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Topic: Kinetics & Equilibrium. Aim: What are factors that affect rates of reaction? Do now: How do you think you can speed up a chemical reaction? HW :. Kinetics. describes rates (speed) and mechanisms (steps) of a rxn. Collision Theory.
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Topic: Kinetics & Equilibrium Aim: What are factors that affect rates of reaction? Do now: How do you think you can speed up a chemical reaction? HW:
Kinetics • describes rates(speed) and mechanisms (steps) of a rxn
Collision Theory • For a rxn to take place, must have successful collisions • Break old bonds, form new bonds • Particles need enough ENERGY and COLLIDEat the correct ANGLES.
Collision Theory • Unsuccessful collisions? • Insufficient energy • Insufficient location of collision
Factors, cont. • Temperature • Increase temp, __ KE , __ speed, force, & frequency of collisions • Example: low speed in parking lot vs. high speed on highway • Surface Area • Tiny particles (powders vs. cubes or sheets) have more SA • Larger SA, more exposed particles to collide, faster rate • Example: Powdered Mg in HCl will react faster than a solid piece of Mg because the powdered Mg has more surface area.
Factors Affecting Rxn Rate • Concentration • Greater # of particles/closer together in the container • ___ frequency of collisions • Gases - Different way to increase concentration w/o adding particles… • Shrink container • increases pressure • forces molecules closer • increases frequency of collisions & rate of rxn
Factors, cont. • Nature of Reactants/Complexity of Bonds • Rxns involving least # of bond rearrangements (breaking and making new bonds) are fast. • Ionic substances react fast • Ions just move close to each other and collide at any angle. • Rxns in (aq) fast b/c particles are already separated
Factors, cont. • Covalent slower b/c ANGLES are important • Esp. organic cpds – typically large mlcls, complex bonds • Example: Hydrogen and Oxygen = Water, it is polar and this is because bonds are broken and new ones are formed. The particles must collide at the right angle. This rxn is SLOW!
Factors, cont. • Catalyst • Speed up rxn w/o being used up • lowers activation energy • amount of energy needed to start a reaction • Provides alternate pathway that uses less energy • Faster rate of reaction • Particles need less energy to react
Sample Questions 1. Which conditions will increase the rate of the chemical reaction? (1) decrease temperature and decreased concentration of reactants (2) decrease temperature and increased concentration of reactants (3) increase temperature and decreased concentration of reactants (4) increase temperature and increased concentration of reactants 2. As the number of moles per liter of a reactant in a chemical reaction increases, the number of collisions between the reacting particles? (1) decrease (2) increase (3) remains the same
3. Which statement explains why the speed of some chemical reactions is increased when the surface area of the reactant is increased? • (1) this change increases the density of reactant particles • (2) this change increases the concentration of the reactant • (3) this change exposes more reactant particles to a possible collision • (4) this change alters the electrical conductivity of the reactant particles • Given the reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) • The reaction occurs more rapidly when a 10g sample of Mg is powdered, rather than in one piece, because the powdered Mg has • (1) less surface area (3) a lower potential energy • (2) more surface area (4) a higher potential energy
5. As the number of effective collisions between the reactant particles in a chemical reaction decreases, the rate of the reaction (1) decreases (2) increases (3) remains the same
