1. Reaction Rates (Reactions occur due to COLLISIONS)
Chemical reaction rates depends on factors that influence the frequency of collisions between reactant molecules.
The rate of reaction = the decrease in concentration of reactants OR the increase in concentration of products within a given time interval.
(change in concentration / time)

2. Reaction Rates (Reactions occur due to COLLISIONS)
Reaction rates depend on factors such as:
Temperature (↑ temp. = ↑ rxn rate)
Concentration (↑ conc. = ↑ rxn rate)
Particle size (smaller size. = ↑ rxn rate)
Catalyst (with catalyst. = ↑ rxn rate)
Pressure (↑ pressure. = ↑ rxn rate) (DEPENDS)
Catalysts play a role in increasing the reaction rate by changing (lowering) the activation energy in a chemical reaction.

3. Collision Theory How is the rate of a chemical change expressed?
18.1
Collision Theory
Collision Theory
How is the rate of a chemical change expressed?
In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time.
(change in concentration / time)

4. 18.1
Collision Theory
A rate is a measure of the speed of any change that occurs within an interval of time.
(distance traveled / time)
(change in concentration / time)
Speed is measured as a change in distance in a given interval of time. A world-class sprinter might cover 100 meters in 11.5 seconds; the speed, or rate, is 100 m/11.5 s = 8.70 m/s.
(food eaten / time)
(questions answered / time)

5. 18.1
Collision Theory
Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.
As time passes, the amount of reactant (red squares) decreases and the amount of product (blue spheres) increases. Rates of chemical reactions are often measured as a change in the number of moles during an interval of time. Interpreting Diagrams Assuming equal time intervals between the boxes, how can you tell that the rate of conversion of reactant to product is not constant throughout this reaction?

6. IF there is enough energy
18.1
Collision Theory
According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy.
(Reactions occur due to COLLISIONS)
IF there is enough energy

7. (Reactions occur due to COLLISIONS) NOT enough energy = NO Reaction
18.1
Collision Theory
Ineffective Collision
(Reactions occur due to COLLISIONS)
NOT enough energy = NO Reaction
(orientation is also a factor)
If colliding particles have enough kinetic energy and collide at the right orientation, they can react to form a new product. a) An effective collision of reactant molecules produces product molecules. b) An ineffective collision of reactant molecules produces no reaction, and the reactants bounce apart unchanged.

8. (Reactions occur due to COLLISIONS) Enough energy = YES Reaction
18.1
Collision Theory
Effective Collision
(Reactions occur due to COLLISIONS)
Enough energy = YES Reaction
(orientation is also a factor)
If colliding particles have enough kinetic energy and collide at the right orientation, they can react to form a new product. a) An effective collision of reactant molecules produces product molecules. b) An ineffective collision of reactant molecules produces no reaction, and the reactants bounce apart unchanged.

9. Chemicals react to obtain a lower energy state (more stable)
18.1
Collision Theory
The minimum energy that colliding particles must have in order to react is called the activation energy.
Energy of Reactants
Chemicals react to obtain a lower energy state (more stable)
The activation-energy barrier must be crossed before reactants are converted to products. INTERPRETING GRAPHS a. Navigate Which are at a higher energy, the reactants or products? b. Read Is energy absorbed or released in progressing from the reactants to the activated complex? c. Interpret Once the activated complex is formed, will it always proceed to form products? Explain.
Energy of Products

10. The activated complex is sometimes called the transition state.
18.1
Collision Theory
An activated complex is an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier.
The activated complex is sometimes called the transition state.

11. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
Factors Affecting Reaction Rates
What four factors influence the rate of a chemical reaction?

12. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst (and pressure).

13. Factors Affecting Reaction Rates
Animation 22
Explore several factors that control the speed of a reaction.

14. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
Temperature
Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action.
Refrigeration Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action. Meat kept at freezing temperatures has a lifetime of months.

15. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
Concentration
a. In air, a lighted splint glows and soon goes out.
b. When placed in pure oxygen (higher oxygen concentration), the splint bursts into flame.
The rate of a reaction depends upon the concentrations of the reactants. a) In air, a lighted splint glows and soon goes out. b) When placed in pure oxygen, the splint bursts into flame. Inferring What accounts for the difference in reactivity?

16. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
Particle Size (and SURFACE AREA)
The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive, destroying the grain elevator.
An explosion destroyed this grain elevator. The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive.

17. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
Catalysts
A catalyst increases the rate of a reaction by lowering the activation-energy barrier. INTERPRETING GRAPHS a. Navigate How does the catalyst affect the magnitude of the activation energy? b. Read Does the catalyst change the amount of energy released in the reaction? c. Interpret Along which of the two reaction paths are reactants converted more rapidly to products?

18. Factors Affecting Reaction Rates
18.1
Factors Affecting Reaction Rates
An inhibitor is a substance that interferes with the action of a catalyst. Antioxidants and antimicrobials used in drying fruits and preserving fruit juices slow the action of microbes and limit contact with air.

19. 18.1 Section Quiz.
1. The units below that would be appropriate to measure the rate of a chemical reaction is
mmol/s.
mol/L.
kJ/mol.
h/mol.

20. 18.1 Section Quiz.
2. In a chemical reaction, the energy of reactants is always
greater than the energy of the products.
more than the activation energy.
less than the activation energy.
less than the energy of the products.

21. 18.1 Section Quiz.
3. An increase in which one of the following will NOT increase the reaction rate?
temperature
concentration of reactants
total mass of reactants
surface area of reactants

22. 18.1 Section Quiz.
4. A catalyst works because it
lowers the activation energy.
increases the temperature.
is permanently changed in a reaction.
supplies energy to a reaction.