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Understanding Equilibrium: Reaction Quotient, K, and Shifts in Equilibrium

This lesson focuses on the concept of equilibrium in chemical reactions, specifically how to use the reaction quotient (Q) to predict shifts towards equilibrium. Using the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), students will calculate the equilibrium concentrations of SO2 and O2 based on an initial setup. The lesson explores the effects of changing conditions on equilibrium constants (K) and emphasizes that while K remains constant at a given temperature, equilibrium concentrations can vary. Various examples illustrate how to determine the direction of reaction shifts based on Q values.

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Understanding Equilibrium: Reaction Quotient, K, and Shifts in Equilibrium

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Presentation Transcript

  1. More Equilibrium

  2. Objective/Warm-Up • SWBAT use the reaction quotient (Q) in order to determine how a reaction will shift in order to reach equilibrium. • 2SO2(g) + O2(g) 2SO3(g) • In a certain experiment 2.00 mol of SO2, 1.50 mol of O2 and 3.00 mol of SO3 were placed in a 1.00 L flask. At equilibrium 3.50 mol SO3 were found to be present. Calculate • The equilibrium concentrations of O2 and SO2, K

  3. Playing with K • If we write the reaction in reverse. • lC + mD jA + kB • Then the new equilibrium constant is • K’ = [A]j[B]k = 1/K[C]l[D]m

  4. Playing with K • If we multiply the equation by a constant • njA + nkB nlC + nmD • Then the equilibrium constant is • K’ = [A]nj[B]nk= ([A] j[B]k)n= Kn[C]nl[D]nm ([C]l[D]m)n

  5. K is CONSTANT • At any temperature. • Temperature affects rate. • The equilibrium concentrations don’t have to be the same only K. • Equilibrium position is a set of concentrations at equilibrium. • There are an unlimited number.

  6. Equilibrium and Pressure • Some reactions are gaseous • PV = nRT • P = (n/V)RT • P = CRT • C is a concentration in moles/Liter • C = P/RT

  7. Equilibrium and Pressure • 2SO2(g) + O2(g) 2SO3(g) • Kp = (PSO3)2 (PSO2)2 (PO2) • K = [SO3]2 [SO2]2 [O2]

  8. Equilibrium and Pressure • K =(PSO3/RT)2 (PSO2/RT)2(PO2/RT) • K =(PSO3)2 (1/RT)2 (PSO2)2(PO2) (1/RT)3 • K = Kp (1/RT)2= Kp RT (1/RT)3

  9. Kp =K (RT)(l+m)-(j+k) = K (RT)Dn Dn=(l+m)-(j+k)=Change in moles of gas

  10. What Q tells us • If Q<K • Not enough products • Shift to right • If Q>K • Too many products • Shift to left • If Q=K system is at equilibrium

  11. Example • for the reaction • 2NOCl(g) 2NO(g) + Cl2(g) • K = 1.55 x 10-5 M at 35ºC • In an experiment 0.10 mol NOCl, 0.0010 mol NO(g) and 0.00010 mol Cl2 are mixed in 2.0 L flask. • Which direction will the reaction proceed to reach equilibrium?

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