13619.06R [Turn over 13 Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars. It is a liquid at room temperature. Isooctane is one of eighteen structural isomers of C8H18. (a) (i) Draw the skeletal formula of isooctane. [1] (ii) Define the term structural isomers. [2] (iii) Draw the structural formula and state the IUPAC name of the structural isomer of C8H18 which is the most branched. IUPAC name: [2] 13619.06R (b) (i) Write an equation for the complete combustion of isooctane, C8H18. [2] (ii) Suggest why a sooty flame is observed when a sample of isooctane burns. [1] (iii) When 1.00 g of liquid isooctane reacts completely in excess oxygen, the enthalpy change is -47.9 kJ. Calculate the heat energy released when 5.00 dm3 of liquid isooctane burns completely in oxygen (density of isooctane = 0.692 g cm-3). Give your answer to 3 significant figures. Answer                         kJ [3] (c) The combustion of organic compounds has contributed to the increase in the percentage composition of carbon dioxide in the atmosphere. (i) State the percentage increase in atmospheric carbon dioxide caused by the combustion of organic compounds. [1] (ii) State a consequence of an increase in atmospheric carbon dioxide. [1] 13619.06R [Turn over (d) Pollutants such as carbon monoxide and oxides of nitrogen are also produced when alkane fuels are burned. Catalytic converters are used to reduce the environmental impact of burning alkane fuels. They consist of a thin layer of a metal catalyst on a ceramic honeycomb structure. (i) Suggest why a catalytic converter has a honeycomb structure. [1] (ii) Suggest why a thin layer of the metal catalyst is used in a catalytic converter. [1] (iii) Write an equation for the overall reaction between nitrogen(II) oxide and carbon monoxide in a catalytic converter. [2] (iv) Define the term catalyst. [1] (v) State the name given to the graphical distribution of molecular energies in gaseous reactions. [1] 13619.06R (vi) Explain, with reference to the graphical distribution named in (d)(v), how a catalyst changes the rate of reaction between nitrogen(II) oxide and carbon monoxide. [3]