2. Title: Lesson 4 The Equilibrium Law Learning Objectives: Know how to quantify K c using equilibrium concentrations Know how to determine K c when given initial concentrations using the ICE method Know how to determine equilibrium concentrations using K c

3. Main Menu The equilibrium law  So far we know how to derive the equilibrium constant K c and considered what the value tells us about the composition of an equilibrium mixture.  Now we will quantify these values...  We can use the equilibrium law to quantify equilibrium constant or the concentrations of reactants and products in an equilibrium.

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5. Quantifying concentrations of reactants or products from data on initial concentrations of other components  Step 1: Write the balanced equation.  Step 2: Under the equation, write the values of each component using three rows: initial, change, and equilibrium.  Step 3: Write the expression for K c from the balanced equation. Substitute values for equilibrium concentration and calculate K c. Initial – Change – Equilibrium = ICE method

6. ASG has a dance, and lets 100 boy-girl couples into the gym. Throughout the evening some couples have fights and break apart, forming single boys and single girls. Of course some of these singles form new couples. At the end of the evening there are 12 single girls. Calculate the equilibrium numbers. 1 Couple  1 girl + 1 boy Initial 100 0 0 Let’s start with a silly, non-chem example…

7. ASG has a dance, and lets 100 couples into the gym. Throughout the evening some couples have fights and break apart, forming single boys and single girls. Of course some of these singles form new couples. At the end of the evening there are 12 single girls. Calculate the equilibrium numbers. 1 Couple  1 girl + 1 boy Initial 100 0 0 12 Equilibrium

8. ASG has a dance, and lets 100 couples into the gym. Throughout the evening some couples have fights and break apart, forming single boys and single girls. Of course some of these singles form new couples. At the end of the evening there are 12 single girls. Calculate the equilibrium numbers. 1 Couple  1 girl + 1 boy Initial 100 0 0 Change -12+12 12 88 Equilibrium

9. ASG has a dance, and lets 100 couples into the gym. Throughout the evening some couples have fights and break apart, forming single boys and single girls. Of course some of these singles form new couples. At the end of the evening there are 12 single girls. Calculate the equilibrium numbers. Equilibrium 88 12 12 1 Couple  1 girl + 1 boy = 1.64

10. Example: 4 moles of H 2 gas and 6 moles of Cl 2 gas are pumped into a 2 liter tank at 30  C. At some time later, it is found that there are 2 moles of HCl gas in the tank. Calculate the Equilibrium Constant. H 2 + Cl 2  2HCl

11. Example: 4 moles of H 2 gas and 6 moles of Cl 2 gas are pumped into a 2 liter tank at 30  C. At some time later, it is found that there are 2 moles of HCl gas in the tank. Calculate the Equilibrium Constant. Initial Concentration H 2 + Cl 2  2HCl 0

12. Example: 4 moles of H 2 gas and 6 moles of Cl 2 gas are pumped into a 2 liter tank at 30  C. At some time later, it is found that there are 2 moles of HCl gas in the tank. Calculate the Equilibrium Constant. Initial Concentration H 2 + Cl 2  2HCl 0[2]

13. Example: 4 moles of H 2 gas and 6 moles of Cl 2 gas are pumped into a 2 liter tank at 30  C. At some time later, it is found that there are 2 moles of HCl gas in the tank. Calculate the Equilibrium Constant. Initial Concentration H 2 + Cl 2  2HCl Change Equilibrium Conc. 0[2][3]

14. Example: 4 moles of H 2 gas and 6 moles of Cl 2 gas are pumped into a 2 liter tank at 30  C. At some time later, it is found that there are 2 moles of HCl gas in the tank. Calculate the Equilibrium Constant. Initial Concentration H 2 + Cl 2  2HCl Change Equilibrium Conc. 0[2][3] [1] +1- ½ [1.5][2.5] = 0.267  0.3 The changes that occur must be in the same ratio as the co-efficients in the balanced equation

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17. Calculating equilibrium concentrations from the equilibrium constant

18. Main Menu More complex when you’re only given K c and initial concentrations... Continued on next slide...

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20. Calculating equilibrium concentrations when K c is very small...  In some reactions Kc is very small, less than 10 -3.  This represents a reaction in which the forward reaction has hardly proceeded.

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23. Solutions

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