Chemistry
homologous series
family of organic compounds with the same general formula, similar chemical properties and successive members differing by CH2
structural isomer
compounds that have the same molecular formula but different structural formulas
alaphatic hydrocarbons
consist of straight/branched chains of carbon atoms/rings of carbon atoms other than those that contain a special benzene ring
aromatic hydocarbons
contain a benzene ring in their molecule
fractional distillation
a process used to seperate crude oil into a number of useful mixtures called fractions
how does fractional distillation work in relation to crude oil
the crude oil is heated and the various substances are seperated based on their boiling points
use of refinery gas
cooking
use of naptha
medicine/plastics
use of kerosene
central heating/air craft fuel
name and give use of residue fraction
bitumen, tarmac/roofing
cracking
breaking down of large hydrocarbons into smaller ones using a catalyst
auto-ignition
premature combustion of the petrol-air mixture in an internal coombustion engine
knocking
premature combustion of the petrol-air mixture in an internal coombustion engine
the octane number
the measure of the tendancy of a fuel to resist knocking
e.g of octane number of 100
2,2,4-trimethylpentane
e.g of octane number of 0
heptane
isomerisation
changing a straight chained compound into a branched chain
dehydrocyclisation
using catalysts to change straight chain compounds into cyclic structures
disadvantage of hydrogen as a fuel
forms an explosive mixture with air
blue hydrogen
steam reforming of natural gas
CH4 + H20 ---> 3H2 + CO
green hydrogen
electrolysis of water
H2O ---> H2 + 1/2 O2
exothermic reactions
energy change=negative
energy is released
bonds form
endothemic reactions
energy change=positive
energy's taken in
breaks bonds
bond energy
the amount of energy in kilojules needed to break one mole of bonds the same type, all species being in a gaseous state
hazards of CH4(methane)
death by suffocation through slurry pits
produces explosive mixture with air in coal mines
heat of reaction
🔺H
the heat in kilojules released or absored when the number of moles of reactants indicated in the balanced equation describing the reaction react completley
to calculate 🔺H
(m)(c)(🔺T)
____________
n
m= mass of liquid heated by reaction (KG)
c= specific heat capacity of liquid (4.2)
🔺T= rise in temp (kelvin)
n= number of moles
heat of combustion
the heat change in kilojules when one mole of the substance is fully burned in excess oxygen
heat of formation
🔺Hf
the heat change in kilojules when one substance is formed from its elements in their standard state
law of conservtin of energy
states that energy cannot be created or destroyed, only changed from one form to another
Hess's law
states that the heat change of a reaction depends only on the initial and final stages of the reaction and is independant of the route by which the reaction may occur