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Reaction Rates and Equilibrium

Reaction Rates and Equilibrium. Rate and Collisions. Reaction rate = amount of reactant changing over time Collision Theory—atoms, ions, or molecules can form new products when they collide with enough kinetic energy. Factors Affecting Rate. Temperature—usually, raising temp. speeds up a rxn.

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Reaction Rates and Equilibrium

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  1. Reaction Rates and Equilibrium

  2. Rate and Collisions • Reaction rate = amount of reactant changing over time • Collision Theory—atoms, ions, or molecules can form new products when they collide with enough kinetic energy

  3. Factors Affecting Rate • Temperature—usually, raising temp. speeds up a rxn. • Concentration—greater conc. speeds up a rxn. • 2HCl + Mg → MgCl2 + H2

  4. Factors Affecting Rate • Particle size—increased surface area speeds up a rxn. • CH3CH2OH + 3O2→ 2CO2 + 3H2O • Catalysts—lowers activation energy with its presence • 3CuSO4 + 2Al → Al2(SO4)3 + 3Cu

  5. Activation energy • Activation energy—minimum amt. of energy particles must have in order to react. • This is a “hump” that the reactants need to get over in order to form new compounds. • At the peak of the hump, the particles form an “activated complex” or “transition state” that lasts for an instant. • (see video hldxchng) Shortcut to HLDXCHNG

  6. Reversible Rxns. • Some rxns can proceed in either direction: • 2SO2(g) + O2(g)→ 2SO3(g) Or • 2SO3(g) → 2SO2(g) + O2(g)

  7. Equilibrium • When the rate of the forward rxn and the rate of the reverse rxn are the same, the rxn has reached chemical equilibrium. • This DOES NOT mean that the concentration of products and reactants is the same. • At equilibrium, no change in the amount of rxn components occurs.

  8. 2C2H6(g) + 7O2(g)→ 4CO2(g) + 6H2O(g) • Keq = • If Keq = 0.13, does equilibrium lie to the right or the left? • If Keq = 3.58, does equilibrium lie to the right or the left? • Why would the value of Keq change?

  9. LeChatelier’s Principle • If a stress is applied to an equilibrium system, the system will respond to relieve the stress.

  10. Upsetting Equilibrium • Concentration—system will adjust to minimize the effect of added reactant/product. • If a reactant/product is removed, system will respond to fill that void. 2CrO4 + 2H3O+↔ Cr2O7 + 3H2O

  11. Upsetting Equilibrium • Temperature—increasing temp. causes system to shift in the direction that absorbs heat. Cooling the system pushes it in the direction of producing heat. • 2SO2(g) + O2(g)→ 2SO3 + heat

  12. Upsetting Equilibrium • Pressure—this only affects gases. With additional pressure, the rxn shifts to the side with fewer particles. • N2(g) + 3H2(g)→ 2NH3(g)

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