Chemical Kinetics – study of the rates of chemical reactions Some reactions we would like to speed up Some reactions we would like to slow down

What are 4 ways to change the rate of a chemical reaction? Link #1 Link #2 Link #3 Link #4

How can we change the rate of chemical reactions? Change Concentration (or pressure of gases) Change Surface area of a solid video link Change Temperature Add a catalyst

Increasing Concentration Increases # of Collisions Link to Collision Theory Animation II

For each pair of pictures which reaction will be faster and why? Increasing surface area of solids increases reaction rate by increasing number of collsions

Which set of conditions high pressure or low pressure will produce a faster reaction between gases and why? INCREASING PRESSURE OF GASES INCREASES THE REACTION RATE BY INCREASING THE NUMBER OF COLLISIONS

Reactions need a minimum energy (activation energy, Ea) to occur Link to collision theory animation

Height of Ea determines rxn rate; smaller ea = more molecules that have enough energy to overcome ea = faster rxn

Impact of temperature on Reaction Rate ↑ Temp → ↑ ave speed → ↑ Energy of collisions % of molecules with Energy ≥ Ea increases at higher T Link to Phet Simulation

Catalysts accelerate reactions without being consumed by lowering the energy of activation Lower Ea = Faster rxn Enzyme link

Reaction requires collisions in the correct orientation The two specific atoms in the different molecules that are reacting have to collide Link to animation

Collision theory- atomic level explanation of reaction rates Requirements for a chemical Reaction: Collision between reacting molecules # of collisions can be increased by : i) Increasing concentration ii) Increasing surface area for solid reactants 2) Collision must have sufficient Energy Energy of collisions impacted by: i) Temperature, ↑ Temp → ↑ ave speed → ↑ Energy of collisions ii) Catalyst – speeds up reaction without being consumed by lowering energy of activation 3) Collisions must have correct orientation

Summary OF Collision Theory

Link to Phet Simulation Link to Collision Theory Animation II

Link to reaction profile diagram animation Link to collision theory animation

Chem Demos II – Chapter 22 – Iodine Clock (concentration and temperature) Chem Demos II Chapter 20 – Catalyst Surface Area- Demo with alka seltzer tablets Chem Demos Side 2 #1 Water Gas; #2 Hydrogen Chlorine Cannon; 2nd Day Rxn Profile Diagrams N2/I2