Chapter 17 “Reaction Rates and Equilibrium” Part 1: Reaction Rates Activation Energy is being supplied Activated Complex Reaction Rates #1.ppt

Today you will learn… How particle collisions affect reaction rate How particle collisions affect reaction rate Definitions of activation energy, activated complex / transition state Definitions of activation energy, activated complex / transition state What factors affect reaction rate What factors affect reaction rate Effects of temperature on reaction rate Effects of temperature on reaction rate

Collision Theory Reactions can occur: Very fast – such as a firecracker Very slow – such as the time it took for dead plants to make coal Moderately – such as food spoilage

Collision Theory A “rate” is a measure of any change that occurs within an interval of time (speed is not the same thing as rate… speed is one kind of rate) In chemistry, reaction rate is expressed as the amount of reactant changing per unit time. Example: 3 moles/year, or 5 grams/second

I wonder what happens if I mix these two solutions…

I wonder if I should be wearing my goggles?

WOW, that was really FAST

It was also really FUN

Collision Model Key Idea: The molecules must touch (or collide) to react. However, only a small fraction of collisions produces a reaction. Why? Particles lacking the necessary kinetic energy to react will bounce apart unchanged when they collide… think of a velcro wall!

Collision Model   Collisions must have enough energy to produce the reaction: must equal or exceed the “activation energy”, which is the minimum energy needed to react.   Will a AA battery start a car? Think of clay clumps thrown together gently – they don’t stick, but if thrown together forcefully, they stick tightly to each other.

Collision Model An “activated complex” is an unstable arrangement of atoms that forms momentarily (typically about seconds) at the peak of the activation- energy barrier. Also called the transition state Results in either a) forming products, or b) reformation of reactants

- Page 543 a. Reactants b. Absorbedc. No; it could also revert back to the reactants

Collision Model The collision theory explains why some naturally occurring reactions are very slow Carbon and oxygen react when charcoal burns, but this has a very high activation energy C + O 2(g) → CO 2(g)  H = kJ) C + O 2(g) → CO 2(g)  H = kJ) At room temperature, the collisions between carbon and oxygen are not enough to cause a reaction

Factors Affecting Rate 1) Temperature Increasing temperature increases the rate of a reaction. 2) Surface Area Increasing surface area increases the rate of a reaction 3) Concentration – Increasing concentration increases the rate of a reaction inhibitor 4) Presence of Catalyst – increases the rate unless an inhibitor is present

Temperature When we increase the temperature we give the particles energy When we increase the temperature we give the particles energy This makes them move faster This makes them move faster This means they collide with other particles more often This means they collide with other particles more often So the reaction goes faster. So the reaction goes faster.

Temperature Increasing temperature increases KE Increasing temperature increases KE Increasing KE means more particles have sufficient energy to overcome the activation energy barrier Increasing KE means more particles have sufficient energy to overcome the activation energy barrier

Temperature Demo: Demo: Spread of mixture in cold water vs. warm water Spread of mixture in cold water vs. warm water