1. Rates of Chemical Reactions

2. Collision Model/Theory  Atoms and molecules can be considered similar to cars  They are constantly moving around and crashing into one another  When they move slowly: They simply bump off of one another and nothing happens  When they move quickly: Bonds holding atoms and molecules can break and new/different bonds will form This is what causes a chemical reaction or a chemical change to occur

3. Rates of Chemical Reactions Defined:  The rate of a chemical reaction is essentially the amount of time it takes for a successful reaction to occur  The rate of a chemical reaction is affected by the number of collisions of reactant atoms & molecules which result in new bonds or new molecules as products

4. How can you make a chemical reaction occur faster?  There are two (2) ways to make a chemical reaction occur faster: 1. Increase the number of collisions between atoms & molecules 2. Increase the number of effective collisions  This means making sure that the collisions that do occur actually give rise to new bonds and new products

5. Factors that affect the rate of chemical reactions  There are four (4) factors that affect the rate at which a reaction will take place  By changing any of these factors you can speed up or slow down a reaction

6. Factors that affect the rate of chemical reactions continued… 1. Temperature: - a) Increasing the temperature increases the rate of a chemical reaction: - Heat causes molecules & atoms to move faster which increases both the number of collisions and the effectiveness of these collisions - Example: Cooking food. Food cooks faster at higher temperatures - b) Decreasing the temperature decreases the rate of a chemical reaction: - A lower temperature slows down atoms & molecules and therefore there are less collisions and effective collisions - Example: Storage of food. We store uneaten food in fridges or freezers to slow down the chemical reaction of food decay. The lower temperature impairs the decay of food

7. Factors that affect the rate of chemical reactions continued… 2. Concentration: - concentration refers to the amount of atoms & molecules in a given space - a) Increasing the concentration increases the rate of a chemical reaction - when more atoms & molecules are packed into a small space, they are more likely to collide - Example: The hallways at WMCI at break. When there are more students trying to get to various location packed into the same sized hallway, it is difficult to avoid a collision - b) Decreasing the concentration decreases the rate of a chemical reaction - when there are less atoms & molecules packed into the same space, there is more room for them to move around without colliding - Example: The hallways at WMCI during class. There are a lot less students in the hallways at this time, so they are less likely to collide

8. Factors that affect the rate of chemical reactions continued… 3. Surface area: - the amount of area visible of a substance (atom & molecule) that is able to react - a) Increasing the surface area of an atom or molecule increases the rate of a chemical reaction - If there is a larger area of an atom or molecule available, there is a greater chance of a collision to occur - b) Decreasing the surface area of an atom or molecule decreases the rate of a chemical reaction - If there is a smaller area of an atom or molecule available, there is less of a chance for a collision to occur

9. Factors that affect the rate of chemical reactions continued… 4. Catalyst: - This is a chemical that helps a reaction or process occur faster - Catalysts are not used up in a reaction; they are not considered a reactant - When catalysts are added, the rate of a chemical reaction is increased because it has help - Example: Adding clear indicator to a chemical reaction to illustrate the color change