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(a) (i) State the effect of a catalyst on a reaction. Explain how a catalyst causes this effect. ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ [2]
(ii) State the meaning of the term heterogeneous as applied to catalysts. ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ [1]
(b) Some bond energies are given.
[Table_1]
Use the data, and the enthalpy change for the conversion of sulfur dioxide into sulfur trioxide, to calculate a value for the S=O bond energy in SO₃.
S=O bond energy in SO₃ = ............................. kJ mol⁻¹ [2]
(c) A reaction pathway diagram for both the catalysed and uncatalysed reactions between SO₂ and O₂ is shown.
The letters A–E represent energy changes.
Complete the table by stating which letter, A–E, represents the energy change described.
[Table_2] [3]
(d) (i) State and explain the effect of increasing temperature on the rate of production of SO₃. ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ [3]
(ii) State and explain the effect of increasing temperature on the yield of SO₃. ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ [3]
(e) The SO₃ produced is converted to sulfuric acid in two stages. In the first stage the SO₃ is reacted with concentrated sulfuric acid to produce oleum, H₂S₂O₇. The oleum is then reacted with water to form sulfuric acid.
Suggest an equation for the reaction of oleum, H₂S₂O₇, with water to form sulfuric acid. ........................................................................................................................................ [1]
(f) SO₂ reacts with water to form sulfurous acid.
Sulfurous acid is a weak Brønsted-Lowry acid, while sulfuric acid is a strong Brønsted-Lowry acid.
(i) Complete the 'dot-and-cross' diagram to show the bonding in a molecule of SO₂. Show outer electrons only. [1]
(ii) State the meaning of the term strong Brønsted-Lowry acid. ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ [2]
(iii) Write an equation to show the acid-base behaviour of sulfuric acid with water. Include state symbols. ........................................................................................................................................ ........................................................................................................................................ [2]
563
595
517
Crude oil is a complex mixture of hydrocarbon molecules.
The hydrocarbon molecules in crude oil are separated by fractional distillation. Fractional distillation is used because the different hydrocarbon molecules in crude oil have different boiling points.
(a) Explain why the hydrocarbon molecules in crude oil have different boiling points.
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(b) Some of the hydrocarbon molecules obtained from crude oil are processed further by cracking.
Suggest why some hydrocarbon molecules are processed further by cracking.
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(c) Cracking one mole of dodecane, $C_{12}H_{26}$, produces two moles of ethene and one mole of another hydrocarbon molecule.
(i) Write the equation for this cracking reaction.
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The ethene can be used in the production of poly(ethene).
(ii) Give the full name of the process used to produce poly(ethene) from ethene.
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(iii) Give two reasons why poly(ethene) should be reused or recycled rather than just thrown away.
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(iv) Part of a polymer chain, produced by the same type of process as poly(ethene), is shown.
Give the displayed formula of the monomer used to produce this polymer.
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574
567
584
The elements in the third period exhibit periodicity in both their chemical and physical properties.
(a) A graph of the atomic and ionic radii across the third period is shown.
(i) Explain the decrease in atomic radius across the third period.
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(ii) Explain why, for sodium to silicon, the ionic radii are less than the atomic radii.
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(iii) Explain why, for phosphorus to chlorine, the ionic radii are greater than the atomic radii.
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(b) The first ionisation energies of the elements across the third period show a general increase.
Aluminium and sulfur do not follow this general trend.
(i) Explain why aluminium has a lower first ionisation energy than magnesium.
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(ii) Explain why sulfur has a lower first ionisation energy than phosphorus.
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(c) The elements in the third period, from sodium to silicon, can react with chlorine to form chlorides.
(i) State and explain the pattern of change of oxidation number which occurs to both chlorine and the different Period 3 elements when they react together.
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(ii) Give the equations to show the reactions of sodium chloride and silicon(IV) chloride when separately added to water.
sodium chloride ...................................................................................................................................................................................
silicon(IV) chloride ................................................................................................................................................................................... [2]
(iii) Complete the table to describe the structure and bonding in sodium chloride and silicon(IV) chloride.
[Table_1] [2]
566
584
512
X is CH₃CH(OH)CH₂CH₃.
(a) The reaction between X and alkaline aqueous iodine produces a yellow precipitate.
(i) Give the name of the compound formed as a yellow precipitate in this reaction.
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(ii) Give the name of X.
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(b) There are three structural isomers of X that are alcohols.
Draw the structures of these three isomers of X.
[2]
(c) Two reactions of X are shown.
CH₃CH(OH)CH₂CH₃ → CH₃COCH₂CH₃reaction 1 reaction 2
X
↓
C₄H₈
(i) Identify the type of reaction involved in reaction 1.
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(ii) Identify the reagents for reaction 1.
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(iii) Reaction 2 can be carried out by passing the vapour of X over hot aluminium oxide.
The product of reaction 2, C₄H₈, is actually a mixture of three isomers.
Give the full names of the three isomers formed by reaction 2.
1 ...........................................................................................................................
2 ...........................................................................................................................
3 ........................................................................................................................... [3]
(d) The reaction of methylpropene, $(CH_3)_2CCH_2$, with hydrogen bromide, HBr, produces a mixture of two halogenoalkanes.
One of the halogenoalkanes, 2-bromo-2-methylpropane, is formed as the major product while 1-bromo-2-methylpropane is formed in small quantities.
(i) Complete the mechanism to show the reaction of methylpropene with HBr to form the major product.
Include the structure of the intermediate and all necessary charges, dipoles, lone pairs and curly arrows. The structure of 2-bromo-2-methylpropane is not required.
CH₃ H[4]
│ │
H₃C─C─C─H ⟶ 2-bromo-2-methylpropane
││
H Br
(ii) Explain why 2-bromo-2-methylpropane is the major product of this reaction.
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511
598
575
