AS Level Chemistry: Organic Chemistry


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Question Answer
What are stereoisomers? -Compounds with the same structural formula but with different arrangement of the atoms in space.
What are structural isomers? -Compounds with the same molecular formula but different structural formulae.
When can geometric isomers occur? -When there is a C=C double bond, like in alkenes as the double bonds cannot rotate.
When do Cis/Z isomers occur? -When the similar groups are on the same side of the double bond.
When do Trans/E isomers occur? -When similar groups are opposite one another.
Why are Alkanes also known as saturated hydrocarbons? -As they contain no double C=C bonds, every bond is single.
Why does the boiling point of an alkane depend on its size and shape? -As the longer the carbon chain, the stronger the London forces, as there is more molecular surface for electrons to interact, meaning more energy is needed to break these bonds. -A branched alkane has a lower boiling point than a straight chain as they have smaller molecular surface areas, so London forces are reduced.
Alkanes burn completely in oxygen to produce what? -Carbon dioxide gas, and water/steam(gas)
Halogens can react with alkanes to form haloalkanes what is the name of this mechanism? -Free-radical substitution.
Explain the process of free radical substitution including it's three stages: -UV light begins the first stage, Initiation, where radicals are produced, the UV light breaks the halogen bond i.e Cl-Cl bond, the bond splits equally by homiletic fission, producing 2 free radicals. -In Propagation stage, the free radicals start a chain reaction by reacting with Alkane molecules, producing further radicals. -Termination reactions are where the free radicals are all used up, producing stable molecules.
Why are Alkenes know as UNSATURATED HYDROCARBONS? -As they contain one or more double C=C bonds.
Why are Alkenes more reactive than Alkanes? -As the double bond is made up of a σ bond and a pie bond, and the pie bond is most likely to be attacked by electrophiles. -The double bond also has a really high electron density.
What is an electrophile? -An atom that is is attracted to an electron-rich centre, where it accepts a pair of electrons.
What is a nucleophile? -An atom that is attracted to an electron-deficient carbon atom, where it donates a pair of electrons to form a new covalent bond.
What is a pie bond? -A bond formed by the sideways overlap of two p-orbitals, containing two electrons.
What is a σ (sigma) bond? -A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons.
What is the test for Alkenes? -Bromine water as it tests fro C=C double bonds, as bromine water is a orange brown colour but when added to C=C double bonds it quickly decolourises.
How is ethanol manufactured? -Ethene is hydrated by steam at at 300C with 60atm, with a phosphoric acid catalyst .
What are the properties of LDPE - low density poly(ethene)? -Flexible, strong, deformed by heat.
What are the properties of HDPE-high density Poly(ethene)? -Strong, rigid, not deformed by heat, easy to mould.
What are the safest ways to get rid of plastics? -Some plastics can be recycled however this requires sorting, which is expensive. -Some toxic waste products can be removed when they are burned. -Or burned for energy production.
Why does the boiling point of haloalkanes depend on its size and shape? -As the longer the chain the higher the BP, as there are greater London forces between longer chains. -Haloalkanes with larger halogen atoms have higher BP due to increased London forces, this is also the case when they have more halogen atoms as well.
What is the problem with CFCs? -They break down the ozone layer, as UV light breaks the C-Cl bond creating free radicals which attack ozone molecules.
What oxidising agent can you use to oxidise alcohols? -Potassium dichromate.
What can primary and secondary alcohols be oxidised to? -Primary alcohols can be oxidised to aldehydes, and then refluxed to a carboxylic acid. -Secondary alcohols can be oxidised to ketones only.
What are primary, secondary and tertiary alcohols? -A primary alcohol is when the Carbon bonded to the OH is attached to ONE other alkyl group. --A secondary alcohol is when the carbon boned to the OH is attached to TWO other alkyl groups. -A tertiary alcohol is when the carbon bonded to the OH is attached to THREE other alkyl groups.
In reactions of alcohols, in what type of reaction can a OH be swapped for a halogen to make a haloalkane? -Nucleophilic substitution.
How are aldehydes, ketones and carboxylic acids identified? -Aldehydes have a hydrogen and one alkyl group, as well as a double bond O. -Ketones have two alkyl groups attached to the carbon atom, and a double bond O. -Carboxylic acids have a double bond O and a OH.
By refluxing a secondary alcohol, what would be produced? -A ketone.
what acid is required to turn an alcohol to a haloalkane? -HCl
What is the difference between endothermic and exothermic reactions? -Exothermic reactions give out energy so is -ΔH(negative). E.g Oxidation. -Endothermic reactions take in energy so are +ΔH.
what is the definition of Standard enthalpy change of reaction? -The enthalpy change when the reaction occurs in the molar quantities shown in the equation under standard conditions with everything in its standard state.
What is the definition of standard enthalpy change of formation? -The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
what is the equation of enthalpy change of formation. A=C-B
What is the definition of the standard enthalpy change of combustion? -The enthalpy change when 1 mole of a substance is burned completely in oxygen under standard conditions.
What is the definition of the enthalpy change of neutralisation? -The enthalpy change of neutralisation of a compound is the energy accompanies the reaction of an acid to form one mole of H2O.
What is the equation of the enthalpy change of combustion? A=B-C
What are the factors that affect the rate of a reaction? -Increased concentration or increased pressure, leads to the atoms being closer to each other, so will collide more often, so more successful collision will occur. -Increased surface area, means more atoms can come into contact with other reactants, leading to speedier reactions. -catalysts lower the activation energy, by providing an alternative route, thus meaning more particles have another energy to react.
What are homogenous catalysts? -is a catalyst which is in the same state as the reactants.
What are heterogeneous catalysts? -These catalysts have different physical states from the reactants, and the reactant molecules are often weakly bonded to the surface of the catalyst.
what does Le Chatelier's principle tell you? -The position of equilibrium.
How does Le Chatelier's principle work? -If the conc of a reactant in increased the equilibrium will shift to the right. Whereas if the conc of the product is increased it will shift to the left. If pressure increases the shift will go to the side with the least gas molecules. -
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