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Factors Affecting Reaction Rates

Factors Affecting Reaction Rates. Factors Affecting Reaction Rates. There are several factors affect reaction rates Concentration Surface area (Particle size) Temperature Catalysts Inhibitors. Catalysts.

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Factors Affecting Reaction Rates

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  1. Factors Affecting Reaction Rates

  2. Factors Affecting Reaction Rates • There are several factors affect reaction rates • Concentration • Surface area (Particle size) • Temperature • Catalysts • Inhibitors

  3. Catalysts • A catalyst is a substance that increases the rate of a chemical reaction without itself being used up in the reaction. • A catalysts provide an alternative energy pathway for the reaction. • The different pathway lowers the activation energy allowing more molecules to overcome the activation energy and produce products at a faster rate

  4. Potential Energy H A lower activation energy allows more molecules to overcome the activation energy, speeding up the reaction

  5. Inhibitor • An inhibitor is a substance that slows down, or inhibits reaction rates. • Uses • A preservative • A weed killer

  6. Equilibrium : A State of Dynamic Balance

  7. Reversible Reactions • When a reaction results in complete conversion of reactants to products chemists say it goes to completion • Not all reactions go to completion. They appear to stop because they are reversible • Reversible reactions can occur in both the forward and reverse directions

  8. Reversible Reactions cont. . . • Forward N2 + 3H2 2NH3 • The product is NH3 • Reverse N2 + 3H2  2NH3 • The product is N2 and H2 N2 + 3H2⇆ 2NH3 The forward and reverse reactions are happening at the same time.

  9. Question Time • What do chemists say when all the reactants are completely converted to products? • In all reactions are all the reactants converted to products? • What is a reversible reaction?

  10. Chemical Equilibrium • Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates. • Rateforward reaction = Ratereverse reaction • This does notmean the concentrations of the products and reactants are the same • Equilibrium is a state of action, not inaction. This process is dynamic; dynamic equilibrium.

  11. http://www.youtube.com/watch?v=JsoawKguU6A

  12. Question Time • What is chemical equilibrium? • Are the rates of the forward and reverse reaction at equilibrium the same or different? • Are the concentrations of the products and reactants always the same at equilibrium?

  13. Equilibrium Expression and Constant (Keq) • Law of chemical equilibrium states that at a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value known as Keq or equilibrium constant.

  14. Equilibrium Constant Keq • Keq is the ratio of product concentrations to reactant concentrations. • Keq only includes compounds that are in the gaseous or aqueous state, not solid or liquid • A large Keq, Keq > 1 means the products are favored over the reactants • A small Keq, Keq < 1 means the reactants are favored over the products

  15. Homogenous vs. Heterogeneous Equilibrium • Homogenous equilibrium means all reactants and products are in the same physical state • Ex: H2(g) + O2(g)  H20(g) • Heterogeneous equilibrium is when the reactants and products are in more than one physical state. • Ex: H2O(g) + C(s)  H2(g) + CO(g)

  16. Question Time • What is the Law of Chemical Equilibrium? • What does Keq stand for? • What is Keq? • What does it mean to have a large Keq? • What does it meant too have a small Keq? • What is homogenous equilibrium? • What is heterogeneous equilibrium?

  17. Chemical Equilibrium—Keq aA + bB  cC +dD products [C]c [D]d reactants [A]a [B]b Keq = = **only use Keq for gasses and aqueous compounds

  18. Homogenous Equilibria • Given N2(g) + 3H2(g) 2NH3(g) write the equilibrium constant expression for the reaction.

  19. Given SO2(g) + O2(g) 2SO3(g) write the equilibrium constant expression for the reaction.

  20. Heterogeneous Equilibria • Given 2NaHCO3(s) Na2CO3(s) + CO2(g) +3H2O(g) write the equilibrium constant expression for the reaction.

  21. Calculating the Value of Equilibrium Constants At equilibrium and 100°C a flask contains: [PCl5]=0.0325M [H2O]=0.025M [HCl]=0.375M [POCl3]=0.250M Calculate the Keq for the reaction PCl5(g) + H20(g) 2HCl(g) + POCl3(g)

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