Q1.Methane (CH4) is used as a fuel.
(a)     The displayed structure of methane is:

Draw a ring around a part of the displayed structure that represents a covalent bond.
(1)
(b)     Why is methane a compound?
Tick () one box.
 
 	Methane contains atoms of two elements, combined chemically.		
 	Methane is not in the periodic table.		
 	Methane is a mixture of two different elements.		
(1)
(c)     Methane burns in oxygen.
(i)      The diagram below shows the energy level diagram for the complete combustion of methane.
Draw and label arrows on the diagram to show:
•        the activation energy
•        the enthalpy change, ΔH.

(2)

(ii)     Complete and balance the symbol equation for the complete combustion of methane.
                    CH4     +     ..........  CO2       +     ..........
(2)

(iii)    Explain why the incomplete combustion of methane is dangerous.
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(2)

(iv)    Explain why, in terms of the energy involved in bond breaking and bond making, the combustion of methane is exothermic.
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(3)

M1.(a)     circle round any one (or more) of the covalent bonds
any correct indication of the bond − the line between letters
1

(b)     Methane contains atoms of two elements, combined chemically
1

(c)     (i)      activation energy labelled from level of reagents to highest point of curve
ignore arrowheads
1
enthalpy change labelled from reagents to products

arrowhead must go from reagents to products only
1
(ii)     2 O2
1
2 H2O
if not fully correct, award 1 mark for all formulae correct.
ignore state symbols
1
(iii)    carbon monoxide is made
1
this combines with the blood / haemoglobin or prevents oxygen being carried in the blood / round body or kills you or is toxic or poisonous
dependent on first marking point
1
(iv)    energy is taken in / required to break bonds
accept bond breaking is endothermic
1
energy is given out when bonds are made
accept bond making is exothermic
1
the energy given out is greater than the energy taken in
this mark only awarded if both of previous marks awarded
1