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Chapter 17, Section 1 p. 596-600

Chapter 17, Section 1 p. 596-600. Entropy and Your Bedroom. Low energy (allowed to spontaneously exist)  randomness and disorder increases High energy  clean and neat (order) It takes energy to defeat entropy. Entropy.

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Chapter 17, Section 1 p. 596-600

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  1. Chapter 17, Section 1 p. 596-600

  2. Entropy and Your Bedroom • Low energy (allowed to spontaneously exist)  randomness and disorder increases • High energy  clean and neat (order) • It takes energy to defeat entropy

  3. Entropy • Entropy (S) is a measure of the disorder or randomness of the particles that make up a system. • The Law of Disorder state that spontaneous processes always proceed in such a way that entropy of the universe increases. • It takes energy to clean your room. If allowed to spontaneously exist (low energy), disorder and randomness will take over. • Without the addition of energy, chemical reactions generally progress toward high entropy (greater disorder, lower energy)

  4. Which has higher entropy?Reactants or products? • NaCl(s) NaCl(aq) • Products (greater number of parts) • NaCl(s)  Na+ (aq) + Cl- (aq) • CaCO3(s) + HC2H3O2(aq)  Ca(C2H3O2)2(s) + CO2(g) + H2O(l) • Products (greater number of parts, and changing states to gas)

  5. Energy & Heat Energy – ability to produce heat Heat - (H) energy in the process of flowing from a warmer object to a cooler object. In chemical reactions this flow can be in either direction depending upon the type of reaction. Remember that a reaction is called a system. Anything outside the system is called the surroundings.

  6. Reaction Rates • Reaction Rate - the speed at which reactants become products • Activation Energy "Ea"-The Energy required to initiate a chemical reaction. Both endothermic and exothermic reactions require activation energy. • Activated complex - an unstable combination of reacting molecules that is intermediate between reactants and products. • Potential energy – stored energy

  7. 2H2(g) + O2(g) 2H2O (l) + energy H2O (g) H2O (l) + energy energy + 2HgO (s) 2Hg (l) + O2(g) energy + H2O (s) H2O (l) Exothermic process: heat is produced and released to surroundings Endothermic processheat is absorbed from surroundings

  8. Practice • Does the graph represent an endothermic or exothermic reaction • Determine the heat of reaction, ∆H,  for this reaction. • Determine the activation energy, Ea, for this reaction. • What is the energy of the activated complex for this reaction? • Determine the reverse activation energy, Ea for this reaction.

  9. Factors Affecting Reaction Rates: Concentration What do you think? (Think/pair/share) Q: When we have a high # of reactants, will the rate of reaction be higher or lower than with low # of reactants? A: As the concentration of the reactants increases, the reaction rate increases. WHY? According to the collision theory, the rate of a reaction is directly proportional to the number of effective collisions per second between the reactant molecules. Effective Collisions - the fraction of total collisions that actually result in the formation of the product(s). If the concentration of the reactants increases (i.e. particles per given volume) the greater the number of total collisions. The greater the frequency of total collisions, the greater the frequency of effective collisions. If the frequency of effective collisions increases, so does the reaction rate.

  10. Factors Affecting Reaction Rates: Surface Area What do you think? (Think/pair/share) Q: As the surface area of reactants increases, will reaction rate increase or decrease? A: As the surface area of the reactants increases, the reaction rate increases. WHY? Increasing the surface area of the reactants results in a higher number of reaction sites. Reaction sites - specific sites on molecules at which reactions occur. • Increasing the number of reaction sites increases the number of total collisions. • The greater the frequency of total collisions, the greater the frequency of effective collisions. • If the frequency of effective collisions increases, so does the reaction rate.

  11. Factors Affecting Reaction Rates: Temperature What do you think? (Think/pair/share) Q: As the temperature of a system increases, will the reaction rate increase or decrease? A: As the temperature of a system increases, the reaction rate increases. WHY? Temperature (T) - A measure of the average kinetic energy (KEavg) of the particles of a substance. Increasing T increases KEavg. At higher T, the fraction of molecules with energies greater than the activation energy (Ea) increases.

  12. Factors Affecting Reaction Rates: Catalysts What do you think? (Think/pair/share) Q: Will the presence of a catlyst increase or decrease reaction rates? A: The presence of a catalyst increases the reaction rate by lowering the activation energy of a reaction. WHY? Catalyst - A substance that increases the rate of a reaction but is not consumed in the reaction.

  13. Biological catalyst =? • Enzyme – protein that increases speed of reactions in organisms (usually end in “-ase”) • Example: • Lactase helps you break down the milk sugar lactose

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