How Fast Does the Reaction Go? Reaction Rate How Fast Does the Reaction Go?

Collision Theory In order to react molecules and atoms must touch each other. They must be in the correct orientation. They must hit each other hard enough to react. Must break bonds Anything that increases how often and how hard will make the reaction faster.

Energy Reactants Products Reaction coordinate

Activation Energy - Minimum energy to make the reaction happen – how hard Reactants Products Reaction coordinate

Activated Complex or Transition State Energy Reactants Products Reaction coordinate

Activation Energy Low activation energy Lots of collision are hard enough fast reaction High Activation energy Few collisions hard enough Slow reaction

Reaction Rate How fast a reaction happens reactions depend on collision speed and orientation

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

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

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

4. Catalysts catalyst - a substance that changes the reaction rate without being used up Lowers the activation energy - allows the to reaction happen more easily.

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

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

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