11.2. The chemical properties of the halogen elements and the hydrogen halides
A subsection of Chemistry, 9701, through 11. Group 17
Listing 10 of 102 questions
Use By choosing the chlorides of two of the Group IV elements as examples, describe the trend in the reactions of these chlorides with water. Suggest an explanation for any differences, and write equations for any reactions that occur. The standard enthalpy changes of formation of lead(chloride and lead(chloride are given in the following table. compound ∆H o f / kJ mol–1 PbCl2–359 PbCl4–329 Use these data, and also bond energy data from the Data Booklet, to calculate the enthalpy changes for the following two reactions. CCl2+ Cl2CCl4∆H o = kJ mol–1 PbCl2+ Cl2PbCl4∆H o = kJ mol–1 Make use of your answers to parts and to suggest how the relative stabilities of the two oxidation states vary down the Group.
9701_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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What is meant by the term bond energy? Describe and explain what is observed when a red-hot wire is plunged into separate samples of the gaseous hydrogen halides HCl and HI. How are bond energy values useful in interpreting these observations? The following reaction occurs in the gas phase. 3F2+ Cl22ClF3, ∆H o— r = –328 kJ mol–1 Use these and other data from the Data Booklet to calculate the average bond energy of the Cl-F bond in Cl F3.
9701_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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A possible source of energy for the road vehicles of the future is hydrogen. One of the problems still to be solved is the storage of the hydrogen in the vehicle. A conventional tank holding liquid hydrogen would have to be pressurised and refrigerated. In a crash, this type of tank could break resulting in the rapid release of hydrogen and an explosion. One alternative is to use a fuel tank packed with carbon nanotubes. The hydrogen in the tank would be adsorbed onto the surface of the nanotubes at a pressure of no more than a few atmospheres. What is the approximate width of a carbon nanotube? In what structural form is the carbon in a nanotube? What forces could be responsible for holding the hydrogen on the surface of the nanotubes? Explain your answer. The hydrogen atoms in a fuel tank packed with nanotubes are closer together than in liquid hydrogen. Suggest one advantage of this. When a nanotube-packed fuel tank is full of hydrogen there is a steady pressure of hydrogen in the tank. While hydrogen gas is being removed from the fuel tank to power the car, the pressure in the fuel tank drops very little for some time. State Le Chatelier’s principle, and suggest how it explains this observation.
9701_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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A possible source of energy for the road vehicles of the future is hydrogen. One of the problems still to be solved is the storage of the hydrogen in the vehicle. A conventional tank holding liquid hydrogen would have to be pressurised and refrigerated. In a crash, this type of tank could break resulting in the rapid release of hydrogen and an explosion. One alternative is to use a fuel tank packed with carbon nanotubes. The hydrogen in the tank would be adsorbed onto the surface of the nanotubes at a pressure of no more than a few atmospheres. What is the approximate width of a carbon nanotube? In what structural form is the carbon in a nanotube? What forces could be responsible for holding the hydrogen on the surface of the nanotubes? Explain your answer. The hydrogen atoms in a fuel tank packed with nanotubes are closer together than in liquid hydrogen. Suggest one advantage of this. When a nanotube-packed fuel tank is full of hydrogen there is a steady pressure of hydrogen in the tank. While hydrogen gas is being removed from the fuel tank to power the car, the pressure in the fuel tank drops very little for some time. State Le Chatelier’s principle, and suggest how it explains this observation.
9701_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Each of the Group VII elements chlorine, bromine and iodine forms a hydride. Outline how the relative thermal stabilities of these hydrides change from HCl to HI. Explain the variation you have outlined in . Hydrogen iodide can be made by heating together hydrogen gas and iodine vapour. The reaction is incomplete. H2+ I22HIWrite an expression for Kc and state the units. Kc = units For this equilibrium, the numerical value of the equilibrium constant Kc is 140 at 500 K and 59 at 650 K. Use this information to state and explain the effect of the following changes on the equilibrium position. increasing the pressure applied to the equilibrium decreasing the temperature of the equilibrium A mixture of 0.02 mol of hydrogen and 0.02 mol of iodine was placed in a 1 dm3 fl ask and allowed to come to equilibrium at 650 K. Calculate the amount, in moles, of each substance present in the equilibrium mixture at 650 K. H2+ I22HIinitial moles 0.02 0.02
9701_w12_qp_21
THEORY
2012
Paper 2, Variant 1
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Each of the Group VII elements chlorine, bromine and iodine forms a hydride. Outline how the relative thermal stabilities of these hydrides change from HCl to HI. Explain the variation you have outlined in . Hydrogen iodide can be made by heating together hydrogen gas and iodine vapour. The reaction is incomplete. H2+ I22HIWrite an expression for Kc and state the units. Kc = units For this equilibrium, the numerical value of the equilibrium constant Kc is 140 at 500 K and 59 at 650 K. Use this information to state and explain the effect of the following changes on the equilibrium position. increasing the pressure applied to the equilibrium decreasing the temperature of the equilibrium A mixture of 0.02 mol of hydrogen and 0.02 mol of iodine was placed in a 1 dm3 fl ask and allowed to come to equilibrium at 650 K. Calculate the amount, in moles, of each substance present in the equilibrium mixture at 650 K. H2+ I22HIinitial moles 0.02 0.02
9701_w12_qp_22
THEORY
2012
Paper 2, Variant 2
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Ammonia, NH3, and methane, CH4, are the hydrides of elements which are next to one another in the Periodic Table. In the boxes below, draw the ‘dot-and-cross’ diagram of a molecule of each of these compounds. Show outer electrons only. State the shape of each molecule. NH3 CH4 shape shape Ammonia is polar whereas methane is non-polar. The physical properties of the two compounds are different. Explain, using ammonia as the example, the meaning of the term bond polarity. Explain why the ammonia molecule is polar. State one physical property of ammonia which is caused by its polarity. When ammonia gas is mixed with hydrogen chloride, white, solid ammonium chloride is formed. State each type of bond that is present in one formula unit of ammonium chloride and how many of each type are present. You may draw diagrams.
9701_w13_qp_23
THEORY
2013
Paper 2, Variant 3
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Write equations, with state symbols, to defi ne the following. the C–Br bond energy in CH3Br the Al –Cl bond energy in Al Cl 3 Describe and explain the trend in bond energies of the bonds in Cl 2, Br2 and I2. Fluorine, F2, does not follow this trend. Suggest a possible reason why. Use data from the Data Booklet to calculate the enthalpy change of the following reaction. H2+ X2→ 2HXwhen X = Cl ∆H = kJ mol–1 when X = I ∆H = kJ mol–1 Use these results to describe and explain the trend in the thermal stabilities of the hydrides of Group VII. Bromine reacts with hot NaOHto give a solution which on cooling produces white crystals of compound A. A has the following percentage composition by mass: Na, 15.2; O, 31.8; Br, 53.0. The remaining solution contains mostly NaBr, with a little of compound A. Calculate the empirical formula of A. Construct an equation for the reaction between Br2 and hot NaOH.
9701_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Questions Discovered
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