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Keq vs. Q

Keq vs. Q. Angelica Miranda, Marcus Moss, Jaymi Gooden. When Do You Use This?. To determine if a reaction is at equilibrium at given time and temperature. Need-To-Know Definitions. Equilibrium: A chemical reaction and its reverse proceeds at equal rates. K: The equilibrium constant

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Keq vs. Q

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  1. Keq vs. Q Angelica Miranda, Marcus Moss, Jaymi Gooden

  2. When Do You Use This? • To determine if a reaction is at equilibrium at given time and temperature.

  3. Need-To-Know Definitions • Equilibrium: A chemical reaction and its reverse proceeds at equal rates. • K: The equilibrium constant • Q: A mathematical statement that is determined while the reaction is occuring

  4. Steps and Rules • Chateliers' Principle: describes what happens to a system when something momentarily takes it away from equilibrium. • It focuses on three ways in which we can change the conditions of a chemical reaction at equilibrium: (1) changing the concentration of one of the components of the reaction (2) changing the pressure on the system (3) changing the temperature at which the reaction is run. (continued)

  5. Write equilibrium expression using the given products and reactants in the chemical equation. • Plug in the given concentrations of each molecule into the equation • Solve for Q • Compare Q to Keq and determine if the concentration shifts to the left or right or if has reached equilibrium.

  6. Example Problem • Problem #1When 0.40 moles of PCl5 is heated in a 10.0 L container, an equilibrium is established is which 0.25 moles of Cl2 is present. PCl5(g) <====> PCl3(g) + Cl2(g) a) What is the number of moles of PCl5 and PCl3 at equilibrium?b) What are the equilibrium concentration of all three components?PCl5 <=====> PCl3 + Cl2start 0.40 moles ------ -------after 0.15 moles 0.25 moles 0.25 moles From the balanced equation and the coefficients it should be obvious that everything works on a one-to-one basis. So there should be 0.25 moles of PCl3 and 0.25 moles of PCl5 should have been consumed, so there are 0.40-0.25 moles = 0.15 moles of PCl5 left.Therefore [PCl5] = 0.15 moles = 0.015 moles/L10.0 L[PCl3] and [Cl2] both are 0.25 moles each. Therefore their concentrations are identical as well.[PCl3] = [Cl2] = 0.25 moles = 0.025 moles/L10.0 L

  7. Practice Problem 2N2O + O24NO Write the equilibrium expression Answer: Keq= [NO]4 --------------- [N20]2[O2]

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