As Chemistry Prep 2 7 Chemical Equilibria

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As Chemistry Prep 2 7 Chemical Equilibria

  1. 1. AS Chemistry prep - 2.7 ‘Chemical equilibria’ • This sheet of problems is designed to help you learn and understand the material we cover in class. • In addition to attempting these problems you should be reading around the topic, which is covered by pages 202-207 in your textbooks. • We will be spending one week on this topic before half-term. I would ideally like your answers before the end of school on Friday; however, if you wish to spend some of your time over the break doing working on this… Exercise 1 - Key terms Find and explain the meanings of the following terms from this topic: 1. Reversible reaction 2. Dynamic equilirium 3. Position of equilibrium 4. Le Chetalier’s principle Exercise 2 - The Haber- Bosch process Answer the following questions on the industrial fixation of atmospheric nitrogen: N2(g) + 3H2(g) ⇌ 2NH3(g) 1. Under certain conditions 1 mole of nitrogen and 3 moles of hydrogen were mixed and 20% of the gases reacted. Sketch three graphs, on the same axes, showing the number of moles for each of nitrogen, hydrogen and ammonia. 2. Describe and explain the ‘compromise’ conditions used for the Haber-Bosch process. Exercise 3 - Predicting changes in the position of equilibrium Read the following questions carefully, be sure to explain your answers fully: 1. Nickel is purified by passing carbon monoxide over the heated metal. A gaseous nickel compound, [Ni(CO)4] is formed: Ni(s) + 4CO(g) ⇌ [Ni(CO)4](g) ∆H = -161 kJ/mol What will the effect of increasing temperature be on this equilibrium? 2. Alcohols react reversibly with carboxylic acids to produce an ester plus water. Predict the effect of increasing the temperature on the position of equilibrium if this esterification reaction: C2H5OH(l) + CH3COOH(l) ⇌ CH3COOC2H5(l) + H2O ∆H = 0 kJ/mol 3. Predict the effect of increasing pressure on the position of equilibrium of the reaction in Q1. 4. Gaseous carbon dioxide dissolves in water and forms a solution of carbonic acid: CO2(g) + H2O(l) ⇌ H2CO3(aq) Carbon dioxide is more soluble in hot water. Explain whether ∆H for the above reaction is exothermic or endothermic. 5. Predict whether the position of equilibrium moves to the left, right or stays the same when the pressure on each of the following is increased: a. 2O3(g) ⇌ 3O2(g) b. C(s) + H2O(g) ⇌ CO(g) + H2(g) c. 4NH3(g) 5O2(g) ⇌ 4NO(g) + 6H2O(g) 6. Match the conditions to the reaction: A 750 °C, nickel catalyst B 420 °C, vanadium catalyst 1 CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ∆H = +206 kJ/mol 2 SO2(g) + ½ O2 ⇌ SO3(g) ∆H = -98 kJ/mol
  2. 2. 7. Explain the use of catalysts in reactions like the Haber-Bosch process and reaction 2 in the above question. 8. Lead chloride is an insoluble solid. When dilute hydrochloric acid is added to it, the following equilibrium reaction occurs: PbCl2(s) + 2Cl-(aq) ⇌ PbCl42-(aq) The position of the equilibrium is to the left so most of the lead chloride is present as a solid. Predict what would happen if concentrated hydrochloric acid were added.

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