CHEMISTRY: Reaction Rates & Chemical Equilibrium

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Collision Theory
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reaction takes place only when the molecules collide with proper orientation and sufficient energy
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Activation energy
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minimum amount of energy needed to break the bonds b/w atoms of reactants; min energy for reaction to occur
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What are the 3 conditions required for a reaction to occur?
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Collision of reactants, proper Orientation, and Sufficient energy
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How is the rate of a reaction determined?
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by measuring the amount of a reactant used up, or the amount of product formed in a certain amount of time
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Reaction Rate
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Reaction rate=∆ concentration of reactant/product÷∆ time
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Factors that affect rate of reaction are?
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Temperature, concentration, and addition of catalyst
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How does temp affect reaction rate?
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@ ↑ temp the ↑ in kinetic energy makes reacting molecules move faster, causing more collisions, and sufficient energy to react
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How does concentration affect rate of reaction?
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the rate of reaction ↑ with the ↑ in concentration of reactants
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How does a catalyst affect the rat of reaction?
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catalyst speeds up reactions in both directions equally by decreasing activation energy; doesn’t participate in reaction
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Reversible reactions
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*proceed in both forward and reverse directions *2 reaction rates (forward & reverse) *molecules react, forward reaction is faster than reverse *products accumulate, forward reaction decreases, reverse increases
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Chemical Equilibrium
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when there are no further changes in the concentration of reactants or products
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What happens at chemical equilibrium?
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reactions occur in opposite direction @ the same rate, which means concentration of the reactants/products remain constant
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Explain equilibrium constant expression.
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*multiply the concentration of products *divide by concentration of reactants *raised to a power (the coefficient in the balanced equation) *bracket around each substance (to rep mol/L or M)
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Define equilibrium constant (Kc).
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numerical value obtained by substituting molar concentrations @ equilibrium into expression: Kc=[Product]÷[Reactant]
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A reaction in which all the reactants & products are gases
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Homogeneous Equilibrium
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When reactants are in 2 or more states
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Heterogeneous Equilibrium
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Are liquids and solids included in equilibrium constant? Why/Why not?
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concentration of pure solids & liquids in heterogeneous equilibrium are constant; therefore NOT included in equilibrium constant
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A reaction at specific heat has how many values for Kc?
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1; one
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Which are reversible? a. breaking glass b. melting snow c. heating a pan
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b. melting snow
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Which are at equilibrium? a. the rate of forward reaction is 2× faster than rate of reverse b. concentration of reactants/products doesn’t change c. rate of reverse reaction doesn’t change
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b. concentration of reactants/products doesn’t change c. rate of reverse reaction doesn’t change
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Which is the correct Kc expression for the reaction. CH₄(g)+2H₂S(g)⇌CS₂(g)+4H₂(g) a. Kc=[CS₂][H₂]⁴÷[CH₄][H₂S]² b. Kc=[CS₂][H₂S]⁴÷[CH]⁴[H]₂⁴
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a. Kc=[CS₂][H₂]⁴÷[CH₄][H₂S]²
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Size of equilibrium constant depends on what?
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whether equilibrium is reached with more reactants than products or vice versa
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What effect does the size of Kc have on rate of equilibrium?
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none, size of Kc doesn’t effect how fast equilibrium is reached
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Large Kc
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large amount of product
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Small Kc
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large amount of reactants; very small Kc produces almost no products
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Kc close to 1 (rare)
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equal concentration of reactants & products
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Le Châtelier’s Principle
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a system that is disturbed at equilibrium will shift in the direction that will reduce the stress to reestablish equilibrium
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Concentration change, how does reaction shift? a. add reactant b. add product c. remove reactant d. remove product
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a. reaction shifts→products (more products) b. reaction shifts→reactants (more reactants) c. reaction shifts→reactants d. reaction shifts→products
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If the volume of a gas mixture changes at equilibrium, what must also change?
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Concentration of the gases
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An increase/decrease in volume of gases will affect concentration, how?
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↑ volume ↓concentration; ↓volume ↑concentration
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On which side of the equation is heat written in endothermic and exothermic reactions?
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Endothermic ; right (reactant side) Exothermic ; left (product side)
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How does temperature affect endothermic reactions?
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↑heat; reaction shifts →products (to remove heat) ↓heat; reaction shifts →reactants (to add heat)
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How does temperature affect exothermic reactions?
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↑heat; reaction shifts→reactants (to remove heat) ↓heat; reaction shifts→products (to add heat)
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Indicate whether the Kc has mostly products, reactants, or both: a. Kc=3.7×10⁸ b. Kc=4.7 c. 1.7×10⁻⁵⁶
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a. mostly reactants b. both c.mostly products
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Indicate how the system shifts for each change for the given reaction: 3O₂(g)+heat⇌2O₃ a. add more O₂ b. add more O₃ c. increase temp d. increase volume of container e. add catalyst
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a. reaction shifts→product (remove heat) b. reaction shifts→reactant (add heat) c. reaction shifts→product (increase rate) d. reaction shifts→reactant (more moles) e. reaction shifts→increases rate of both reactions equally

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