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Chemical Change: Energy, Rate and Equilibrium Thermodynamics: study of energy, work and heat

Explore the principles of chemical reactions including types of energy involved, exothermic and endothermic reactions, laws of thermodynamics, kinetics, factors influencing reaction rates, chemical equilibrium, and Le Chatelier's Principle.

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Chemical Change: Energy, Rate and Equilibrium Thermodynamics: study of energy, work and heat

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  1. Chemical Change: Energy, Rate and Equilibrium Thermodynamics: study of energy, work and heat Kinetic energy: energy of motion Potential energy: energy of position, stored energy Chemical reactions involve changes in energy. Types of energy include: Heat, sound, electricity, light, motion, etc. Example: 2H + O2 2H2O + energy

  2. Exothermic Reaction: Reaction that releases heat to surroundings Endothermic Reaction: Reaction that absorbs heat from surroundings Exothermic Rxn Endothermic Rxn

  3. Practice: Identify each reaction as 1) exothermic or 2) endothermic A. N2 + 3H2 2NH3 + 22 kcal B. CaCO3 + 133 kcal CaO + CO2 C. 2SO2 + O2 2SO3 + heat Exo Endo Exo

  4. 1st law of thermodynamics: energy of the universe is constant Enthalpy: heat energy; change in heat energy from reactants to products is DHo Spontaneous Process: Process that takes place without persuasion, without stimulus or energy input (Ball rolling downhill) Nonspontaneous Process: Process that requires energy or stimulus to occur (Ball being pushed uphill)

  5. Entropy: Measurement of disorder or randomness of a system; change in entropy from reactants to products is DSo 2nd law of thermodynamics: entropy of universe spontaneously tends to increase Kinetics Kinetics: study of the rate, or speed of chemical reactions Reaction Rate: Speed of a reaction; how quickly or slowly a reactant is used up or a product accumulates Activation energy: minimum amount of energy required to produce a chemical reaction

  6. Note the Activation Energy (Ea) in Exothermic and Endothermic Rxns Exothermic Rxn Endothermic Rxn

  7. Factors that Influence Reaction Rates • Structure of Reactants • Attraction between oppositely charged particles; breaking of covalent bonds; size of molecules • Concentration of Reactants • The greater the concentration of reactants, the more collisions leading to a reaction will occur • Temperature of Reactants • Increasing the temperature increases the kinetic energy of the particles, allowing more collision to occur

  8. Physical state of Reactants • Solid, liquid or gas • Presence of Catalysts • Catalyst: Substance that increases rate of a reaction without being used up in the reaction • Catalysts provide alternate way for reaction to occur, with a lower activation energy than the normal way

  9. Effect of Catalyst on Activation Energy With Catalyst (Lower Ea) Without Catalyst (High Ea)

  10. Chemical Equilibrium • Chemical reactions can go both directions • H2 + I2 2HI • Equilibrium: Condition when rate of forward reaction equals rate of reverse reaction • Equilibrium Concentrations: Unchanging concentrations of products and reactants in a reaction that is at equilibrium

  11. Equilibrium Position Can Change! • H2 + I2 2HI • Le Chatelier’s Principle: Equilibrium position will shift in response to changing conditions in such a way as to minimize or oppose changes • Note: Concentration of chemicals and heat will affect equilibrium; presence of a catalyst will not!

  12. Summary of Changes on Equilibrium

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