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Review for energetics and kinetetics test

Review for energetics and kinetetics test. Energy and reaction rates. Energy. Energy = ability to do work. Law of conservation of energy = first law of thermodynamics. Chemical potential energy = stored energy in bonds. 1 calorie = 4.184 joules = 1/1000 Calories

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Review for energetics and kinetetics test

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  1. Review for energetics and kinetetics test Energy and reaction rates

  2. Energy • Energy = ability to do work. • Law of conservation of energy = first law of thermodynamics. • Chemical potential energy = stored energy in bonds. • 1 calorie = 4.184 joules = 1/1000 Calories • Specific heat = heat to raise 1 gram 1° C.

  3. Energy • Heat = specific heat x mass x change in temperature • q = c x m x ΔT • A calorimeter is an insulated device used to find specific heats. • Page 524 gives an example of this in use • Be able to use this equation to solve for any unknown.

  4. Energy • Thermochemistry is the study of heat changes that go with reactions and phase changes. • System = specific area of reaction • Surroundings = everything else • Universe = system + surroundings • Enthalpy is heat content of a system at constant pressure.

  5. Energy • Change in heat of a reaction is the change in enthalpy = ΔH. • ΔH = Hproducts – Hreactants • Exothermic = -ΔH • Endothermic = +ΔH

  6. Energy • A thermochemical equation is a balanced chemical equation with the physical states of all the reactants and products, and energy change. • Enthalpy of combustion (ΔHcomb) is the enthalpy change of the complete burning of one mole of a substance.

  7. Energy • Molar enthalpy (heat) of vaporization (ΔHvap) is the heat to vaporize one mole of liquid. • Molar enthalpy (heat) of fusion (ΔHfus) is the heat needed to melt one mole of a solid. • ΔHvap = -ΔHcond • ΔHfus = ΔHsolid

  8. Energy • Hess’s Law is a way to take intermediate steps to find the overall energy change for a reaction. • Standard enthalpy (heat) of formation (ΔH°f) is the energy needed to form one mole of substance in standard state from the elements in standard state. • ΔH°rxn= ΣΔH°f (products) - ΣΔH°f(reactants)

  9. Energy • Entropy is the number of ways a systems energy can be distributed (directly related to freedom of particles). • Second law of thermodynamics states that spontaneous process happen in a way that increases the entropy of the universe. • Change in entropy (ΔS) is equal to products – reactants.

  10. Energy • You can predict ΔS by examining the process. • Change in state can be predicted by change in movement. • Gas dissolved into solvent lowers movement. • More gas = more entropy. • Solid or liquid into solvent increases entropy. • Entropy increases with temperature increase.

  11. Energy • Gibbs free energy equation lets you know how much energy is available to do work. • ΔGsystem = ΔHsystem – TΔSsystem • This is used to tell reaction spontaneity. (– values are spontaneous, + are nonspontaneous) A list of situations is on page 547.

  12. Reaction rates • Reaction rate is a change in concentration in a given time, usually in mol/(L s). • Represented by brackets around a substance. [NO] is molar concentration of NO. • Reaction rate = ΔM/Δt

  13. Reaction rates • Collision theory relates collisions with reaction speed. • Collisions need to be orientated correctly and have enough energy. • When collisions are correct, an activated complex is formed for a brief time. • Activation energy (Ea) is the amount of energy needed to for the activation complex.

  14. Reaction rates • Factors affecting reaction rate: • Nature of reactants. (some are more reactive) • Higher concentrations react more readily • More surface are allows more collisions • Higher temperature allows more collisions with more energy • Catalysts increase speed (lower activation energy) inhibitors slow speed.

  15. Reaction rates • Rate laws show the relationship between concentration and speed/rate. • General rate law is: • rate = k[A]m [B]n • k = rate constant • m and n are reaction orders • Method of initial rates determines the reaction rate through experimental results of various concentrations. (page 576)

  16. Reaction rates • Instantaneous reaction rates are the slope of the straight line tangent to the curve at the given instant. • This can also be found with concentrations, temperature, rate law and rate law constant at that temperature.

  17. Reaction rates • A reaction mechanism is the complete sequence of steps of a reaction. • Complex reactions have more than one elementary step. • Intermediates are formed in one elementary step and consumed in another. • The rate determining step is the slowest step that holds everything else up.

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