11 - Organic Chemistry Flashcards
Why do fuels release energy?
Because combustion is exothermic. Activation energy is needed to break the bonds, which requires energy and is an endothermic process. The enthalpy of these bonds broken is not as high as the enthalpy of the bonds formed, which is exothermic. This means we have a negative enthalpy change (overall energy release to the surroundings).
Which fuel is the most effective between wood, ethanol or wax
- Which one releases more energy?
- Which one lasts longer?
Ethanol releases most energy (more power)
Wax lasts longer (more Joules per gram)
What is the general formula for the Alkene family
CnH2n
What is the general formula for the Alcohol family
Cn H2n+1OH
What is the general formula for the Alkane family
CnH2n+2
State 3 members of the Alkane family
CH4 - Methane (single carbon bond)
C2H6 - Ethane (idem)
C3H8 - Propane
State 2 members of the alcohol family
CH3OH - Methanol
C2H5OH - Ethanol
(they ends in OH)
How do molecules of Alkane look like ?
Chains of carbon surrounded by hydrogens
How do molecules of Alkene look like ?
A chain of carbons with one double Bond surrounded by hydrogens
How do molecules of Alcohol look like ?
A chain of carbons connected with an oxygen and a hydrogen at the end the rest is surrounded by hydrogens
What is in crude oil?
Mostly liquid alkanes
Hexane and above are liquid
Which molecules make up natural gases
80% is CH4 - Methane (1 carbon)
20% is - C2H6 - Ethane (2carbon)
- C3H8 - propane (3 carbon)
- C4H10 - Butane (4 carbon)
What is the general formula for alkane gas molecules
Cn H2n+2
Def. fuel
A substance that when burnt completely in oxygen releases heat energy (and forms waste products in the form of oxides)
What waste products do you get from combusting Carbon?
CO2
What waste products do you get from combusting Hydrogen?
H2O
What waste products do you get from combusting Propane?
CO2 + H2O
What is smoke and when is it formed?
Smoke is particles of carbon and is formed instead of Carbon dioxide by an insufficiency of oxygen to react with during combustion. Carbon monoxide can also be formed.
What is smoke and when is it formed?
Smoke is particles of carbon and is formed instead of Carbon dioxide by an insufficiency of oxygen to react with during combustion. Carbon monoxide can also be formed.
What is in crude oil/petroleum?
Alkanes
What is a fossil fuel?
A fuel made from dead organisms that have fossilised over time
What temperature is crude oil heated to in fractional distillation?
350 Degrees Celcius
How does fractional distillation separate crude oil?
The larger the molecules (alkane chains) are, the stronger intermolecular forces they have. This means they have a higher boiling point.
The smaller the molecules are, the weaker intermolecular forces they have. This means they have a lower boiling point.
The molecules with a lower boiling point move higher through the fractionating column before condensing, while substances with a highest boiling point will condense quickly.
What fractions are formed during the distillation of crude oil, and what are their purposes?
From smallest to largest
- Bottled/Refinery gas - miscelaneous
- Gasoline - Cars
- Naphta - Experiments
- Kerosene - Planes
- Diesel oil - Cars, lorries, buses
- Fuel oil - Ships, power stations
- Bitumen - Roads and roofs
How does fractional distillation of air work?
Air is cooled to -200 degrees celcius.
Carbon dioxide freezes and is removed. The other gases condense.
The liquid is distillated through the fractionating column, seperating Nitrogen, Argon, Oxygen and Krypton.
Def. Organic Compounds
Compounds made from carbon and hydrgen, and possibly other non-metals
Def. Homologous series
A family of similar compounds with similar chemical properties due to the presence of the same functional group
Def. Functional group
An atom or group of atoms that determine the chemical propertiesof a homologous series
What are the characteristcs of homologous series?
- They have the same functional group
- They have the same general formula
- They differ from one member to the next by one CH2 unit
- They display a trend in chemical properties
- They have similar chemical properties
What s the functional group of alkanes?
CC single bond
What is the functional group of alkenes?
CC double bond
Def. Isomer
Compounds that have the same molecular formula but different structural formula and arrangement of atoms
Def. Saturated hydrocarbon
Hydrocarbons in which all CC bonds are single bonds
What is the functional group of alcohols?
OH
What is the functional group of carboxylic acids?
COOH
What is the general formula for carboxylic acids?
CnH2n+1COOH
What are the properties of alkanes?
- Generally unreactive
- Exept in terms of combusion
- And substitution with chlorine
Def. Substitution reaction
One atom or group of atoms is replaced by another atom or group of atoms
What type of reaction is the substitution of Alkanes by Chlorine?
Linked to conditions needed for the reaction to occur
Photochemical reaction
This means that ultraviolet provides activation energy for the reaction
What is the formula for the complete combustion of alkanes?
For the example, use methane
CH4 + O2 → CO2 + H2O
What gases are produced during incomplete combustion of Alkanes?
CO2
and at least on of
CO and C
What is the main disadvantage of CO2?
Global warming as it absorbs reflected heat in the atmosphere
What is the main disadvantage of CO?
It is poisonous
WHat is the main disadvantage of carbon (g), or smoke?
It can cause respiratory problems
What is the formula for the substitution of Methane by Chlorine?
CH4 + Cl2 → CH3Cl + HCl
Describe the cracking of alkanes
Cracking of Alkenes is the thermal decomposition reaction in which larger alkanes are broken down into smaller, more useful hydrocarbon molecules, some of which are alkenes. The products of cracking include alkanes, hydrogen gas and alkenes.
What are the purposes of the cracking reaction?
- It produces alkenes
- It produces shorter-chain alkanes e.g. gasoline
What is the test for saturated hydrocarbons?
Adding bromine water and seeing if it turns from orange to colourless
If they do, they are unsaturated
What are the conditions needed for the cracking of Alkanes?
Heat and a Catalyst
How many products are formed in an addition reaction?
One
How are the products retrieved from the cracking of alkanes?
Fractional Distillation
What type of reaction is the cracking of alkanes?
Thermal decomposition
What is an addition reaction?
When two or more products combine into one product
What are the three types of addition reactions that we need to know?
- Halogenation (adding a halogen molecule across a C=C double bond)
- Hydrogenation (adding a hydrogen molecule across a C=C double bond) - this only occurs in the presence of a nickel catalyst
- Hydration (adding a water molecule across a C=C double bond) - this only occurs in the presence of an acid catalyst
Which hydrocarbons are used to test for saturated hydrocarbonswith bromine water, and what are the outcomes?
- Cyclohexane - orange mixture
- Cyclohexene - colourless mixture
Describe the manufacture of alcohol by fermentation
- Fermentation in aqueous glucose at 25 - 35 degrees Celsius in the presence of yeast and the absence of oxygen
Describe the manufacture of alcohol from ethene
Catalytic addition of ethene at 300 degrees Celsius and 6000kPa/60atm in the presence of an acid catalyst
What are the advantages of fermentation?
- Fermentation can happen just above room temperature so is relatively inexpensive
- The glucose for fermentation is produced by plants, therefore fermentation is sustainable
What are the disadvantages of fermentation?
- If air is present during fermentation, ethanoic acid is produced
- Yeast can be denatured if the temperature is too high
- Fermentation is a slow process
- The maximum concentration of ethanol produced during fermentation is 12-15%
- Fermentation only produces one type of alcohol: ethanol
- Ethanol must be extracted from the fermentation mixture by fractional distillation
- The use of crops could impact the food supply
- requires ethanol to be produced in batches so it is a stop-start process
What are the advantages of the catalytic addition of steam to ethene?
- Different alcohols can be produced by using different Alkenes
- The hydration of ethene is fast and can produce ethanol continuously to meet market demands.
- The hydration of ethene only produces one product so does not need refinement
- The hydration of ethene can be automated, requiring little input from workers
What are the disadvantages of the catalytic addition of steam to ethene?
- High temperatures and pressures are required for the hydration of ethene
- The hydration of ethene requires ethene from crude oil which is unsustainable
Why is incomplete combustion less likely to occur for alcohols than other alkanes or alkenes?
Alcohols already contain oxygen so the lack of hydrogen during the reaction is less likely
Describe the oxidation of ethanol to ethanoic acid by oxygen molecules
Oxygen from the air reacts with ethanol molecules to produce water and ethanoic acid
e.g. Red wine to vinegar
Describe the oxidation of ethanol to ethanoic acid without oxygen molecules
Acidified potassium manganate (VII) reacts with alcohol with heat and turns from purple to colourless.
What are the uses of ethanol?
- As a solvent e.g. paints, inks perfumes and cleaning products
- As a fuel e.g. for cooking or biofuels for vehicles
Describe the reaction between an alcohol and a carboxylic acid
This reaction requires and acid catalyst and forms an ester and water
What are esters?
Sweet, fruity-smelling fluids found naturally in fruits and produced artificially for flavourings
What is condensation polymerisation?
A reaction formed from alcohols, carboxylic acids and amines that produces two products in the form of a polymer and small molecules
What is a polymer chain?
They are long chains of two different alternating monomers
The backbone of a polymer contains carbon, oxygen, and sometimes nitrogen
What are the typical uses of plastics and synthetic fibres?
e.g. nylon or PET
Polyesters e.g. PET - Used for fabric/clothing/water bottles
Polyamides e.g. Nylon - Used for fabric/clothing/ropes/fishing lines
What are polyesters made from?
2 types of monomers:
- Diols
- Di-carboxylic acids
What are polyamines made from?
2 types of monomers:
- Di-amines
- Di-carboxylic acids
How are polyamines and poly esters formed?
By condensation polymerisation using reactants with 2 reactive ends
What are the differences between addition and condensation polymers?
Addition Polymers:
- Formed from alkenes
- Only one product, the polymer, is formed
- The name of the polymer is polyalkene
- The backbone of the polymer is a carbon chain
Codensation Polymers:
- Formed from (di-)ethanols, (di-)carboxylic acids and (di-)amines
- Two types of products are formed - the polymer and smaller molecules
- The backbone of this polymer contains C, O, and sometimes N
How is PET recycled?
Can be converted back into monomers then re-polymerised
What are proteins?
Natural polymers composed of amino acids
What functional groups does an amino acid have?
- Amine group
- Carboxylic acid group
- ‘R’, another group that can change
What is the functional group of protein?
Amide
What is the amide functional group?
CONH
C=O-N-H
What is the amino functional group?
NH2
What is the ester functional group?
COO
What are the environmental challenges caused by plastics?
- Disposal in landfill sites
- Accumulation in the oceans
- Formation of toxic gases from combustion
Give an example of addition polymerisation
The formation of poly(ethene) from ethene monomers with heat and a catalyst
What are the main properties of plastics?
- Nonbiodegradable
- Unreactive
