ACSBR 18E Energy Changes (Extensions) - Assignment

Anglo-Chinese School (Barker Road) A Methodist Institution Founded in 1886 CHEMISTRY DEPARTMENT OF SCIENCE Name: ( ) Class: SEC 4 ENERGY CHANGES (EXTENSIONS) – ASSIGNMENT ALEX LEE & SHERRI TAN/2010 PAGE 1 OF 8 PURE Multiple-Choice Questions [20 Marks] TOTAL SCORE / 30 Write in your selected answer for the multiple-choice questions in the boxes provided. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1. What is meant by an ‘endothermic’ reaction? A A catalyst is needed for the reaction to take place. B Light energy is absorbed during the reaction. C The reactants have less energy than the products of the reaction. D They are chemical reactions which require heat to start. 2. A pupil added 0.06 mol of sodium nitrate to 100 cm3 o f w a t e r a t 2 0 . 0 °C. The enthalpy change of solution of sodium nitrate is +20.5 kJ/mol. After dissolving the solute, the temperature of the solution will be about A 18.0 °C B 20.0 °C C 23.0 °C D 26.0 °C 3. Early photographers used the oxidation of magnesium powder to produce flashes of light in the presence of oxygen from the air. Magnesium reacts according to the equation: 2 Mg (s) + O2 (g) ⎯→ 2 MgO (s) ΔH = – 2400 kJ/mol When 0.24 g of magnesium reacts with excess oxygen, the energy released would be A 3.00 kJ B 6.00 kJ C 12.0 kJ D 24.0 kJ 4. The combustion of octane, C8H18, can be expressed in the equation below. 2 C8H18 (l) + 25 O2 (g) ⎯→ 16 CO2 (g) + 18 H2O (g) Given that combusting 57 grams of octane results in x kJ of energy being evolved, what is the enthalpy change for the above reaction? A + x kJ B + 2x kJ C – 0.5x kJ D – 4x kJ

ALEX LEE & SHERRI TAN/2010 PAGE 2 OF 8 5. The hydration of quicklime to become slaked lime is an exothermic reaction, and can be expressed in the following equation: CaO (s) + H2O (l) ⎯→ Ca(OH)2 (s) ΔH= – 65.2 kJ/mol An unknown mass of quicklime was reacted as above. Given that the mass of the quicklime increased by 37.3 grams in the reaction, calculate the energy evolved. A 32.9 kJ B 43.4 kJ C 65.2 kJ D 135 kJ 6. Hydrogen reacts with chlorine. H2 (g) + Cl2 (g) ⎯→ 2 HCl (g) ΔH= – 184 kJ/mol Why does the enthalpy change for this reaction have a negative sign? A Hydrogen and chlorine are covalent, but hydrogen chloride is ionic. B More bonds are formed than are broken. C The speed of the reaction increases as temperature increases. D The total energy of bond breaking is less than that of bond forming. 7. The energy l e v e l d i a g r a m f o r t h e r e a c t i o n b e t w e e n a q u e o u s s o d i u m h y d r o x i d e and dilute hydrochloric acid is shown. What can be deduced from the diagram? A The OH- ions have more energy than the H+ ions. B The products contain less energy than the reactants. C The reaction has a high activation energy. D The reaction occurs readily at room temperature. 8. A series of chemical reactions are represented in the energy level diagram below. Given that x, y and z are positive numbers, the enthalpy change of the overall reaction is Energy Progress of Reaction H+ (aq) + OH- (aq) H2O (l) H = – 54 kJ/mol Energy Progress of Reaction x y z

ALEX LEE & SHERRI TAN/2010 PAGE 3 OF 8 A (x + y) – z B x – (y + z) C x + y + z D y + z 9. The reaction between chlorine and methane can be expressed as four steps: Step I: Cl2 (g) ⎯→ 2 Cl (g) H = + 243 kJ/mol Step II: Cl (g) + CH4 (g) ⎯→ CH4Cl (g) H = – 330 kJ/mol Step III: CH4Cl (g) ⎯→ CH3Cl (g) + H (g) H = + 413 kJ/mol Step IV: H (g) + Cl (g) ⎯→ HCl (g) H = – 432 kJ/mol Using the information provided above, what is the enthalpy change of the overall reaction, Cl2 (g) + CH4 (g) ⎯→ CH3Cl (g) + HCl (g)? A + 137 kJ/mol B – 106 kJ/mol C – 228 kJ/mol D – 455 kJ/mol 10. Which of the following energy profile diagrams shows the fastest exothermic reaction? A C B D 11. In the energy profile diagram below, which represents the enthalpy change and the activation energy respectively? enthalpy change activation energy A p q B q q + (r – p) C r q D r – p q + (r – p) Energy Progress of Reaction p q r Energy Reaction Pathway Energy Reaction Pathway Energy Reaction Pathway Energy Reaction Pathway

ALEX LEE & SHERRI TAN/2010 PAGE 4 OF 8 12. When glucose is dissolved into water, attractive forces are initially formed between the glucose molecules and the water molecules. As more water is added, these attractive forces are gradually broken. Which of the following g r a p h s s h o w s h o w t h e t e m p e r a t u r e o f t h e resulting solution varies as water is added? A C B D 13. The formation of ethanol from ethane and steam is shown in the following equation: C2H4 (g) + H2O (g) C2H5OH (g), ΔH = – 50 kJ/mol Under which conditions would the above reaction provide the greatest yield? temperature pressure A high temperature high pressure B high temperature low pressure C low temperature high pressure D low temperature low pressure 14. The production of synthetic diamonds is very difficult although the conversion of graphite into diamond is only very slightly endothermic. C (graphite) ⎯→ C (diamond) ΔH = +2.1 kJ/mol Which of the following help to explain this observation? (i) The activation energy of the reaction is large. (ii) An equilibrium exists between diamond and graphite. (iii) Only exothermic reactions can be made to occur readily. A (i) only B (ii) only C (i) and (iii) only D (ii) and (iii) only temperature volume of water added temperature volume of water added temperature volume of water added temperature volume of water added

ALEX LEE & SHERRI TAN/2010 PAGE 5 OF 8 15. Which of the following statements about reversible reactions is true? A A higher temperature increases the speed of all reversible reactions. B Endothermic reversible reactions obtain a greater yield under low temperatures. C Exothermic reversible reactions occur the fastest under low temperatures. D Reversible reactions do not require activation energy to occur. 16. Which of the following statements pertaining to catalysts is true? A A catalyst decreases the enthalpy change of an endothermic reaction. B A catalyst increase the yield of reversible reaction. C A catalyst remains physically unchanged throughout the chemical reaction. D A catalyst increases the speed of both the forward and backward reactions. 17. The energy profile diagram of a chemical reaction is shown below. Which of the following shows how the energy profile diagram of a reaction would change when a catalyst is added to the reaction vessel? A C B D 18. A metal M was placed in aqueous copper(II) nitrate. A reddish-brown solid was obtained, and the temperature of the reaction mixture rose. Which of the following conclusions cannot be deduced from this information? A M has the same valency as copper. C M is more reactive than copper. B M has been oxidised. D The reaction is exothermic. Energy Level Progress of Reaction Energy Level Progress of Reaction Energy Level Progress of Reaction Energy Level Progress of Reaction Energy Level Progress of Reaction

ALEX LEE & SHERRI TAN/2010 PAGE 6 OF 8 19. Consider the following bond energies. Type of Bond kJ mol-1 C – C 346 C – H 410 Si – Si 176 Si – H 318 Which of the following statements could be considered to be consistent with these values? A 346 kJ is the amount of energy evolved when 1 mole of graphite sublimes. B Methane, CH4, is chemically more stable than silane, SiH4. C The C – C bond is less stable than the Si – Si bond. D The Si – Si bond is the least readily broken among all. 20. Consider the chemical reaction below, which has an enthalpy change of –117 kJ mol-1. H Cl ⏐ ⏐ H