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Equilibrium

Equilibrium. I love chemistry!!!. What is Equilibrium?. A dynamic condition in which 2 opposing changes occur at equal rates in a closed system Ex. A phase change can be a physical condition that can be described to be in equilibrium Solid + ∆H Liquid.

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Equilibrium

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  1. Equilibrium I love chemistry!!!

  2. What is Equilibrium? • A dynamic condition in which 2 opposing changes occur at equal rates in a closed system Ex. A phase change can be a physical condition that can be described to be in equilibrium Solid + ∆H Liquid

  3. Other examples of Equilibrium • Vapor pressure Patm Pgas • Saturated solutions NaCl(s) Na+(aq) + Cl-(aq)

  4. LeChatlier’s Principle • A system will remain at equilibrium until something occurs to change this condition • When a system at equilibrium is disturbed by an application of stress, it attains a new equilibrium position that minimizes that stress

  5. What are the possible stressors? • Change in temperature • Change in pressure • Change in volume • Addition or removal of reactants • Addition or removal of products

  6. Understanding how to minimize the stress • Equilibrium is like a teeter totter • When stress is placed on it, the system must adjust to rebalance itself

  7. Using color to predict shifting ∆H + Co(H2O)6+2(aq) + 4Cl-(aq)CoCl4-2(aq) + 6H2O(l) Pale pink Deep blue At equilibrium, the color of a beaker containing this system would be violet (light purple) What would you see if the following possible stressors were Introduced according to LeChatlier? •Addition of Co(H2O)6+2 •Removal of Cl-(aq) •Removal of H2O(l)•Addition of CoCl4-2(aq) •Addition of ∆H •Removal of ∆H •Increase Pressure •Decrease Pressure

  8. Sample Problem #1 2NO2(g) N2O4(g) + ∆H Very dark brown Very light brown 1. 3. 2. 3. 1. 2. *At equilibrium, the system will display a medium brown color as shown in flask #2

  9. 2NO2(g) N2O4(g) +∆H Very dark brown Very light brown Where would the shifting take place when the following possible stressors are added? What would you see experimentally? • Removal of heat • Increase in pressure • Addition of NO2(g) • Decrease in pressure • Removal of N2O4(g) • Addition of CO2(g) • Addition of heat • Increase in volume of container • Decrease in volume of container

  10. 3. 1. 2. 1. 2. 3. #1 represents a shift to the right (lighter brown color) #2 represents the original equilibrium situation #3 represents a shift to the left (darker brown color)

  11. Things to remember about equilibrium shifting • Pure solids and liquids will not have an effect on equilibrium • Only gases will be affected by a change in pressure or volume

  12. How do you know which side of the equilibrium expression is favored? • Sometimes at equilibrium, there is a higher concentration of reactants or products • To determine this by: • 1. Looking at the equilibrium constant • 2. Looking at the reversible arrows shown in the equation

  13. HBr(aq) + H2O(l) H3O+(aq) + Br-(aq) The forward reaction shown above is favored, therefore there is a higher concentration of products than of reactants at equilibrium H2CO3(aq) + H2O(l) H3O+(aq) + HCO3-(aq) The reverse reaction shown above is favored, therefore there is a higher concentration of reactants than of products at equilibrium

  14. In some cases, both the forward and reverse reactions occur nearly at the same rate before chemical equilibrium is established. Neither reaction is favored • Do not just assume that if you see an equilibrium arrow ( ) that neither side of the system is favored. Use the equilibrium constant to determine for sure!

  15. The equilibrium expression (Keq) • After equilibrium has been achieved, the concentrations of products and reactants remain constant • The ratio of the concentrations should also remain constant ***The only stressor that can affect these concentration ratios is temperature ***Keq is temperature dependant

  16. How do you find Keq? • Keq is the constant that represents the ratio of the mathematical product to the mathematical reactant • The general equation for an equilibrium expression is as follows: nA + mB xC + yD *n, m, x, y = coefficients from balanced chemical equation *A, B, C, D = molarities of reactants and products

  17. nA + mB xC + yD Keq = [C]x [D]y [A]n [B]m *Keq will only change if temperature changes *Only gases and aqueous solution concentrations will be included in Keq *Pure solids and liquids are omitted because their concentrations cannot change

  18. Sample Problem • Consider the following equilibrium equation at 425°C: H2(g) + I2(g) 2HI(g) Write the Keq expression for this reaction Determine Keq mathematically when given the following concentrations: [H2] = .015M, [I2] = .015M, [HI] = .11M Using the known Keq from #2 and given the following concentrations for H2 and I2, determine the concentration of HI: [H2] = .018M, [I2] = .018M

  19. How to use Keq to determine if the reactants, products or neither are favored? • If Keq > 1, the forward reaction (products) are favored • If Keq < 1, the reverse reaction (reactants) are favored • If K = 1, neither reaction is favored (the concentrations of both products and reactants should be equal)

  20. For the previous sample problem, which of the reactions is favored? H2(g) + I2(g) 2HI(g)

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