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Reaction Rates

Reaction Rates. Things that influence the rate of a reaction. Indicators of a Chemical Reaction. Gas produced (bubbles) Temperature change (gets hot or cold) Color change Precipitate formed Light given off. Reaction Rate. How fast a reaction happens

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Reaction Rates

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  1. Reaction Rates Things that influence the rate of a reaction

  2. Indicators of a Chemical Reaction Gas produced (bubbles) Temperature change (gets hot or cold) Color change Precipitate formed Light given off

  3. Reaction Rate • How fast a reaction happens • reactions depend on collision frequency and efficiency

  4. Factors that Affect Rate 1. Reactant Nature • what the reactant reacts with • Metal Reactivity • Mg in HClvs Cu in same solution

  5. 2. Temperature • more energy in the particles causes more collisions and more energy to make the reaction occur • Ex. Alka Seltzer balloon race

  6. 3. Concentration • more particles to react with; causes a faster reaction because of more collisions • Ex. Concentrated vs. dilute acid

  7. 4. Catalysts • catalyst - a substance that changes the reaction rate without being used up • Reactions require a certain amount of activation energy. • Catalysts LOWER the amount of activation energy needed (reaction happens more easily)

  8. 5. Surface Area • rxn occurs where two surfaces are in contact • Ex. Sugar (cube vs. powdered)

  9. LeChatlier’s Principle Chemical Equilibrium

  10. Chemical Equilibrium Reversible Reactions • Most reactions can occur in both directions Ex. 2SO2(g) + O2(g) ↔ 2SO3(g) • Chemical equilibrium – when the forward and reverse reactions are taking place at the SAME RATE • Does not mean the same amount of product and reactant, just that the concentrations are no longer changing. • Called DYNAMIC equilibrium… constantly shifting

  11. Irreversible Reactions • Some reactions go to completion and are not able to reverse • Gas formed – gas escapes. Can’t go backwards • Precipitate formed – insoluble product is formed…no ions left.

  12. Shifting Equilibrium • Le Chatelier’s principle – if a stress is applied to a system at equilibrium, the system changes to relieve that stress • Like a see-saw… If more is applied to one side, the other adjusts to maintain equilibrium

  13. Endothermic Reactions • Energy is used to begin a reaction • Products have higher energy than reactants • Absorbs heat from surroundings • Ice melting • Water evaporating

  14. Exothermic Reactions • Gives off energy during a reaction • Reactants have more energy than products • Gives off heat • Ice freezing • Water condensing

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