Edexcel Jun 2011 Paper 1 Q19

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19 This question is about alkanes. (a) The skeletal formulae of two alkanes (A and B) are shown below. (i) Write the general formula of the alkanes. (ii) Compounds A and B areof each other. (iii) Draw the displayed formula of compound A. (iv) Give the systematic name of compound B. PMT (1) (1) (1) (1)16 *P38433A01624*<br /> (b) The largest use for alkanes is as fuels. However, there are problems associated with the combustion of alkanes, whether complete or incomplete. (i) An incomplete combustion of methane, CH4, results in the formation of carbon monoxide and water only. Write the equation for this reaction. State symbols are not required. PMT (2) (1) (ii) When does incomplete combustion occur?(iii) State two problems that result from the incomplete combustion of alkane fuels. (2) 12*(iv) State and explain the main environmental problem arising from the complete combustion of alkane fuels. (3)*P38433A01724* 17 Turn over<br /> PMT (c) The reactions of organic compounds, including alkanes, may be broken down into a series of steps; this is the mechanism for the reaction. The reaction between methane and chlorine may be represented by a mechanism involving three stagesinitiation, propagation and termination. (i) Reaction mechanisms often involve the use of curly arrows. Explain the meaning of the curly arrows shown below. (2) Arrow I Arrow II Arrow IArrow II(ii) Using the curly arrow notation, show the initiation step of the reaction between methane and chlorine. (2) 18 *P38433A01824*<br /> (iii) Give the two propagation steps of the reaction between methane and chlorine. Curly arrows are not required. (iv) Suggest why a small amount of UV light can result in the formation of a large amount of product. PMT (2) (1)(v) Ethane is a trace product of this reaction. By means of an equation, show how the ethane is formed. (d) Scientists never detect molecular hydrogen, H2, amongst the products of the chlorination of methane. Use the data below to suggest why this is so. The frequency of UV light used corresponds to an energy of about 400 kJ mol1. Bond C H Cl Cl Bond enthalpy/ kJ mol1 435 243 (1) (2)(Total for Question 19 = 22 marks) *P38433A01924* 19 Turn over<br />

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