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Published byElfrieda Gilbert Modified over 9 years ago
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What is equilibrium?What is equilibrium? Chemical reaction stops BEFORE the limiting reactant is consumed. All of the reactants are not COMPLETELY converted to products. o Amount of reactant converting to product = amount of product converting back to reactant Represented in a chemical reaction by arrows pointing in BOTH directions. ( ) Reactant and product concentrations are STABLE
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Ex. H 2 + O 2 H 2 O
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Chemical Reactions at Equilibrium Big Picture/Forest Reaction looks like it is STOPPED. Ex. Helicopter view of traffic jam. Small Scale/Trees Reaction is moving, “dynamic” balance between forward/reverse reactions. Ex. Road view of traffic jam.
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Chemical Reactions at Equilibrium (cont.) Rate of forward = Rate of backward Equilibrium constant expression: o Ratio of the reactant concentration and product concentration. o Concentration MUST be in molarity (M) o A + B C + D o K C = [products] [C][D] [reactants] [A][B]
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Equilibrium Constant (K C )Equilibrium Constant (K C ) constant value for each chemical equation at equilibrium numerical value of ratio The equilibrium constant allows us to …. 1) Predict the direction in which a reaction mixture will proceed to achieve equilibrium. 2) Calculate the concentrations of reactants and products once equilibrium has been reached.
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aA + bB ↔ cC + dD at equilibrium at a given temperature K varies with temperature and is UNITLESS.
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Example (a): Write the equilibrium expression for… PCl 5 (g) PCl 3 (g) + Cl 2 (g) NOTE: [ ] denotes concentration.
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Example (b): Write the equilibrium expression for… 4NH 3 (g) + 5O 2 (g) 4NO (g) + 6H 2 O (g)
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Now you try……Now you try…… 1) 2NO 2 N 2 O 4 2) 2SO 3 2SO 2 + O 2 3) N 2 + 3H 2 2NH 3
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Ex 1: A mixture was found to contain the following concentrations: 0.172 M PCl 3, 0.086 M Cl 2 and 0.028 M PCl 5. Write the equilibrium expression and calculate K. PCl 5 ↔ PCl 3 + Cl 2
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How do we use a value like k=0.53 to determine a reaction’s direction??? When k >> 1, PRODUCTS are favored. When k << 1, REACTANTS are favored. Think about this statement using ………… o K C = [products] [reactants]
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Equilibrium Worksheet
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