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Unit 17 Daily 2. What is Le Chatelier’s Principle?

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Presentation on theme: "Unit 17 Daily 2. What is Le Chatelier’s Principle?"— Presentation transcript:

1 Unit 17 Daily 2

2 What is Le Chatelier’s Principle?

3 1. Explore factors affecting equilibrium 2. Predict direction of equilibrium shift 3. Predict resulting changes in concentration 4. Make equilibrium serve your own evil purposes

4 Equilibrium is a RATE balance. Anything that can affect the rate of the forward or reverse reaction can throw equilibrium off. What are the factors that affect reaction rate? 1) Concentration 2) Pressure or Volume (gases) 3) Temperature 4) Surface Area 5) Catalysts/Inhibitors

5 “If a system at equilibrium is subjected to an external stress, the equilibrium will shift to minimize the effects of that stress” The Steps of Le Chatelier’s Principle: 1) Stress: Adding or removing a reactant, adding or removing a product, changing the pressure, volume, or temperature. 2) Shift: The equilibrium will shift away from what is added and towards what is removed. 3) Change in Concentration: The concentration of what is being shifted towards increases, the concentration of what is being shifted away from decreases.

6 Fe 3+ (aq) + SCN - (aq)  FeSCN 2+ (aq) (colorless)(red) If more Fe 3+ is added to the system, what will happen? equilibrium shifts to the right equilibrium shifts to the product side the forward reaction is favored (forward shift) How are concentrations affected? [Fe 3+ ] increases, [SCN - ] decreases, [FeSCN 2+ ] increases How is K eq affected? K eq does not change when changes in concentration cause a shift in equilibrium

7 Fe 3+ (aq) + SCN - (aq)  FeSCN 2+ (aq) (colorless)(red) If more FeSCN 2+ is added to the system, what will happen? equilibrium shifts to the left equilibrium shifts to the reactant side the reverse reaction is favored (reverse shift) How are concentrations affected? [Fe 3+ ] increases, [SCN - ] increases, [FeSCN 2+ ] increases

8 Fe 3+ (aq) + SCN - (aq)  FeSCN 2+ (aq) (colorless)(red) If SCN - is removed from the system (by adding AgNO 3 so that AgSCN (s) precipitate forms), what will happen? equilibrium shifts to the left equilibrium shifts to the reactant side the reverse reaction is favored (reverse shift) How are concentrations affected? [Fe 3+ ] increases, [SCN - ] increases (but also decreases since it was removed), [FeSCN 2+ ] decreases

9 Only affect an equilibrium system if gases are present What is the relationship between moles of gas and volume/pressure? P = (nRT)/(V) If pressure is increased (or volume decreased): equilibrium will shift towards the side with FEWER moles of gas to bring the pressure back down If pressure is decreased (or volume increased): equilibrium will shift towards the side with MORE moles of gas to bring the pressure back up

10 N 2(g) + 3H 2(g)  2NH 3(g) (4 moles)(2 moles) If pressure is increased (volume decreased) on the system, what will happen? equilibrium shifts to the right equilibrium shifts to the product side the forward reaction is favored (forward shift) How are concentrations affected? [N 2 ] decreases, [H 2 ] decreases, [NH 3 ] increases

11 Notes: If the number of moles of gas are equal on both sides, then the equilibrium can’t shift H 2(g) + I 2(g)  2HI (g) Make sure to only count the moles of GAS when considering pressure effects on equilibrium

12 If temperature is increased in the system, what will happen? equilibrium will shift in the endothermic direction the endothermic direction is away from the side with heat If temperature is decreased in the system, what will happen? equilibrium will shift in the exothermic direction the exothermic direction is towards the side with heat

13

14 H2O H OH

15 H2O H OH H Which way does the see saw have to shift to reach equilibrium again?

16 H2O H OH H Which way does the see saw have to shift to reach equilibrium again?

17 H2O H OH H More H2O is produced due to the shift in equilibrium SHIFT LEFT

18 N2 H2 NH3 N 2 (g) + 3H 2 (g)  2NH 3 (g) H2 NH3

19 N2 H2 NH3 SHIFT will occur to side with the least number of MOLES N 2 (g) + 3H 2 (g)  2NH 3 (g) H2 NH3 SHIFT RIGHT

20 N2 H2 NH3 N 2 (g) + 3H 2 (g)  2NH 3 (g) H2 NH3

21 N2 H2 NH3 SHIFT will occur to side with the least number of MOLES N 2 (g) + 3H 2 (g)  2NH 3 (g) H2 NH3 SHIFT RIGHT

22 Depends if reaction is Endothermic or Exothermic. Endothermic: Heat on LEFT Exothermic: Heat on RIGHT

23 Increase Temperature… which way will the see saw tip? A B D C HEAT

24 Which way will the reaction shift? A B D C HEAT

25 Reaction will SHIFT LEFT A B D C HEAT

26 DecreaseTemperature… which way will the see saw tip? A B D C HEAT

27 Which way will the reaction shift? A B D C HEAT

28 Reaction will SHIFT Right A B D C HEAT

29 Increase Temperature… which way will the see saw tip? A B D C HEAT

30 Which way will the reaction SHIFT? A B D C HEAT

31 Reaction will SHIFT Right A B D C HEAT

32 Decrease Temperature… which way will the see saw tip? A B D C HEAT

33 Which way will the reaction SHIFT? A B D C HEAT

34 Reaction will SHIFT Left A B D C HEAT

35 2NO 2(g)  N 2 O 4(g) + energy (Dark Brown) (Clear)


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