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 tem