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EQUILIBRIUM BASICS

EQUILIBRIUM BASICS. Chapter 14.1-14.3. Lesson Objectives. Which of the following is NOT true about a reaction at equilibrium? N 2 O 4  2NO 2. [N 2 O 4 ] = 2 [NO 2 ] The rate of the forward and reverse reactions are the same

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EQUILIBRIUM BASICS

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  1. EQUILIBRIUM BASICS Chapter 14.1-14.3

  2. Lesson Objectives

  3. Which of the following is NOT true about a reaction at equilibrium?N2O4 2NO2 • [N2O4] = 2 [NO2] • The rate of the forward and reverse reactions are the same • The equilibrium constant will describe whether the process favors reactants or products • [N2O4] and [NO2] remain constant. • For every 2 molecules of NO2 reacted, 1 molecule of N2O4 is produced

  4. AT EQUILIBRIUM • Two reactions are occurring (forward and reverse) indicated by double arrow. • Equilibrium definition: a reaction has reached equilibrium (balance) when the forward and reverse reactions occur at the same RATE. • This means that concentrations of reactants and products stay CONSTANT over time

  5. An Equilibrium Example See this interactive tutorial here

  6. Equilibrium factors: • Equilibrium IS dependent on • TEMPERATURE (affects the equilibrium constant, K) • It is NOT dependent on • Original concentrations • Volume of the container • Total pressure of the system • Remember – the partial pressure of a gas in a mixture is proportional to the mole fraction of that gas in the mixture!

  7. The following data are for the system A(g) 2B(g) How long does it take the system to reach equilibrium?

  8. K: equilibrium constant • Tells us the extent to which the reaction will go until it reaches equilibrium • Large K means the reaction goes mostly to product • Small K means the reaction stays mostly as reactant

  9. For a reaction2A(g) + B(g)  2C(g) K = 1 x 1083which of the following can be concluded? • At equilibrium, [A] = ½[B] = [C] • At equilibrium, the largest concentration is [A] • At equilibrium, the largest concentration is [C] • This reaction favors the reactants • This reaction happens very quickly

  10. Writing K expression (equilibrium expression) • Uses only gaseous or aqueous products and reactants (no solids or liquids; their concentrations do not change during reactions) • Coefficients become exponents • Products over reactants • For aA + bBcC + dD Kp = or Kc= • Relate to each other: Kp = Kc(RT)Δng • R = gas law constant (0.0821 atm·L/mol·K) • Δng = change in moles of gas (products – reactants) (PC)c x (PD)d [C]c [D]d [A]a [B]b (PA)a x (PB)b

  11. Which of the following species should NOT be included in the equilibrium constant expression for the reaction?2A(s) + B(aq)  2C(l) + D(g) • A, B, C • B, C • A, C • A, C, D • B, D

  12. For a reaction 2A + B  2CWhen equilibrium is established, the ratio of products to reactants (K) = 0.5. Which of the following initial conditions could be changed to cause a different equilibrium constant value? • Start with more A • Dilute the reaction by adding water • Increase the temperature of the reaction • Add a catalyst

  13. To calculate Kp from Kc for the reactionA(g) + 2B(g)  C(g)what would be the exponent to which Kc(RT) is raised? • -2 • -1 • 0 • 1 • 2

  14. Write the equilibrium constant (K) expressions for the following reactions: I2(g) + 5F2(g)2 IF5(g) SnO2(s) + 2H2(g)Sn(s) + 2H2O(l)

  15. For the reaction2 NO(g) + O2(g)  2 NO2(g)determine the Kp at 298K if Kc is 4.67 x 1013

  16. True or False? • Given the equation below, N2 + 3H2 2 NH3 if one mole of N2 is mixed with 3 moles of H2, 2 moles of NH3 will form.

  17. True or False? • Given the equation below, N2 + 3H2 2 NH3 for every 1 mole of N2 that reacts, 3 moles of H2 will also react and 2 moles of NH3 will form.

  18. Calculate K for the reactionNH4CO2NH2(s)  2 NH3(g) + CO2(g) if at equilibrium there are 0.159 g of NH4CO2NH2 and pressures of 0.0451 atm of CO2 and 0.0961 atm NH3

  19. K depends on the form (coefficients) of the balanced equation! • This means that K changes when: • The coefficients are multiplied • Reactions are reversed • Reactions are added together (mechanism)

  20. Coefficient rule: • If coefficients are multiplied by a factor (n), then K is RAISED TO THE (n) EXPONENT • A2 (g) + 2B (g) 2AB (g) K = • 3A2 (g) + 6B (g) 6AB (g) K = PAB2 PA x PB2 PAB6 PA3 x PB6

  21. Calculate K for the formation of 2 moles of ICl(g)ICl (g) ½I2 (g) + ½Cl2 (g) K = 2.2x10-3

  22. Reciprocal rule: • If the reaction is reversed, K of the forward and K of the reverse are reciprocals of each other (new K = 1/old K) • A2 (g) + 2B (g) 2AB (g) K = • 2AB (g) A2 (g) + 2B (g) K = PAB2 PA x PB2 PA x PB2 PAB2

  23. Rule of multiple equilibria • If multiple reactions are added together to get an overall reaction, the overall K is the PRODUCT of the individual K’s A2 (g) + 2B (g) 2AB (g) 2AB (g) + C (g) A2B2C (g) A2 (g) + 2B (g) + C (g) A2B2C (g) Find overall K it by multiplying individual K’s:

  24. Given the reactions below and their constants, calculate K for the rxn:Fe(s) + H2O(g) FeO(s) + H2(g) H2O(g) + CO(g) H2(g) + CO2(g) K = 1.6 FeO(s) + CO(g) Fe(s) + CO2(g) K = 0.67

  25. Determining K • K must use values AT EQUILIBRIUM! • When given initial concentrations or pressures in a problem , you must determine what the values will be at equilibrium before you can calculate K • Use an ICE Chart to determine how the initial values will increase or decrease to get to equilibrium, then solve for K. • Solids and liquids have no effect on equilibrium, so they don’t need values in your ICE chart.

  26. The ICE Chart • Initial/Change/Equilibrium • Given initial pressures, find equilibrium constant A2= 0.1 atm B = 0.2 atm A2(g) + 2B(g)  2AB(g) I C E 0.0 atm 0.2 atm 0.1 atm +2x -x -2x 0.1 - x 2x 0.2 - 2x

  27. For the decomposition reactionNH4HS(s)  NH3(g) + H2S(g) • In a sealed flask are 10.0 g of NH4HS, NH3with a partial pressure of 0.692 atm and H2S with a partial pressure of 0.0532 atm. When equilibrium is established, it is found that the partial pressure of NH3 has increased by 12.4%. Calculate K for this reaction.

  28. Lesson Objectives

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