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Chemistry 12 (HL) Unit 4 / IB Topic 7.2 Chemical Equilibrium 4 Industrial Processes – Haber Process and Contact Process Reference: Higher Level Chemistry, p. 248-251 The industrial production of chemical substances requires careful planning. Chemical engineers need to consider 2 criteria when designing a process to produce any chemical: 1. How can the yield be maximized? (Think about how you would use Le Chatelier’s Principle to do this.) 2. How can the rate be maximized? (Think about the factors that affect the rate of a chemical reaction.) In many industrial processes, these two criteria are at odds with each other, and compromises must be made. e.g. 90% yield and a reaction time of one year vs 50% yield and a reaction time of several days THE HABER PROCESS (aka The Haber Bosch Process) The Haber process was developed by the German chemist Fritz Haber in 1913. This process is used to manufacture used to make: , which is • F • E • P The chemical equation for this reaction is: This reaction does not readily occur in nature because …. p. 1 Chemistry 12 (HL) Unit 4 / IB Topic 7.2 How can Le Chatelier’s Principle and kinetics be applied in order to maximize the yield of ammonia? 1. concentration reactants products 2. pressure equilibrium considerations: kinetics (rate) considerations: economic factors: 3. temperature equilibrium considerations: kinetics (rate) considerations: the compromise: 4. catalyst p. 2 Chemistry 12 (HL) Unit 4 / IB Topic 7.2 Interpret this graph showing the effects of reaction conditions on the yield of ammonia: Source: http://www.ausetute.com.au/haberpro.html A summary of the Haber Process: Source: http://www.chemguide.co.uk/physical/equilibria/haber.html Typical yield of the Haber process: p. 3 Chemistry 12 (HL) Unit 4 / IB Topic 7.2 THE CONTACT PROCESS The Contact Process is used to manufacture which is used for: , • Fe • Po • De • Pa • Me • Ba There are 3 reactions involved in this process: 1 combustion of sulfur 2 oxidation of sulfur dioxide 3 combination of sulfur trioxide with water The overall rate of the process depends on the STEP 2. We can apply Le Chatelier’s Principle to this reaction to find the conditions that most favour the formation of the product. 2 SO2(g) + O2(g) ⇔ 2 SO3(g) ∆H = - 196 kJ mol-1 1 pressure 2 temperature 3 catalyst p. 4 Chemistry 12 (HL) Unit 4 / IB Topic 7.2 Here is a summary diagram of this step in the Contact Process: Source: http://www.chemguide.co.uk/physical/equilibria/contact.html QUESTIONS 1. N2(g) + 3H2(g) ⇔ 2NH3(g) In the reaction ∆H = –92 kJ which of the following changes will increase the amount of ammonia at equilibrium? I. Increasing the pressure II. Increasing the temperature III. Adding a catalyst A. 2. I only B. II only 2 SO2(g) + O2(g) ⇔ 2 SO3(g) C. I and II only D. II and III only ∆H = -200 kJ According to the equation above, what temperature and pressure conditions produce the greatest amount of SO3? temperature pressure A low low B low high C high high D high low p. 5 Chemistry 12 (HL) Unit 4 / IB Topic 7.2 3. The diagrams below represent equilibrium mixtures for the reaction Y + X2 XY + X at 350 K and 550 K respectively. Deduce and explain whether the reaction is exothermic or endothermic. 3. Consider the following reaction in the Contact process for the production of sulfuric acid for parts (a) to (d) in this question. 2SO2 + O2 ⇔ 2SO3 (a) Write the equilibrium constant expression for the reaction. (1) (b) (i) State the catalyst used in this reaction of the Contact process.(1) ii) State and explain the effect of the catalyst on the value of the equilibrium constant and on the rate of the reaction. (4) (c) Use the collision theory to explain why increasing the temperature increases the rate of the reaction between sulfur dioxide and oxygen. (2) (d) Using Le Chatelier’s principle state and explain the effect on the position of equilibrium of (i) increasing the pressure at constant temperature. (2) (ii) removing of sulfur trioxide. (2) (iii) using a catalyst. (2) p. 6