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
Energy
Reactants
Activation
Energy Minimum energy
to make the
reaction happen
– how hard
Products
Reaction coordinate
Energy
Activated
Complex or
Transition State
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
2. Temperature
• more energy in the particles
causes more collisions and
more energy to make the
reaction occur
• Ex. Alka Seltzer balloon race
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.
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