Chemical Equilibrium

Transcription

1 Chemical Equilibrium

2 Forward Rxn: A + B C + D Reverse Rxn: A + B C + D Written as: A + B C + D OR A + B C + D

3 A reversible reaction has both an endothermic rxn and an exothermic rxn Reactants Exothermic (high to low E) (release) Products Endothermic (low to high E) (absorb)

4 At As first the when reactants a reaction are used begins, up, the rate reactants of begin the forward forming reaction productsslows down

5 When there are more products, the reverse happen reaction at the rate same begins time to increase The forward and reverse reactions

6 When The If a system rate the forward rate is in forward Chem = the EQ rate = then back rate the as back long you as the factors concentrations have chemical that control equilibrium must rates be constant stay the same 7 reactant particles 3 product particles

7 State of balance When [reactants] and [products] are constant

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9 when a system at equilibrium is disturbed by a change in temp., pressure, or conc., the system shifts its equilibrium to counteract this change. new equilibrium old equilibrium C D A B added to system

10 Concentration Adding or removing a reactant or product Temperature Heating or cooling a reaction Dependent on if reaction is endo or exo Pressure Only affects reactions with gases A shift is when a stress is applied to a reaction and the system corrects the change

11 If concentration of a substance increases, then the reaction shifts away from the increase If concentration of a substance decreases, then the reaction shifts towards the decrease

12 N 2 + 3H 2 2NH 3 The reaction is at equilibrium Change: H 2 is added to the system More NH 3 needs to be made to use up the H 2 and return the system back to equilibrium So the system will go towards products by: Shifting RIGHT

13 N 2 + 3H 2 2NH 3 The reaction is at equilibrium Change: NH 3 is added to the system More N 2 and H 2 need to be made to use up the NH 3 and return the system back to equilibrium So system will go towards reactants by: Shifting LEFT

14 Endothermic: A + B + energy C + D If temp increases, then the reaction shifts away from the increase, towards products If temp decreases, then the reaction shifts towards the decrease, towards reactants Exothermic: A + B C + D + energy If temp increases, towards reactants If temp decreases, towards products

15 N 2 + 3H 2 2NH kJ The reaction is at equilibrium Change: system is cooled Removing heat from the system So the system will go towards products by: Shifting RIGHT

16 N 2 + 3H 2 2NH kJ The reaction is at equilibrium Change: system is heated Adding heat to the system So the system will go towards reactants by: Shifting LEFT

17 Only affects gases because affects volume of system Need to count # of moles of gases (coefficients) Increase in pressure means decrease in volume, so the reaction will shift to the side with fewer moles of gas Decrease in pressure means an increase in volume, so the reaction will shift to the side with more moles of gas

18 N 2 (g) + 3H 2 (g) 2NH 3 (g) The reaction is at equilibrium Change: pressure is decreased = 4 moles of gas on the left 2 moles of gas on the right So the system will go towards reactants by: Shifting LEFT

19 Predict how each of the following will affect the equilibrium: H 2 (g) + CO 2 (g) H 2 O (g) + CO (g) Adding H 2 O to the system Removing CO from the system Adding H 2 to the system Adding a catalyst Nothing b/c only affects speed not reaction Increase the volume of the system Nothing b/c equal # of moles