Chapter 19 – Reaction Rates and Equilibrium
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Transcript of Chapter 19 – Reaction Rates and Equilibrium
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Chapter 19 – Reaction Rates and Equilibrium
Rates of ReactionReversible Reactions and EquilibriumDetermining Whether a Reaction Will OccurCalculating Entropy and Free EnergyThe Progress of Chemical Reactions
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19.1 Rates of Reaction
How long does a chemical reaction take?
Collision Theory IF colliding particles
have enough energy (KE) and collide at the right orientation, they react to form a new product:
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19.1 Rates of Reaction (cont.)
The minimum amount of energy that particles must have in order to react is called the activation energy.
Activation energy acts like a barrier that the reactants must cross to be converted into products.
Activated complex, transition state…
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19.1 Rates of Reaction (cont.)
Factors Affecting Reaction Rates Here they are
again… Temperature Concentration Particle size Catalysts
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19.2 Reversible Reactions and Equilibrium
Reversible Reactions Reactions that can occur in the other direction.. 2SO2 + O2 2SO3
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19.2 Reversible Reactions and Equilibrium (cont.)
Chemical Equilibrium A state in which the forward and reversible reactions
take place at the same rate.
Factors Affecting Equilibrium: Le Chatelier’s Principle Obviously, when discussing equilibrium there is “a fine
line” of balance in the reaction – changes of almost any kind can disrupt this balance.
Le Chatelier’s Principle: If a stress (temp, conc., pressure) is applied to a system in dynamic equilibrium, the system changes to relieve the stress.
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19.2 Reversible Reactions and Equilibrium (cont.)
Equilibrium Constants A ratio of product concentrations… aA + bB cC + dD
Keq = [C]c x [D]d / [A]a x [B]b
where [X] is expressed in mol/L and x is the number of moles from the balanced chemical equation.
A Keq value > 1 favors products at eq.
Keq value < 1 favors reactants at eq.
Examples…
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Ch 19 Assignments
Ch 19 CPQs #1 pg. 572 #38,39,40,41,43,44,46,47,48,49,50
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19.3 Determining Whether a Reaction Will Occur
Free Energy and Spontaneous Reaction To do work, you need available energy. Free energy: energy that is available to do work. (Not
always efficient. Reactions may OR may not occur spontaneously…
Entropy Reactions tend to occur to attain the lowest possible
energy for a system: the law of disorder. The disorder in a system is measured as entropy, (S).
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19.3 Determining Whether a Reaction Will Occur (cont.)
Entropy explained and visualized…
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19.3 Determining Whether a Reaction Will Occur (cont.)
Entropy explained and visualized…
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19.3 Determining Whether a Reaction Will Occur (cont.)
Entropy explained and visualized…
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19.3 Determining Whether a Reaction Will Occur (cont.)
Entropy explained and visualized…
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19.3 Determining Whether a Reaction Will Occur (cont.)
Heat, Entropy, and Free EnergyThe size and direction of heat
(enthalpy) changes combined with entropy determine whether or not a reaction is spontaneous, i.e., whether it favors products and releases free energy.
Table 19.1, pg. 554
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19.3 Determining Whether a Reaction Will Occur (cont.)
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19.4 Calculating Entropy and Free Energy
Entropy Calculations Standard entropy change (entropy change at standard
conditions: So = So (products) – So (reactants) Use Table 19.2 Examples…
Free Energy Calculations The maximum amount of energy that can be combined with
another process to do work: Gibbs Free-Energy (G). G = H – TS where H = enthalpy, T = Temperature Go = Go
f (products) – Gof (reactants)
Tables 19.3 and 19.4 Examples…
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19.5 The Progress of Chemical Reactions
Rate Laws Fortunately, we don’t have to settle for explanations that
are qualitative in nature- in other words, “the reaction will likely favor the products…”
Mathematically calculating rates of reaction… Rate Law: an expression relating the rate of a reaction
to the concentration of reactants: Rate = A / t = k x [A]
For the reaction aA + bB cC + dD, the rate equation takes the form:
Rate = k[A]a[B]b
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19.5 The Progress of Chemical Reactions (cont.)
Rate Laws (cont.) The specific rate constant,k, determines the relationship
between the concentrations and the rate of reaction. If k is large, the reaction will form products quickly. If k is small, the reaction will form products slowly. The order of a reaction is the power to which the
concentration must be raised to give the experimentally observed relationship between concentration and rate: 1st order reaction – proportional to one reactant.
Reaction mechanisms… Showing the reactions involved in a complex reaction Figure 19.3, decomposition of N2O…
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Ch 19 Assignments
Ch 19 CPQs #1 pg. 572 #38,39,40,41,43,44,46,47,48,49,50
Ch 19 CPQs #2 pg. 572 #51,53,54,55,56,59,61,62