Reaction Rates Notes#12 Chapter 17

Reaction Processes & Rates Reactions are written in simplified forms-showing reactants turning into products reactants → products Real reactions are more complex Elevated energy states, and temporary substances (activated complex) are the rule Some reactions → more complex→ several distinct steps

Reaction Rates Chemical reaction rates vary widely Some reactions are completed within a few milliseconds Others require thousands of years Most Reactions start off relatively rapidly, slow steadily, and become very slow as they approach completion Some reactions simply stop at completion. Others level out at an equilibrium with their reverse reactions (forward & reverse rates equal)

Reaction rate Average rate at which reactants produce products CO(g) + NO2(g) → CO2(g) + NO(g) Reaction rate =∆quantity ∆time Time (s) [NO] (M) 0.00s 0.00 2.00s .010

Pg. 531 Practice problems 1,3

Collision Theory Explains chemical reactions in terms of effective collisions between particles. -sufficient energy -favorable orientation Conditions that favor effective collisions, favor reactions. Increasing Temperature (& pressure) increase the frequency & energy of collisions… favoring most reactions

Activation Energy, Activated Complexes Most physical & chemical changes require an input of energy to breakdown older structures Bonds within reactants are broken down with a specific amount of energy called Activation Energy . Activation energy – is amount of energy to activate the reaction, get it going energized, broken down reactants → temporary activated complexes → products

Activated Complexes Reactants+EnergyActivated complex Internal Energy ‘Peaks’ in this complex, then starts to drop as more stable products begin forming. Activated Complex  Products + Energy Draw 2 graphs

Reaction Rates (5 factors affecting rates) 1. Substances involved & Reaction Type * Ions in solution react very fast * Most metals corrode slowly 2. Temperature = Kinetic Energy higher temp. speeds up most reactions 3. Concentration reactions go faster at higher concentrations (more effective collisions)

Reaction Rates (5 factors affecting rates) Continued 4. Contact Area (surface area, mixing) fine powder, versus large pellets into liquid 5. Catalysts-substances that promote or speed up reactions without themselves being consumed. Catalysts lower activation energy. Enzymes are a type of catalyst