
Catalytic cracking: uses 720 kelvin, 200kpa, zeolite catalyst