3.2 Alkanes Flashcards
(16 cards)
General formula of alkanes
CnH2n+2
What does it mean by alkanes being saturated hydrocarbons?
They do not contain a c=c bond
Made of carbon and hydrogen atoms only
How are alkanes formed from crude oil?
Fractional distillation involving the breaking of van der waal’s forces
How does fractional distillation work?
Hot crude oil (containing a mixture of diff alkanes) is pumped into the fractionating column
Moving up the column the temperature decreases
If a fraction consists of low Tb molecules it turns into a vapour in the column and moves up until it reaches a compartment where T<Tb
-it condenses to a liquid and can be tapped off
High Tb fractions remain as liquids and move down the column
Molecules at the top (C1-C4) have low Tbs. Why?
They have a low surfaces area/very few e’s
Therefore weaker van der waal’s between molecules
Molecules at the bottom have high Tbs. Why?
They are large so have a large surface area/lots of e’s
Therefore many van der waal’s between molecules
Main economic reasons alkanes are cracked
To produce products in high demand
So supply meets demand
Conditions for thermal cracking and what it produces
long chain hydrocarbons producing a high percentage of alkenes that can be used as chemical feedstock
High temperature and a high pressure
Conditions of catalytic cracking and what it produces
long chain hydrocarbons to shorter alkanes that can be used as fuels
High temperature and average pressure and zeolite catalyst
Diff between complete and incomplete combustion
same-release of energy
complete- excess of oxygen and alkane- carbon dioxide and water
incomplete- limited oxygen and alkane- carbon monoxide/carbon and water
Why is the release of CO dangerous?
it is toxic
causes asphyxia (suffocation)
stops oxygen and carbon dioxide from binding to haemoglobin as bond between CO and Hb is stronger
Why is the release of C dangerous
black deposit
forms photochemical smog
which is carcinogenic- causes lung cancer
Why is the release of sulfur dioxide dangerous?
it reacts with water to form acid rain (sulfuric (IV) acid) H2SO3
Also causes breathing difficulties-choking gas
What process removes S from crude oil?
Flue gas desulfuristation
-neutralisation reaction between sulfur dioxide and calcium oxide producing calcium sulfate
Why is the release of nitrogen dioxide dangerous?
-formed by very high temperatures in a combustion engine
Nitrogen monoxide and nitrogen dioxide are both toxic gases
How do catalytic converters work?
(very expensive)
mixture of Pt/Pd/Rh
put on a ceramic support- honeycombe structure
increases SA
forms nitrogen (harmless)
