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Kinetics & Equilibrium

Kinetics & Equilibrium. Aim: How do you determine if a reaction will happen?. Factors that Change During A Reaction. Energy( H) = Enthalpy Nature favors a change to lower energy In what type of reaction is there a decrease in energy? Exothermic

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Kinetics & Equilibrium

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  1. Kinetics & Equilibrium Aim: How do you determine if a reaction will happen?

  2. Factors that Change During A Reaction Energy( H) = Enthalpy Nature favors a change to lower energy In what type of reaction is there a decrease in energy? Exothermic Most Exothermic reactions take place spontaneously. Do any Endothermic reactions take place spontaneously? An ice cube must absorb heat to melt, but it melts anyway. (bc heat flows high  low)

  3. Factors that Change During A Reaction What also changes when ice melts? H2O(s)H2O(l) The state it is in and the motion of the molecules. Entropy (ΔS)-The degree of randomness or disorder. Ex- What happens to the disorder after you drop a box of marbles or watch your room for a week? It increases Nature favors an increase in entropy.

  4. How Do You Determine What Happens To Entropy ? A solid has an orderly arrangement and low entropy. A liquid has the molecules next to each other but moving slowly therefore medium entropy. A gas has molecules moving all over the place and high entropy. Write down: SL G Increases Decreases

  5. SummaryEntropy Increases When... • Reactions of solids produce gases or liquids, or liquids produce gases. • A substance is divided into parts; reactions with more products than reactants have an increase in entropy. (Decomposition) • The temperature increases- because the random motion of the molecules is increased. • A solid is dissolved (aq).

  6. What Happens To Entropy In The Following Reactions ? 1. 2KClO3(s) 2KCl (l) + 3 O2 (g) Increases 2. H2O(l) H2O(s) Decreases 3. NaCl (s) NaCl (aq) Increases

  7. What happens to energy and entropy in the following reactions ? 1. 2 H2(g) + O2 (g)  2H2O (l) + 457 kJ Energy decreases and Entropy decreases 2. NaCl(s) + 43 kJ Na+(aq) + Cl- (aq) Energy increases and Entropy Increases

  8. Spontaneity How can we predict if a reaction will happen ( be spontaneous)?

  9. Key Facts Spontaneous-Reactions that will happen. Non-spontaneous- Reactions that do not occur Two factors that influence if a reaction takes place are: • Enthalpy (energy) ΔH and entropy ΔS(disorder) • The favored changes are: • + ΔS (increasing disorder) • -- ΔH (decreasing/giving off energy).

  10. How can the factors be used to predict if a reaction is spontaneous ? • A change with + ΔS & -- ΔH is always spontaneous. • A change with – ΔS & + ΔH is never spontaneous. • A change with – ΔS & -- ΔH is maybespontaneous. • A change with + ΔS & + ΔH is maybespontaneous. To predict, use Gibbs Free Energy Formula *Note: you would be provided a table with ΔS and ΔH values in order to solve the following equation.

  11. Gibbs Free Energy Equation- formula used to predict if a reaction is spontaneous • ΔGº (Free Energy)= ΔHº - TΔSº (Temperature must be in Kelvin) • All spontaneous reactions release free energy and therefore have a -- ΔG. • ΔG = (-) for a spontaneous reaction. • ΔG = (+) for a non- spontaneous reaction. • ΔG = (0) for a reaction @ equilibrium

  12. + - - + + - - - - - + + ΔG=ΔH-TΔS Spontaneous ΔS ΔH ΔG At all Temperatures Only at high temperatures “entropy driven” Only at low temperatures, “enthalpy driven” Not at any temperature,

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