1. Altering Solubility #2 Effect of Temperature Here we’ll have a look at how changes in temperature affect the solubility of a compound.

2. How temperature affects the solubility of a compound depends on whether dissolving the compound is:

3. Endothermic or Endothermic, or

4. How temperature affects the solubility of a compound depends on whether dissolving the compound is: Endothermic or Exothermic Exothermic. We’ll do a couple of examples to illustrate this.

5. Barium sulphate (BaSO4), is known to dissolve endothermically in water. It is known that barium sulphate (BaSO 4 ) dissolves endothermically.

6. Its solubility equilibrium equation… It is known that barium sulphate (BaSO 4 ) dissolves endothermically. Its solubility equilibrium equation

7. can be written like this, with the solid BaSO4 on the left… It is known that barium sulphate (BaSO 4 ) dissolves endothermically. Its solubility equilibrium equation can be written like this:

8. the dissolved ions on the right… It is known that barium sulphate (BaSO 4 ) dissolves endothermically. Its solubility equilibrium equation can be written like this:

9. And because it’s endothermic, and heat is being consumed, the heat term is written on the Left side of the arrow. It is known that barium sulphate (BaSO 4 ) dissolves endothermically. Its solubility equilibrium equation can be written like this:

10. When the temperature of a system is increased, it means heat is added to this endothermic system. When the temperature is increased, heat is added to the system

11. According to Le Chatelier’s Principle, the system can compensate for the added heat by shifting away from the heat term in order to use up the excess heat. When the temperature is increased, heat is added to the system

12. In this case the heat term is on the left, so it causes a shift to the right. When the temperature is increased, heat is added to the system This will cause a shift to the RIGHT

13. Which occurs like this Shift right

14. We see that as a result of shifting to the right, the concentrations of the dissolved ions have increased. Concentrations of the dissolved ions have increased Shifted to the RIGHT

15. And the mass of the solid BaSO4 present has decreased. The mass of solid BaSO 4 has decreased Shifted to the RIGHT

16. So because a shift to the right caused the mass of the solid to decrease and the concentration of dissolved ions to increase, we can say that.. The mass of solid BaSO 4 has decreased Shifted to the RIGHT Concentrations of the dissolved ions have increased

17. As a result of shifting to the right the solubility of BaSO4 has increased. The mass of solid BaSO 4 has decreased Shifted to the RIGHT The solubility of BaSO 4(s) has INCREASED. Concentrations of the dissolved ions have increased

18. So we can summarize by saying that increasing the temperature of a solution of a compound that dissolves endothermically… Increasing the temperature of a solution of a compound that dissolves endothermically…

19. Causes the solubility equilibrium to shift to the right… Causes a shift to the RIGHT… Increasing the temperature of a solution of a compound that dissolves endothermically…

20. Which increases the solubility of the solid compound. Causes a shift to the RIGHT… Which INCREASES the solubility of the solid compound Increasing the temperature of a solution of a compound that dissolves endothermically…

21. It should be easy to see now, that if we were to decrease the temperature of this endothermic system… When the temperature is DECREASED, heat is removed from the system

22. It would mean that we are removing heat from the system. In order to compensate for the loss of heat… When the temperature is DECREASED, heat is removed from the system

23. Le Chatelier’s Principle would predict that this equilibrium would shift to the left in order to produce more heat. A shift to the left… When the temperature is DECREASED, heat is removed from the system This will cause a shift to the LEFT

24. Would increase the mass of undissolved solid… A shift to the LEFT

25. And decrease the concentrations of the dissolved ions. A shift to the LEFT

26. In other words, a shift to the left causes the solubility to decrease. A shift to the LEFT Causes the solubility to DECREASE

27. So we can summarize by saying that decreasing the temperature of a solution of a compound that dissolved endothermically… Decreasing the temperature of a solution of a compound that dissolves endothermically…

28. Causes a shift to the left Causes a shift to the LEFT… Decreasing the temperature of a solution of a compound that dissolves endothermically…

29. Which decreases the solubility of the solid compound. Causes a shift to the LEFT… Which DECREASES the solubility of the solid compound Decreasing the temperature of a solution of a compound that dissolves endothermically…

30. Now let’s consider a compound that dissolves exothermically. It is known that calcium acetate [Ca(CH 3 COO) 2 ] dissolves exothermically. It is known that calcium acetate [Ca(CH 3 COO) 2 ] dissolves exothermically.

31. So its solubility equilibrium equation can be written like this, with the solid on the left It is known that calcium acetate [Ca(CH 3 COO) 2 ] dissolves exothermically. Its solubility equilibrium equation can be written like this:

32. The dissolved ions on the right It is known that calcium acetate [Ca(CH 3 COO) 2 ] dissolves exothermically. Its solubility equilibrium equation can be written like this:

33. And the heat term on the right. It is known that calcium acetate [Ca(CH 3 COO) 2 ] dissolves exothermically. Its solubility equilibrium equation can be written like this:

34. Let’s see what happens when we increase the temperature of a saturated solution of calcium acetate. An increase in temperature means that heat is added.

35. Increasing the temperature means we’re adding heat to the system. An increase in temperature means that heat is added.

36. According to Le Chatelier’s Principle, this will cause the equilibrium to shift to the left in order to use up some of the excess heat. This will cause a shift to the LEFT An increase in temperature means that heat is added.

37. A shift to the left occurs like this… Shift Left

38. We can see that as a result of the shift to the left, the concentrations of the dissolved ions have decreased. Concentrations of the dissolved ions have decreased Shifted to the LEFT

39. And the mass of solid calcium acetate in the container has increased. The mass of solid has increased Concentrations of the dissolved ions have decreased Shifted to the LEFT

40. Because there is more solid and less dissolved ions, we can say that the solubility of calcium acetate has decreased. The mass of solid has increased Concentrations of the dissolved ions have decreased Shifted to the LEFT The Solubility of calcium acetate has DECREASED

41. So we can summarize by saying that increasing the temperature of a solution of a compound that dissolves exothermically, which means adding heat to it… Increasing the temperature of a solution of a compound that dissolves exothermically An increase in temperature means that heat is added.

42. Causes the solubility equilibrium to shift to the left Causes a shift to the LEFT Increasing the temperature of a solution of a compound that dissolves exothermically

43. Which decreases the solubility Causes a shift to the LEFT Which DECREASES the solubility Increasing the temperature of a solution of a compound that dissolves exothermically

44. Now if we take a saturated solution of calcium acetate, a compound which dissolves exothermically and we Decrease the temperature… If we decrease the temperature of a solution of a compound that dissolves exothermically

45. It means we are removing heat from the system If we decrease the temperature of a solution of a compound that dissolves exothermically We are removing heat

46. This will cause this equilibrium to shift to the right. This will cause a shift to the RIGHT We are removing heat

47. Giving us this This will cause a shift to the RIGHT

48. As a result of shifting to the right, we can see that the concentrations of the dissolved ions have increased. This will cause a shift to the RIGHT Concentrations of the dissolved ions have increased

49. And the mass of the solid has decreased, so more of it has dissolved. This will cause a shift to the RIGHT The mass of solid has decreased Concentrations of the dissolved ions have increased

50. Because there is less solid and more dissolved ions, the solubility of calcium acetate has Increased This will cause a shift to the RIGHT The mass of solid has decreased Concentrations of the dissolved ions have increased The solubility of calcium acetate has INCREASED

51. So to summarize, if a compound dissolves exothermically and the temperature is Increased… So if a compound dissolves exothermically and the temperature is Increased…

52. The equilibrium will shift to the left So if a compound dissolves exothermically and the temperature is Increased… The equilibrium will shift LEFT

53. And the solubility will Decrease So if a compound dissolves exothermically and the temperature is Increased… The equilibrium will shift LEFT And the Solubility will DECREASE.

54. And if a compound dissolved exothermically and the temperature is Decreased So if a compound dissolves exothermically and the temperature is Decreased…

55. The solubility equilibrium will shift to the Right So if a compound dissolves exothermically and the temperature is Decreased… The equilibrium will shift RIGHT

56. And the solubility will Increase. So if a compound dissolves exothermically and the temperature is Decreased… The equilibrium will shift RIGHT And the Solubility will INCREASE.