Chapter 13 Chemical Equilibrium

Reversible Reactions ___________ react to form products. _________ then react to form reactants. _____ reactions occur: ________ aA + bB  cC + dD _______

CONCENTRATIONS __________ CHANGE! EQUILIBRIUM OCCURS When the amount of __________ becoming __________________ the amount of _________ becoming __________. CONCENTRATIONS __________ CHANGE! When the _________ and _________ reactions rates are ______.

EXAMPLE 2HI(g) ↔ H2(g) + I2(g) 2 HI react to form H2 and I2 As H2 and I2 build up, they react to form HI

EQUILIBRIUM EXPRESSION If we compare the concentrations of all the reactants and products at equilibrium, we discover a relationship: k = [ ]p [ ]r Can be many equilibrium concentrations possible for a given temp, ______________ Includes only _______ and ________, no pure solids or liquids K and Keq and Kc can be substituted for each other.

2HI(g) ↔ H2(g) + I2(g) Write the equilibrium expression for this reaction.

N2(g) + H2(g)  NH3(g) Write the equation and the equilibrium expression for the synthesis reaction between N2(g) and H2(g) to form NH3(g) NOW….Write the equation and the equilibrium expression for the decomposition of NH 3(g) WHAT DO YOU NOTICE ? Inverse of each other

ANOTHER REACTION Write the equation and the equilibrium expression for N2O4(g) decomposing into NO2 (g) NOW write the equation and the equilibrium expression for 1/2N2O4 forming NO2(g) WHAT DO YOU NOTICE ?

General rules K = [products]p [reactants]r If you reverse the reaction, you _____the K If you double the reaction, you _____the K If you halve the reaction, you _____ the K

TRY THIS ONE ! Given this equilibrium expression: K = [SO2]2[O2] Write the balanced equation.

Equilibrium Calculations If you know the equilibrium concentrations of reactants & products, you can solve for K. aA + bB  cC + dD K = [C]c[D]d [A]a[B]b

Sample Problem When solid ammonium chloride is heated, it reaches equilibrium with ammonia and hydrogen chloride. It is found that at equilibrium at 500oC in a 5.0 L container, there is 2.0 mol NH3, 2.0 mole HCl, and 1.0 mol NH4Cl. Calculate K for this system.

GASES Equilibrium problems can be done using the partial pressures of gases, and solving for Kp Parenthesis are substituted for brackets. See Example 13.4 in text

Kp and Kc A relationship exists between Kc and Kp. Kp= K(RT)Δn R = .08206 L atm/mol K T = temp in K Dn = sum of the coefficients of the gas product minus sum of the coefficients of the gas reactants Example 13.5

Homogeneous Equilibria all reactant and products are in the ________ Heterogeneous Equilibria Check out 13.6 later!

K allow us to predict several things about the reaction: 3)

Tendency of a Reaction to Occur If K>1, mostly _________ exist, equilibrium lies far to the ______ _________ Rxn is predominant 2. If K<1, mostly ________, equilibrium lies far to the _____

Reaction Quotient Given some reactants AND some products together in a reaction vessel, which reaction ( or ) will occur to reach equilibrium. Compare Q to K K uses ____________ concentrations Q uses ___________ concentrations

Q and K Sample Exercise 13.7 If K < Q, reaction shifts _______ If K = Q, reaction is __________

Calculate Equilibrium Concentrations If given K & original concentrations, you can find equilibrium concentrations using an ICE chart

THE ICE CHART Reactant and Products are listed here! Time for lots of examples and practice! Reactant and Products are listed here! I write my ICE chart underneath the balanced equation. Initial Change Equilibrium

Le Chatelier’s Principle When a chemical system is at equilibrium, and something changes- that change is a “_________”. The equilibrium will adjust __________ _________________ It will move ________ or ________ to reduce the stress. Common stresses are changing ________ _______________________________

Concentration ________ reactant or product, equilibrium _________________ the addition. __________ reactant or product, equilibrium ___________ the subtraction Try 13.13

Pressure Can be changed by 1) 2) 3) Volume change directly related to moles _______ volume, shift to ______ # of moles Try 13.14

Temperature Treat changes in temp ______________ _______________________ Treat heat like any other ________ or ___________. Must know if rxn is ____________ or ___________ _________ heat, shift ________ the heat __________ heat, shift _______the heat Try 13.15

NOW WE PRACTICE A LOT!!!!