1. Unit 10: Energy in Chemical Reactions
Cypress Creek High School
Chemistry 1L
Chapter 10

2. Reaction Rate
Reaction Rate is the number of atoms, ions or molecules that react in a given time to form products
We measure either the rate of disappearance of the reactants or the rate of appearance of one of the products
In simpler terms:
The average rate is the change in a given quantity during a specific period of time. 2

3. Reaction Rate Graph For the reaction H2 + I2 → 2HI,
What is happening to the concentration of the reactants?
What is happening to the concentration of the products? 3

4. Measuring Reaction Rates
Change in Electrical Conductivity
Change in Color
Change in Pressure
Change in Volume 4

5. Factors that Effect Reaction Rate
Physical State of the Reactants
The more freedom of movement, the more collisions
As state of matter changes from solid to gas, rate increases

6. Factors that Effect Reaction Rate
Concentration of Reactants
The more particles, the more collisions
As concentration increases, rate increases 6

7. Factors that Effect Reaction Rate
Temperature of Reactants
As temperature increases, particles move faster; there are more high-energy collisions 7

8. Factors that Effect Reaction Rate
Particle Size (surface area)
For solids, breaking up big pieces increases surface area, increasing rate by having more places for the molecules to interact
Ionic compounds have more surface area than covalent 8

9. Factors that Effect Reaction Rate
Pressure – Gases only!
As pressure increases the concentration increases, so you will have more collisions 9

10. Factors that Effect Reaction Rate
Catalysts – compounds added to speed up reaction but not used in the reaction.
Lowers activation energy but does not change ΔH
Examples: enzymes, catalytic converters (Pt, plates that convert NO → N2 + O2 and CO → CO2) 10

11. Catalyst 11

12. Catalysts
Without a
catalyst
Enthalpy
Time (min)

13. Catalysts Lowers activation Without a energy catalyst Enthalpy With a
Time (min)

14. Catalysts DOES THE CATALYST CHANGE THE DH? NO! Lowers activation
energy
Without a
catalyst
Enthalpy
H reactants
With a
catalyst
H products
Time (min)

15. Factors that Effect Reaction Rate
Inhibitors
Compounds added to a reaction that slow it down
Examples: Lead in diesel, preservatives in food. 15

16. Reaction Rates Discussion
Why do you add lighter fluid to charcoal in a grill?
How does opening and closing air vents on a charcoal grill effect how fast the coals burn?
How can an explosion occur in a grain elevator when grain is not considered flammable? 16

17. Chemical Reactions Example
Remember the classic science fair project - the homemade volcano?
It’s done by combining vinegar and baking soda (and some red food coloring for effect).
These substances undergo a chemical reaction, evident by the overflow and bubbles.
This reaction produces three new substances: water, carbon dioxide, and sodium acetate (used in hot packs)
Reaction of baking soda and vinegar: