Fuels + Heats of Reactions - Chp 21 nf

Organic chemistry

is the study of the compounds of carbon

Hydrocarbon

is a compound that contains carbon and hydrogen only

Fossil fuels

fuels that were formed from the remains of plants and animals that lives millions of years agp

Saturated compound

is one in which there are only single bonds between the carbon atoms in the molecule

What are the prefixes for a carbon chain length from 1-10?

meth- 1 carbon

eth- 2 carbons

prop - 3 carbons

but- 4 carbons

pent - 5 carbons

hex- 6 carbons

hept- 7 carbons

oct- 8 carbons

non- 9 carbons

dec- 10 carbons

What is the suffix for the Alkane family?

-ane

What is the suffix for the Alkene family?

-ene

What is the suffix for the Alkyne family?

-yne

What is the suffix for the Alcohol family?

-anol

What is the functional group for the Alkane family?

What is the functional group for the Alkene family?

What is the functional group for the Alkyne family?

What is the functional group for the Alcohol family?

What is the general term of the Alkane family?

C_nH_2n+2

What is the general term of the Alkene family?

C_nH_2n

What is the general term of the Alkyne family?

C_nH_2n-2

What is an Alkyl group?

a type of side chain, substituent group, or branch consisting of an alkane from which a hydrogen atom is removed, these include; methyl CH₃, ethyl C₂H₅ and propyl C₃H₇

What is paraffin oil?

• paraffin oil is another name for kerosene, which is a commonly used fuel for central heating

• paraffin is the old name for alkanes, meaning that they have little reactivity

• paraffin oil consists mainly of alkanes, hence its name

Write an equation for the combustion of alkanes in excess oxygen:

alkane + O₂ → CO₂ + H₂O + heat

Homologous series

is defined as:

• a series of compounds of similar chemical properties
• showing gradations in physical properties
• having a general formula for its members
• each member having a similar method of preparation
• each member differing from the previous member by a (CH₂) unit

Explain the gradation of physical properties of the Alkanes and Alkenes

• the first few 3-4 are gases, the next 11-12 are liquids and the rest are waxy solids

• as the molecules increase in size, the Van der Waal’s forces between them also increase, due to the greater number of electrons in the electron clouds

• therefore the bigger the molecule, the stronger the intermolecular forces between them, creating a more solid compound

Draw and name the 3 structural isomers of butene:

Structural isomers

are compounds with the same molecular formula but different structural formulas

Why is ethene so important?

it is the starting material from which other substances, particularly plastics, are made

is also produced naturally by fruits as they ripen

When is a carbon described as being planar?

when there is a double or triple bond between carbons

When is a carbon described as being tetrahedral?

when there is a single bond between carbons

Write a balanced equation for the formation of ethene?

C₂H₅OH —Al₂O₃→C₂H₄ + H₂O

Key steps + observations in the procedure for the preparation of ethene:

1. some ethanol is poured into a boiling tube, and glass wool is added to soak up the ethanol and holds it in place at the end of the boiling tube

2. a small heap of aluminium oxide (alumina) is place midway along the boiling tube

3. the aluminium oxide is gently heated by the Bunsen burner, the ethanol is not heated directly as it would vaporise and pass over the aluminium oxide too quickly without being dehydrated to form ethene

4. bubbles of displaced air from the apparatus are allowed to escape for a short time before 5 test tube and a glass jar of ethene are collected

5. once finished, the apparatus is raised so that the delivery tube is no longer in the water, and only then is the Bunsen burner turned off; this prevents suck back

What safety precautions are taken when preparing ethene?

• stopper on the boiling tube must be air tight, and the Bunsen burner must not be allowed near the mouth of the boiling tube as any gas that escapes is flammable

• suck back occurs when the Bunsen burner is turned off before the delivery tube is removed from the water

  • the alcohol vapour in the boiling tube cools, creating a vacuum, and the water is sucked back to fill the space

  • the cold water can cause the hot boiling tube to crack or shatter

  • to avoid suck back, raise the apparatus in order to remove the delivery tube from the water before turning off the Bunsen

Describe the tests on ethene?

physical properties

• it is observed that ethene is a colourless gas with a sweetish smell

• collected over water, therefore it must be insoluble in water otherwise it would have dissolved; it is only soluble in organic solvents such as cyclohexane and chloroform

combustion

• stopper is removed from a test tube and a lit wax taper is held at the mouth of the test tube

  • a yellow-luminous, slightly smoky flame is observed

• when gas has stopped burning some limewater is added to the test tube, which is then stoppered and shaken

  • limewater turns milky due to the production of CO₂

tests for unsaturation

• bromine water is added to a test tube of ethene, which is stoppered and shaken

  • colour change from yellow-orange to colourless is observed

  • bromine bonds with the very reactive alkene to form a new colourless compound

• acidified potassium permanganate is added to a test tube of ethene, which is stoppered and shaken

  • colour change from purple to colourless is observed

Write an equation for the reaction when ethene burns in air:

C₂H₄ + 3O₂ → 2CO₂ + 2H₂O

Write an equation for the reaction between limewater and carbon dioxide:

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Applications of ethyne:

• oxyacetylene welding and cutting

• carbide lamps on bikes lit by dripping ethyne onto calcium dicarbide, and this lamp is still used by cave explorers

Describe the appearance of calcium dicarbide?

grey-brown or sandy, due to the presence of impurities

What impurities can be found in calcium dicarbide?

calcium sulfide CaS

calcium phosphide Ca₃P₂

calcium nitride Ca₃N₂

Key steps + observations in the procedure for the preparation of ethyne:

1. using a spatula, some calcium carbide is placed in a Buchner flask, it must not be touched as moisture from the hand could start the reaction

2. water is added slowly using a dropping funnel

3. fizzing takes place in the Buchner flask, a white solid calcium hydroxide is formed and the Buchner flask becomes warm, as an exothermic reaction is occurring

4. the ethyne gas is bubbled through acidified copper sulfate solution, to remove impurities of hydrogen sulfide, phosphine and ammonia as ethyne does not dissolve

5. bubbles of gas start to come through the delivery tube, a few test tubes of the gas are collected, the first few are discarded as they only contain displaced air

What safety precautions are taken when preparing ethene?

• since ethynes an explosive misture with air, no naked flam should be brought near the gas preparation apparatus, and all tests should be performed away from the apparatus

• after the ethyne is collected the apparatus should be dismantled to ensure no more ethyne is produced

Describe the tests on ethyne?

physical properties

• it is observed that ethyne is a colourless gas with a sweetish smell, but if impurities are still present, it will not smell nice

• insoluble in water; it is only soluble in organic solvents such as cyclohexane and chloroform

combustion

• lid is removed from the gas jar and a lit taper is held at the mouth of the gas jar

  • a more yellow-luminous, smokey flame and great deal of soot is observed

  • the soot is a result of unburnt carbon, due to lack of sufficient oxygen to burn it completely

tests for unsaturation

• bromine water is added to a test tube of ethyne, which is stoppered and shaken

  • colour change from yellow-orange to colourless is observed

  • bromine bonds with the very reactive triple bond to form a new colourless compound

• dilute acidified potassium permanganate is added to a test tube of ethyne, which is stoppered and shaken

  • colour change from purple to colourless is observed

  • the very reactive triple bond reacts with the potassium permanganate to produce an unsaturated product

Write an equation for the complete combustion of ethyne in excess oxygen:

2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O

Describe an experiment which describes the solubillity properties of gases:

• the syringe on the left is filled with 100cm³ of the gas being studied

• the gas is slowly bubbled into water

• the syringe on the right collects any gas which does not dissolve

• methane, ethene and ethyne are all insoluble in water, but soluble in organic solvents

Fractional Distillation

the separation of crude oil into different hydrocarbon compounds based on their boiling points

Describe the process of fractional distillation

• crude oil is heated in a furnace near the bottom of the fractionating column; this keeps the temperature high at the bottom

• hot vapour moves up along the column

• the temperature decreases as you ascend the tower

• as the crude oil rises up the tower, the fractions will reach a temperature that is just below their boiling point and turn into liquids which are collected in trays

• the heavier hydrocarbons will condense first, while the lighter hydrocarbons will rise higher and condense higher up the tower

What are the different fractions + length of carbon chain + their uses?

refinery gas - cooking - C₁ - C₄

light gasoline petrol - C₅ - C₁₀

naphtha - petrol + petrochemical industry - C₇ - C₁₀

kerosene - aircraft fuel

gas oil - diesel cars

lubricating oil - lubricates machines

fuel oil - large ship fuel

bitumen - road tar - greater than C₃₅

What is LPG?

Liquid petroleum Gas - mixture of propane and butane, liquefied under high pressure

What are the residual fractions?

fractions left over when the more volatile fractions boil off; include lubricating oi, fuel oil and bitumen

Does natural gas have a smell?

• no, which is dangerous

• mercaptans are organic sulphur compounds that are added to natural gas so that leaks can be detected

Unsaturated compound

is one that contains one or more double or triple bonds between the carbon atoms in the molecule

Aliphatic compound

an organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties

Aromatic compounds

compounds that contain a benzene ring structure in their molecules

Describe how an internal combustion engine works

• a mixture of petrol and air is drawn into the cylinder

• the mixture is compressed and ignited by a spark

• gases produced by the explosion drive the piston down

• this rotates the crankshaft causing the wheels to turn

Auto ignition

Is premature ignition (explosion) of the petrol-air mixture before normal ignition of the mixture by a spark takes place

Octane number

Of a fuel is a measure of the tendency of the fuel to resist knocking

What are the reference compounds for assigning octane numbers + what are their octane numbers?

heptane - octane number of 0

2,2,4-trimethylpentane (iso-octane) - octane number 100

Catalytic cracking

Is the breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short chain molecules for which there is greater demand

Heat of reaction

Is the heat change when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely

Heat of combustion

Of a substance is the heat change when one mole of the substance is completely burned in excess oxygen

Heat of neutralisation

Is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base

Heat of formation

Of a compound is the heat of change that takes place when one mole of a compound in its standard state is formed from its elements in their standard states

Describe the steps involved in using a bomb calorimeter:

• a known mass of the substance whose heat of combustion is being measured is placed in the crucible inside the bomb

• bomb is filled with oxygen under pressure; oxygen is in excess to ensure the substance will burn completely

• bomb is placed in a known quantity of water contained in the bomb calorimeter

• substance is ignited electrically using an ignition coil of wire

Kilogram calorific value

Of a fuel is the heat energy produced when 1kg of the fuel is completely burned in oxygen

Bond energy

Is the average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other

Hess's law

states that is a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction is carried out in one stage