Chemical Reaction Rates

Unit 6 – Chemical Reaction

A note about rates…

What is rate? (think about driving a car)

The rate is how fast/slow something happens over time

The rate does not mean how fast it will take to finish EVERYTHING

Collision Theory

The collision theory states that the rate of a chemical reaction depends on how many collisions (bumps) the atoms make with each other.

What are some things that we, as the scientist, can do to make more of these collisions happen?

Chemical Reaction Rates

Reaction Rate Factor

What is it? What happens?

Example

Concentration How many atoms there are at the beginning of the reaction. Ex. Higher concentration means more atoms

More atoms means more chances for collisions. When we add atoms, the reaction rate increases

Surface Area The amount of area there is for the chemical reaction to occur. Ex. How much space there is

When there are more “spots” for the reaction to occur, the reaction rate increases

Chemical Reaction Rates, cont’d

Reaction Rate Factor

What is it? What happens?

Example

Temperature Measure of kinetic energy of the atom. The higher the temperature, the higher the kinetic energy

The atoms move faster and as they move faster they collide into things more often increasing the reaction rate.

Catalyst A substance that helps the reaction rate. It does not get “used” up in the reaction.

Catalysts bring the atoms together more often to increase the chances of a collision. Using a catalyst increases the reaction rate

Practice:

1. Which of the following will increase the rate of a reaction?

a. Breaking solid reactants into smaller pieces

b. Removing the catalyst

c. Decreasing the temperature

d. Decreasing the concentration

Real-world connection example

You are studying for your quiz next week…here’s an example of this situation in a chemical reaction:

Student + studying “A” on Quiz

1. What are the reactants in this reaction?

2. What are the product(s) in this reaction?

3. Name 3 catalysts that would help you receive an A …(what would make studying easier?)

Practice #2.

2. Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas as shown by the reaction below:

Zn + 2 HCl -> ZnCl2 + H2

Which of these actions would most likely decrease the rate of the reaction?

a. Remove the Zn from the reactants

b. Add a catalyst to the container of the reaction

c. Increase the temperature of the reaction

d. Increase the concentration HCl from the reactants