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

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:

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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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