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Reaction Rates and Equilibrium

Reaction Rates and Equilibrium. Chapter 18: Pages 541-585. Terms to know. Rate Collision theory Activation energy Inhibitor Catalyst Pressure Reversible reaction Equilibrium Dynamic equilibrium Le Chatelier’s principle. Collision Theory.

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Reaction Rates and Equilibrium

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  1. Reaction Rates and Equilibrium Chapter 18: Pages 541-585

  2. Terms to know • Rate • Collision theory • Activation energy • Inhibitor • Catalyst • Pressure • Reversible reaction • Equilibrium • Dynamic equilibrium • Le Chatelier’s principle

  3. Collision Theory • In order for chemical reactions to occur, particles must collide with a certain minimum amount of kinetic energy (activation energy). • Particles must also collide “head on.” Glancing collisions do not result in reactions. • As the chance of collisions increases, the chance of a chemical change (reaction) occurring increases correspondingly.

  4. Factors affecting collision Rate • Temperature: When particles are heated, the particles gain kinetic energy and move faster, increasing the chance of collision between reactant molecules. • Concentration and/or pressure: When particles are crowded together (Increased concentration or pressure), they are more likely to bump into each other so there is an increased chance of collisions. • Particle size: Smaller particles have more surface area (compared to volume) in order to achieve head on collisions that result in chemical reactions. • Let’s take a look!

  5. A Couple of Other factors affecting collision rates • Catalysts lower activation energy making it easier for particles to collide effectively. • Inhibitors (like food preservatives) make it so that catalysts don’t work; thus, slowing reducing effective collisions.

  6. Reversible Reactions • Some reactions occur in both directions at once. • In other words, reactants are making products at the same time the products are making reactants. • Forward reaction: • 2SO2 + O2 2SO3 • Reverse reaction: • 2SO3  2SO2 + O2 • Combined reaction: • 2SO2 + O2  2SO3

  7. Chemical Equilibrium • Remember reversible reactions… • 2SO2 + O2  2SO3 • At first, the reaction will occur in one direction more than the other • After some time, the rates of the forward and reverse reactions will equalize. • Chemical equilibrium is reached when the rates of the forward and reverse reactions equalize.

  8. Dynamic equilibrium • At equilibrium, the amounts of reactant and product reach a steady state, since the forward and reverse reaction rates are equal. • It is important to remember that the reactions haven’t stopped. They are happening at the same rate, so the amount of products and reactants stays the same. • Dynamic equilibrium means that the reactions are still happening (dynamic) but the amount of products and reactants are staying the same.

  9. Equilibrium Point • Chemical equilibrium occurs at the point when the forward and reverse reactions occur at the same rate. • This does not mean that there are equal amounts of reactants and products. • Equilibrium point is the amount of product and reactant present when a reaction is at chemical equilibrium. Sciencequiz.net

  10. Equilibrium means balance • Chemical equilibrium is a delicate balance. Just like a person responds to a push in order to keep balance, a chemical reaction does the same. • Le Chatelier’s Principle says that if a stress is applied to a reaction at equilibrium, the reaction responds in a way that relieves the stress. Uscerock.com

  11. Stresses on Equilibrium: Concentration • Concentration or amount: As you add more of a reactant or product to a reaction, the reaction will produce more of the other. 2SO2+ O2  2SO3 • If I add more SO2 and/or O2, the reaction will produce more SO3to relieve the stress. • If I add more SO3, the reaction will produce more SO2 and O2 to relieve the stress.

  12. Stresses on Equilibrium: Temperature • Temperature: As you add more heat, the reaction will respond in a way to reduce or give off heat. If you take away heat, the reaction will respond in a way to produce more heat. 2SO2 + O2  2SO3 + heat • If I add heat, the reaction will produce more SO2 and O2. • If I take heat away, the reaction will produce more heat and SO3

  13. Stresses on equilibrium: Pressure • Pressure: Changes in pressure only affect gaseous reactants and products in chemical reactions. • Increasing the pressure causes the reaction to respond in a way that will reduce the number of moles of gas. • Decreasing the pressure causes the reaction to respond in a way that increases the number of moles of gas. • N2(g) + 3H2(g)  2NH3(g) • If I increase the pressure, more NH3 will be produced since there are only 2 moles of it. • If I decrease the pressure, more N2 and H2 will be produced since there is more of it (1 + 3 = 4 moles).

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