CHEMICAL EQUILIBRIUM

Chemical Equilibrium-PDF Download

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A change in the concentration of one of the species in an equilibrium system will cause a stress. on the system, 1 If additional reactant N2 is added it creates a stress on the equilibrium system The. equilibrium shifts to the right to consume N2 and H2 simultaneously producing more. NH3 Consequently at the new equilibrium position there is a greater concentration of. NH3 than in the original equilibrium mixture, 2 If N2 were removed from the system the equilibrium shifts to the left to produce more N2. and H2 simultaneously reducing the concentration of NH3. 3 If additional NH3 is added to the equilibrium mixture the equilibrium shifts to the left. The new equilibrium mixture would have a greater concentration of N2 and H2 than the. original equilibrium mixture, In industry the yield of NH3 is increased by removing NH3 as it is formed. In ionization reactions the shift in equilibrium upon addition of more of one of the ions. is termed the common ion effect Consider the equilibrium. AgC2H3O2 s Ag aq C2H3O2 aq, If additional acetate ion C2H3O2 is added then LeCh telier s principle predicts the equilibrium. will shift to the left If we start with a saturated solution of AgC2H3O2 precipitation of. AgC2H3O2 s should occur On the other hand if we add a substance that contains no common. ion nor does it react with any of the equilibrium species we would expect no effect on the. equilibrium, Another type of stress that can be applied to an equilibrium system is heat Changing the.
temperature of an equilibrium reaction mixture corresponds to adding or removing heat from a. If the forward reaction is exothermic that is it releases heat an increase in temperature. will cause the equilibrium to shift to the left If the forward reaction is endothermic that is it. absorbs heat an increase in temperature will cause the equilibrium to shift to the right The. synthesis of ammonia is exothermic,N2 g 3H2 g 2NH3 g heat. An increase in the temperature causes NH3 to decompose The equilibrium shifts to the left. Thus the concentration of N2 and H2 increases going toward the new equilibrium state These. results are predicted by LeCh telier s principle which indicates that if we raise the temperature. of a system a reaction occurs which absorbs heat thereby minimizing the effect of the. temperature increase, The forward and reverse reactions are usually shown together in a single equation using a double. arrow and if the forward reaction is endothermic the reverse reaction is exothermic and vice. endothermic,More generally X Y,exothermic,Summary of Changes on Equilibrium. Condition Change Stress Shift in the direction of, Concentration Add a reactant Products forward reaction. Remove a product Products forward reaction,Add a product Reactants reverse reaction.
Temperature Endothermic Reaction,Raise T Products forward reaction to. remove heat,Lower T Reactants reverse reaction to,Exothermic Reaction. Raise T Reactants reverse reaction to,remove heat,Lower T Products forward reaction to. Catalyst Increase rates equally No effect,SAFETY AND WASTE DISPOSAL. Wear gloves for this experiment All waste is to be placed in the Inorganic Waste. Container located in the fumehood, Note The symbol in parentheses appearing after each substance in the chemical.
equation describes the state of the substance The symbol g refers to a gas l to. a liquid s to a solid and aq means that the substance is dissolved in aqueous. Part A The Chromate Dichromate Equilibrium,The equation for this equilibrium is. 2CrO42 aq 2H aq Cr2O72 aq H2O l,yellow orange, 1 Add about 3 mL of 0 1M potassium chromate solution K2CrO4 to a clean test tube 20. drops is approximately 1mL, Record the color of the solution on the Data Sheet 1. 2 Add several drops of 3M sulfuric acid H2SO4 until a change is observed. Record observations on the Data Sheet 2 Note H2SO4 is a source of H aq. 3 Using a clean test tube split your solution into two equal halves One test tube will be. used as a control, 4 Add 1 M sodium hydroxide solution NaOH drop wise to the solution in one of the test. tube until a change occurs Note NaOH will reduce the concentration of H aq. Record observations on the Data Sheet 3, 5 Explain the results in terms of Le Ch teliers Principle.
Part B The Cobalt II Ion Equilibrium,The equation for this equilibrium is. Co H2O 62 aq 4Cl aq CoCl42 aq 6H2O l, 5 Add about 1 mL of 0 1 M cobaltous chloride or cobalt II chloride solution CoCl2 to a. clean test tube, Record the color of the solution on the Data Sheet 6. 6 Under the fume hood add several drops of concentrated hydrochloric acid HCl to the. solution in the test tube until a change is noted,Record observations on the Data Sheet 7. 7 Add distilled water to the solution until a change is noted Do not discard this solution. It will be used in Part C, NOTE If the addition of water changes the position of the equilibrium it is due to the.
dilution of the chloride Cl ion and not an increase in the amount of water. Record observations on the Data Sheet 8, 8 Explain the results in terms of Le Ch teliers Principle. Part C Effect of Temperature on the Cobalt II Ion Equilibrium. The equation for this equilibrium H 50 kJ mole is,Co H2O 62 aq 4Cl aq heat CoCl42 aq 6H2O l. 9 Using a test tube clamp place the test tube from Part B Step 7 in a hot water bath. without spilling its contents Heat the solution until a change is observed. 10 Record the color of the hot solution on the Data Sheet 11. 11 Remove the test tube from the hot water bath and allow it to cool Prepare an ice bath by. filling a 250 mL beaker with ice and water Insert the test tube into the ice bath. 12 Record the color of the cold solution on the Data Sheet 12. 13 Answer question 13 and explain the results in terms of Le Ch teliers Principle. Part D Saturated Ammonium Chloride Equilibrium,The equation for this equilibrium is. NH4Cl s NH4 aq Cl aq, 14 Add about 3 mL of saturated ammonium chloride solution NH4Cl to a clean test tube. 15 Under the fume hood add several drops of concentrated HCl to the solution in the test. tube until a change is observed,Record observations on the Data Sheet 15.
16 Using a test tube clamp heat the test tube and contents from Step 15 in a hot water bath. until a change is observed Stir the solution with a stirring rod while heating. Record observations on the Data Sheet 16 Discard the contents of the test tube. 17 Add enough crystals of solid NH4Cl to cover the bottom of a clean test tube Add about 5. mL of distilled water to the solid NH4Cl in the test tube. Feel the test tube to determine if the dissolution of NH4Cl produces a temperature. Record observations on the Data Sheet 17, 18 Answer question 18 and explain the results in terms of Le Ch teliers Principle. Chemical Equilibrium Quiz Hints be able to answer questions like the following. 1 In an aqueous solution of sodium carbonate Na2CO3 the following equilibrium occurs. CO32 aq H2O l HCO3 aq OH aq, a How would the addition of solid sodium hydrogen carbonate NaHCO3 affect the. equilibrium Explain your answer, b If a small volume of HCl solution were added how would the equilibrium be. changed Explain your answer, 2 Carbon monoxide CO and hydrogen H2 gases are produced if water vapor is passed. over carbon graphite,C s H2O g CO g H2 g, The reaction is endothermic If the temperature is increased how will the equilibrium be.
affected Explain your answer, 3 If a saturated solution of sodium nitrate NaNO3 is prepared the following equilibrium. NaNO3 s Na aq NO3 aq, a If nitric acid is added to the saturated solution what will happen to the. equilibrium Explain your answer, b The dissolution of NaNO3 is endothermic What change in conditions would. cause more NaNO3 s to dissolve Explain your answer. 4 One step in the production of sulfuric acid involves the equilibrium. 2SO2 g O2 g 2SO3 g, The reaction is exothermic At equilibrium only about 80 of the SO2 is converted to. SO3 Suggest two ways the equilibrium yield of SO3 might be increased. 7 Add distilled water to the solution until a change is noted Do not discard this solution It will be used in Part C NOTE If the addition of water changes the position of the equilibrium it is due to the dilution of the chloride Cl ion and not an increase in the amount of water Record observations on the Data Sheet 8 8 Explain the

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