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  • Topic: Chemical formula, Structural formula, Alkene
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  • Published : March 18, 2012
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1. (a) Alkanes are saturated hydrocarbons.explain the words saturated and hydrocarbons. (b) Alkanes are generally unreactive. Explain why this is so. (c) write balanced equations for the complete combustion of: (i) methane (ii) ethane.

2. Use the passage below and your knowledge to answer the questions that follow.

Methane reacts with bromine to give bromomethane and hydrogen bromide. The mechanism for the reaction is called free-radical substitution and involves hemolytic fission of chemical bonds. The reaction proceeds via initiation, propagation and termination steps.

(a) By what mechanism does bromine react with methane?
(b) Write a balanced symbol equation for this reaction.
(c) Bonds break in this reaction. What type of bond breaking is involved? (d) What essential conditions are required for this reaction? Why? (e) For this reaction, write down an equation for:

(i) An initiation step
(ii) A propagation step
(iii) A termination step.

3. In a similar reaction to the one in the question 2, 1.50g of ethane reacts with chlorine. 1.29g of chloroethane is formed. (AR values: H=1.0, C=12.0, Cl=35.5) Calculate:
(a) The number of moles of ethane that were used
(b) The number of moles of chloroethane that were formed
(c) The percentage yield
(d) The number of grams of chloroethane that would have formed if the percentage yield had been 60.0%.

4. Propene, cis-pent-2-ene and trans-pent-2-ene are alkenes. (a) For each one give:
(i) Its molecular formula
(ii) Its structural formula
(iii) Its displayed formula
(iv) Its skeletal formula.
(b) Give the general formula that is used to represent alkenes. (c) Two of these alkenes are isomers of each other. Identify which two. (d) Why is it not possible to change one of these two isomers into the other at room temperature ? (e) Give the displayed formulae and the names of the four alkenes with...
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