# KOH(aq) + HNO 3 (aq) KNO 3 (aq) + H 2 O(l) A 52 B 26 C +26 D +52. (Total for Question = 1 mark) 2 Calculate the enthalpy change, in kj mol _ 1

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1 1 When 0.1 mol of aqueous potassium hydroxide was added to 0.1 mol of nitric acid, 5200 J were transferred to the surroundings. What is the enthalpy change, in kj mol 1, for this reaction? C KOH(aq) + HNO 3 (aq) KNO 3 (aq) + H 2 O(l) 2 Calculate the enthalpy change, in kj mol _ 1, for the reaction H2(g) + ½O 2 (g) H 2 O(g) T: ond ond enthalpy / kj mol _ 1 H H +436 O=O +498 H O C

2 3 The table shows some data about metal ions, non-metal ions and their compounds. Ion Use the data to calculate Mg 2+ (g) 1921 Cl (g) 340 Cs + (g) 276 F (g) 483 Enthalpy change of hydration / kj mol 1 Compound Lattice energy / kj mol 1 MgCl 2 (s) 2526 CsF(s) 747 (a) the standard enthalpy change, in kj mol 1, for the following process C Mg 2+ (g) + 2Cl (g) Mg 2+ (aq) + 2Cl (aq) (1) (b) the standard enthalpy change of solution, in kj mol 1, of caesium fluoride, CsF. 12 (1) +12 C = 2 marks)

3 4 The standard enthalpy change for the combustion of graphite is kj mol 1 and that of diamond is kj mol 1. What is the standard enthalpy change for the reaction below, in kj mol 1? C C(s, graphite) C(s, diamond) 5 The standard enthalpy change of neutralization when an acid reacts with an alkali is the number of kilojoules released by the C formation of one mole of salt. formation of one mole of water. neutralization of one mole of acid. neutralization of one mole of alkali.

4 6 Consider the following bond enthalpy values. For the reaction the enthalpy change, in kj mol 1, is C ond ond enthalpy / kj mol 1 O O +146 O H +463 O O +496 H O O H(g) H O H(g) + ½O O(g) 7 Using the data in the table below, calculate the standard enthalpy change, in kj mol 1, for the reaction between carbon disulfide, CS 2, and oxygen shown in the following equation. CS 2 (g) + 3O 2 (g) CO 2 (g) + 2SO 2 (g) Substance Standard enthalpy change of formation, H f / kj mol 1 CS 2 (g) +110 CO 2 (g) 390 SO 2 (g) C

5 8 The reaction for which the enthalpy change is the standard enthalpy change of formation of water, H, is f,298 H 2 (g) + ½O (g) H O(l) 2 2 H 2 (g) + ½O (g) H O(g) 2 2 C 2H 2 (g) + O (g) 2H O(l) 2 2 2H 2 (g) + O (g) 2H O(g) Which equation represents the reaction for which the enthalpy change, H, is the mean bond energy of the C-F bond? CF 4 (g) C(g) + 4F(g) ¼CF 4 (g) ¼C(g) + F(g) C C(g) + 4F(g) CF 4 (g) ¼C(g) + F(g) ¼CF 4 (g) 10 Given the following information CH 4 (g) C(g) + 4H(g) H = +Q kj mol 1 the mean bond enthalpy for the C H bond in methane is +Q +Q/4 C Q Q/4

6 11 Consider the following information: For the reaction the enthalpy change, in kj mol 1, is C ond ond enthalpy / kj mol 1 H H +436 I I +151 H I +299 H (g) + I (g) 2HI(g) The equation for the complete combustion of butanone, C 2 H 5 COCH 3, is C 2 H 5 COCH 3 (l) + 5½O 2 (g) 4CO 2 (g) + 4H 2 O(l) H = 2440 kj mol 1 Substance H f / kj mol 1 CO 2 (g) 394 H 2 O(l) 286 From the above data, the standard enthalpy change of formation of butanone, in kj mol 1, is C

7 13 In an experiment to determine the enthalpy change of combustion of an alcohol, a spirit burner containing the alcohol was weighed, lit and placed under a copper can containing a known volume of water. The temperature rise of the water was measured and the burner re-weighed. The enthalpy change calculated from the results was much less exothermic than the value reported in the literature. Which of the following factors is most likely to be the cause of this error? Heat loss around the side of the copper can. The use of a thermometer with a range of C rather than 0 50 C. C The use of a measuring cylinder for measuring the water rather than a pipette. Evaporation of the alcohol during the weighing. 14 The standard enthalpy changes of formation of carbon dioxide and of methanoic acid are 1 1 respectively. Calculate the enthalpy change for the reaction H 2 (g) + CO 2 (g) HCOOH(l) 1 1 C For which of the following changes is the value of H negative? K(g) K + (g) + e K + Cl (s) K + (g) + Cl (g) C Cl(g) + e Cl (g) Cl 2 (g) 2Cl(g)

8 16 The enthalpy change for the reaction between hydrochloric acid and sodium hydroxide is 56 kj mol 1. Therefore C the reaction is exothermic and the temperature rises. the reaction is exothermic and the temperature falls. the reaction is endothermic and the temperature rises. the reaction is endothermic and the temperature falls. 17 For which of the following reactions is the enthalpy change equal to the bond enthalpy of H I? HI(g) ½H 2 (g) + ½I 2 (s) HI(g) ½H 2 (g) + ½I 2 (g) C HI(g) H(g) + I(g) HI(g) H + (g) + I (g) 18 The equation for the complete combustion of pentane is C 5 H 12 (g) + 8O 2 (g) 5CO 2 (g) + 6H 2 O(l) H c 3509 kj mol 1 The standard enthalpy change of formation of CO 2 (g) is 394 kj mol 1 and that of H 2 O(l) is 286 kj mol 1. The standard enthalpy change of formation of pentane (in kj mol 1 ) is 5( 394) + 6( 286) + ( 3509) 5( 394) + 6( 286) ( 3509) C 5( 394) 6( 286) + ( 3509) 5( 394) 6( 286) ( 3509)

9 19 Which of these diagrams correctly represents an endothermic reaction? Enthalpy Reactants Enthalpy Reactants ΔH ve Products ΔH +ve Products C Enthalpy Products Enthalpy Products ΔH ve ΔH +ve Reactants Reactants

10 20 Some mean bond enthalpy values are given in the table below. ond Mean bond enthalpy / kj mol 1 H H +436 I I +151 H I +299 What is the enthalpy change for the reaction shown below in kj mol 1? = +288 H 2 (g) + I 2 (g) 2HI(g) = 288 C (2 299) (2 299) = In an experiment to measure the enthalpy change of a reaction involving gases, which of the following conditions must always be kept constant? C Pressure Temperature Volume Temperature and pressure

11 22 In an endothermic reaction in aqueous solution, which of the following is correct? Temperature Sign of enthalpy change Increases Positive Increases Negative C ecreases Positive ecreases Negative 23 The enthalpy change for the reaction to form hydrated sodium thiosulfate crystals cannot be measured directly. The following Hess cycle can be used. H r Na 2 S 2 O 3 (s) + 5H 2 O(l) Na 2 S 2 O 3.5H 2 O(s) +aq H 1 H +aq 2 Na 2 S 2 O 3 (aq) The enthalpy change for the reaction, H r, is equal to H 1 + H 2 H 1 H 2 C H1 H 2 H 1 + H 2

12 24 When 10 cm 3 of 2 mol dm 3 hydrochloric acid is reacted with 10 cm 3 of 2 mol dm 3 sodium hydroxide solution, the temperature change is T. HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) When the reaction is repeated with 50 cm 3 of each solution, the temperature change is T 5 T 1 C 5 T 10 2 T 25 Energy is evolved when one mole of gaseous calcium ions is hydrated. Ca 2+ (g) + aq Ca 2+ (aq) This reaction is more exothermic than the corresponding value for barium ions, a 2+, because the ionization energy of calcium is greater than that of barium. lattice energy of calcium oxide is more exothermic than that of barium oxide. C solubility of calcium hydroxide in water is less than that of barium hydroxide. ionic radius of Ca 2+ is less than that of a 2+.

13 26 In an experiment performed to measure the enthalpy change for the reaction Cu (aq) 3.0 g of zinc powder (an excess) was added to 30.0 cm 3 of copper(ii) sulfate solution of concentration 1.00 mol dm 3. The temperature rise of the mixture was 47.6 K. ssuming that the heat capacity of the solution is 4.2 J K 1 g 1, the enthalpy change for the reaction is given by H H C H H 27 The enthalpy change for the reaction C(s, graphite) + ½O 2 (g) CO(g) cannot be measured directly since some carbon dioxide is always formed in the reaction. It can be calculated using Hess s Law and the enthalpy changes of combustion of graphite and of carbon monoxide. C(s, graphite) + O 2 (g) CO 2 H 1 CO(g) + ½O 2 (g) CO 2 H 1 The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is 1 1 C 1 1

14 28 1. C 3 H 8 C 4 H 10 C 5 H 12 C 6 H C 7 H 16 C 8 H 18 C C 9 H 20 C 10 H If the mean C H bond enthalpy is +x, which of the following represents a process with an enthalpy change of +4x? C(g) + 4H(g) CH 4 (g) CH 4 (g) C(g) + 4H(g) C CH 4 (g) C(s, graphite) + 2H 2 (g) C(s, graphite) + 2H 2 (g) CH 4 (g) 30 The enthalpy change for the reaction CH 4 (g) C(g) + 4H(g) is kj mol 1. Hence the mean bond enthalpy for the C H bond is kj mol kj mol 1 C kj mol kj mol 1

15 31 Which equation represents the reaction for which the enthalpy change is the standard enthalpy change of formation, H f, of sodium nitrate, NaNO 3? C 2Na(s) + N 2 (g) + 3O 2 (g) 2NaNO 3 (s) Na(s) + ½N 2 (g) + 1½O 2 (g) NaNO 3 (s) Na(s) + N(g) + 3O(g) NaNO 3 (s) Na(g) + ½N 2 (g) + 1½O 2 (g) NaNO 3 (g) 32 Which equation represents the reaction for which the enthalpy change, H, is the mean bond enthalpy of the C H bond? C ¼CH 4 (g) ¼C(g) + H(g) CH 4 (g) C(s) + 2H 2 (g) CH 4 (g) C(g) + 4H(g) CH 4 (g) C(g) + 2H 2 (g)

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