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Edexcel AS Chemistry module 2 revision thread.

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    Who's doing this module in the summer?
    How is everyone's revision going?
    Post revision questions here.
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    i have a question
    what is the difference between thermodynamic stability and kinetic stability?
    also if you have some mark schemes for past edexcel papers then plz pm me
    thanks
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    From what I understand thermodynamic stability is to do with the feasbility of a reaction, which way you'd expect a reaction to go. For example in an exothermic reaction, the products are said to be thermodynamically stable relative to the reactants, because they are at a lower enthalpy level. With an endothermic reaction it's the other way round, because the reactants are at a lower enthalpy level relative to the products (so the reactants are thermodynamically stable).

    Some reactions you'd expect to occur spontaneously, that is some exothermic reactions (i.e. from thermodynamically unstable reactants to stable products) but they DONT and that's because the reactants are often kinetically stable, that is the activation energy required for the reaction to go is too high. The classic example in almost every textbook is the reaction of carbon(diamond) turning to carbon (graphite), where carbon(graphite) is thermodynamically stable, but the reaction has such a high activation energy that the reaction doesn't go, the conditions simply aren't right.
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    ^ That is the best answer. If you wrote that in the exam you would full marks.
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    Sod everything else, that's really easy, organic chemistry is needed.
    I'll copy and paste the spec bit here so we (jun 05 c2 students and anyone else) can discuss it. I got an A in my C2 and C3B mocks which I can't quite believe because my organic chemistry is weaker than other bits of the spec.

    TOPIC 2.2: ORGANIC CHEMISTRY 1 (INTRODUCTION, ALKANES, ALKENES, HALOGENOALKANES AND ALCOHOLS)

    The following is intended to introduce the study of organic chemistry.
    Related topics at A2 will assume knowledge of this material.

    a - Introduction
    Students should be able to:
    i - understand the concept of homologous series
    ii - apply the rules for IUPAC nomenclature for compounds relevant to this specification
    iii - recognise and predict the existence of structural isomerism within the types of compounds found in this topic
    iv - recognise the existence of geometric (cis-trans) isomerism resulting from restricted rotation about a carbon-carbon double bond
    v - be able to classify reactions as free radical, electrophilic addition, nucleophilic substitution, elimination, hydrolysis, reduction, oxidation or polymerisation.
    • details of mechanism are not required at AS.
    • understanding of the terms electrophile, nucleophile and free radical is expected.

    b - Reactions of organic compounds
    Students should be able to recall, in terms of reagents and general reaction conditions, the reactions of:
    i - alkanes with oxygen (air), chlorine and bromine
    ii - alkenes (to include unsymmetrical alkenes) with hydrogen, halogens, hydrogen halides and potassium manganate(VII).
    The use of bromine solution as a test for alkenes (paper 3B only)
    iii - halogeno-compounds with potassium hydroxide (to produce alcohols or alkenes) potassium cyanide and ammonia.
    Identification of the halide group by alkaline hydrolysis, subsequent acidification and testing with aqueous silver nitrate (paper 3B only)
    iv - primary, secondary and tertiary alcohols with acidified potassium dichromate(VI), dehydrating agents (eg concentrated sulphuric acid) and halogenating agents (phosphorus pentachloride, sodium bromide and concentrated sulphuric acid, phosphorus and iodine).
    The use of phosphorus pentachloride as a test for the –OH group (paper 3B only)
    • knowledge of the elimination of water between two molecules of alcohol to produce ethers will not be expected

    c - Bonding and reactivity
    Students should be able to use the concepts of single and double covalent bonds, bond polarity and bond enthalpy as factors influencing relative reactivity in appropriate reactions of alkanes, alkenes, halogenoalkanes and alcohols.

    d - Quantitative chemistry related to this topic
    Students should be able to calculate:
    i - empirical and molecular formulae
    ii - theoretical yield and percentage yield in reactions, from reacting mass data (paper 3B only)
    • to include calculations in which one reagent is in excess.

    e - Applied organic chemistry
    Students should be able to discuss:
    i - the advantages and disadvantages of liquid and gaseous fuels
    • limited to hydrogen, ethanol, methane, butane and octane
    • including calculations of energy evolved per unit mass and per unit volume
    • including environmental factors
    ii - the structures and properties of the polymers of simple alkenes and their uses;
    • limited to poly(ethene), poly(propene), poly(chloroethene), poly(tetrafluoroethene)
    • including representative structural formulae, making clear the repeating unit
    iii - recall that halogens are used in the manufacture of herbicides and polymers; understand that the strength of the C–X bond gives a useful life to many of these compounds, but may lead to problems of disposal and persistence in the food chain.
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    Okay, Organic Chemistry.

    Here are some revision questions!

    1) A sample of compound P was found to give steamy acidic fumes of HCL when solid PCl5 was added to a small sample in a clean, dry test tube.

    a) What functional group does compound P contain? (1)

    b) Explain why a dry test tube had to be used? (2)

    Compound P has two isomers. Upon heating one of the isomers potassium dichromate (VI) acidified with dilute sulphuric acid, propanoic acid was produced. The second isomer does not produce propanoic acid.

    c) Draw the structural formula for the second isomer of P. (2)
    (You can do this bit on Paint!)

    d) Draw the structural formula for the product that would be obtained when the second isomer of P was heated with potassium dichromate (VI) with dilute sulphuric acid. (2)

    e) What is meant by dehydration? (2)

    f) State 2 conditions required for the dehydration of an alcohol? (2)

    g) Name the product that would be formed if 2-methylbutan-2-ol was dehydrated (1).
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    Here are some revision questions!

    1) A sample of compound P was found to give steamy acidic fumes of HCL when solid PCl5 was added to a small sample in a clean, dry test tube.

    a) What functional group does compound P contain? (1)
    OH-

    b) Explain why a dry test tube had to be used? (2)
    So that no other liquid/aqeous reagents interfere with the test.

    Compound P has two isomers. Upon heating one of the isomers potassium dichromate (VI) acidified with dilute sulphuric acid, propanoic acid was produced. The second isomer does not produce propanoic acid.

    c) Draw the structural formula for the second isomer of P. (2)
    CH3CH(OH)CH3
    Primary alcohols react to give aldehydes then carboxylic acids. Secondary alcohols react to give ketones, so isomer must be a secondary alcohol.


    d) Draw the structural formula for the product that would be obtained when the second isomer of P was heated with potassium dichromate (VI) with dilute sulphuric acid. (2)
    CH3COCH3

    e) What is meant by dehydration? (2)
    A chemical reaction in which two molecules react with each other with the loss of water from one of the molecules (ie loss of water from an alcohol to form an alkene)

    f) State 2 conditions required for the dehydration of an alcohol? (2)
    Concentrated sulphuric acid as the dehydrating agent, heat (under reflux) to catalyse the reaction.

    g) Name the product that would be formed if 2-methylbutan-2-ol was dehydrated (1).
    C5H10 (pentene)
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    i had a basic question
    state one large-scale use of sodium chlorate(I)
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    to manufacture herbicides (weed killers)
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    One more use NaClo can make explosives
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    also i hv this unit 1 question (sorry for putting it in the wrong thread)
    it was something like why does a compoung give out a flame colour like why is the flame colour of potassium ion lilac (i cant remember the exact words)
    thanks
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    "why does a compoung give out a flame colour like why is the flame colour of potassium ion lilac"

    This is becuase when you put Potassium in a flame you give the electrons energy. They jump to higher energy levels and when they fall down they release light which gives an indication of the energy gap between orbitals. This means that specific frequencies will be released, eg. lilac with potassium, by specific orbital energy gaps which differ between the metals.

    Thermodynamic stability indicates that the products of the reaction are at a lower energy level than the reactants, and the reaction is exothermic. Kinetic stability indicates a high relative activation energy.
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    (Original post by theunforgiven)
    also i hv this unit 1 question (sorry for putting it in the wrong thread)
    it was something like why does a compoung give out a flame colour like why is the flame colour of potassium ion lilac (i cant remember the exact words)
    thanks
    Heat from the flame excites an electron to a higher energy level. The electron then returns to a lower energy level. This excess energy is released as light energy. The frequency of the flame colour depends upon the difference between the energy levles involved.
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    Which chemistry book/revision guide are people using?? We were given a "chemistry in context" book, which has a lot of detail (!) and a "making the grade" revision book, which is erm crap...our teacher told us that if we learn everything in that book, we'll only get a C?! I bought the letts guide, which is ok...and im using the green NAS books, as well.
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    some unit 2 defenitions:

    define:

    enthalpy of formation
    enthalpy of combustion
    homologous series

    state the procedure for the refining of bauxite, 6 marks.

    why is there a semi permeable barrier in the electrolysis tank between the anode and cathode in the electrolysis of NaCl, and give half equations for the reactions at the anode and cathode.

    give an equation of the reaction and name a use for the product if this barrier were to be removed.

    state the reagents and conditions for the oxidation of propanol to a carboxilic acid.

    state the reagent and conditions, and draw the products of the hydrolysis of transbutene

    give the name of the reaction and product between the reactants:
    - propanamine and KCN
    - 1,2-dichloroethane and KOH in ethanol

    some more sutff ...!
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    (Original post by *girlie*)
    Which chemistry book/revision guide are people using?? We were given a "chemistry in context" book, which has a lot of detail (!) and a "making the grade" revision book, which is erm crap...our teacher told us that if we learn everything in that book, we'll only get a C?! I bought the letts guide, which is ok...and im using the green NAS books, as well.
    Make the grade is perfect for edexcel IMO
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    Predict the MAJOR organic products for each of the following reactions.

    (a) CH3CH2CH2CH3 reacting with Cl2 in the presence of UV light

    (b) CH3CH(CH3)CH3 reacting with Cl2 in the presence of UV light

    (c) CH3COOH reacting with Br2 in the presence of UV light

    (d) C6H14 burning in excess oxygen

    (e) CH3CH2CH3 burning in a shortage of oxygen

    (f) CH3CH2OH reacting with Cl2 in UV light
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    One of the isomers of C4H8 reacts with HBR to give 2 different products, the major one of which is a chiral molecule.

    i) Identify this isomer of C4H8
    ii) Give the mechanism for the reaction of this isomer with HBr
    iii)why is the major product Chiral, but the minor one not?
    iv) Why is the chiral product the major one, and the non-chiral the minor one?
    v) The major product of this addition reaction is found to be optically inactive, explain why?
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    define:

    enthalpy of formation
    enthalpy change when 1 mole of substance is formed from its elements in their most stable state at 1 atm pressure and 298K (or a specified temperature)

    enthalpy of combustion
    enthalpy change when 1 mole of substance is burned completely in excess oxygen (to form CO2 and H2O) under standard conditions, at 1 atm pressure and 298K (or a specified temperature)

    homologous series
    A series of compounds that have the same general formula (ie CnHn), have similar chemical properties and differ by CH2.

    I'll do the rest, later. Thanks for the questions everyone!
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    (Original post by ARCHK0VEN)
    Predict the MAJOR organic products for each of the following reactions.
    (a) CH3CH2CH2CH3 reacting with Cl2 in the presence of UV light
    CH3CH2CH2CH3 + Cl2 --> HCl + CH3CH(Cl)CH2CH3
    Free radical addition, so products are is 2-dichlorobutane and hydrochloric acid.

    (b) CH3CH(CH3)CH3 reacting with Cl2 in the presence of UV light
    CH3CH2CH2CH3 + Cl2 --> HCl + CH3CH2CH(Cl)CH3
    Free radical addition, so products are 2-chlorobutane and hydrochloric acid

    (c) CH3COOH reacting with Br2 in the presence of UV light
    Not sure.

    (d) C6H14 burning in excess oxygen
    2C6H14 + 19O2 --> 14H2O + 12CO2

    (e) CH3CH2CH3 burning in a shortage of oxygen
    2C3H8 + 7O2 --> 6CO + 8H2O

    (f) CH3CH2OH reacting with Cl2 in UV light
    Not sure
Updated: June 3, 2005
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