Chemical Change: Energy, Rate and Equilibrium Thermodynamics: study of energy, work and heat Kinetic energy: energy of motion Potential energy: energy.

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Presentation transcript:

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 + O 2  2H 2 O + energy

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

Practice: Identify each reaction as 1) exothermic or 2) endothermic A. N 2 + 3H 2 2NH kcal B. CaCO kcal CaO + CO 2 C. 2SO 2 + O 2 2SO 3 + heat Exo Endo

1 st law of thermodynamics: energy of the universe is constant Enthalpy: heat energy; change in heat energy from reactants to products is  H o 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)

Entropy: Measurement of disorder or randomness of a system; change in entropy from reactants to products is DS o 2 nd 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

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

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

 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

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

Chemical Equilibrium Chemical reactions can go both directions H 2 + I 2 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

Equilibrium Position Can Change! H 2 + I 2 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!

Summary of Changes on Equilibrium