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)(change in concentration / time)

Reaction Rates (Reactions occur due to COLLISIONS)(Reactions occur due to COLLISIONS)

Reaction Rates (Reactions occur due to COLLISIONS)(Reactions occur due to COLLISIONS)Reaction rates depend on factors such as:1)Temperature (↑↑ temp. = ↑↑ rxn rate)2)Concentration (↑↑ conc. = ↑↑ rxn rate)3)Particle size (smallersmaller size. = ↑↑ rxn rate)4)Catalyst (with catalystwith catalyst. = ↑↑ rxn rate)5)Pressure (↑↑ pressure. = ↑↑ rxn rate) (DEPENDSDEPENDS)

Catalysts play a role in increasing the reaction rate by changing (lowering) the activation energy in a chemical reaction.

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Rates of Reaction >

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Collision Theory

Collision Theory

How is the rate of a chemical change expressed?

18.1

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)

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>Rates of Reaction18.1 Collision Theory

A rate is a measure of the speed of any change that occurs within an interval of timean interval of time.

(change in concentration / time)

(distance traveled / time)

(food eaten / time)

(questions answered / time)

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>Rates of Reaction

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Collision Theory

Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.

18.1

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>Rates of Reaction Collision Theory

According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, provided that provided that the colliding particles have enough kinetic the colliding particles have enough kinetic energyenergy.

18.1

(Reactions occur due to COLLISIONS)(Reactions occur due to COLLISIONS)

IFIF there is enough there is enough energyenergy

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>Rates of Reaction

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Collision Theory

Ineffective Collision

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(Reactions occur due to COLLISIONS)(Reactions occur due to COLLISIONS) NOT enough energy = NO ReactionNOT enough energy = NO Reaction (orientation is also a factor)

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>Rates of Reaction

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Collision Theory

Effective Collision

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(Reactions occur due to COLLISIONS)(Reactions occur due to COLLISIONS) Enough energy = YES ReactionEnough energy = YES Reaction (orientation is also a factor)

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>Rates of Reaction Collision Theory

The minimum energy that colliding particles must have in order to react is called the activation energy.

18.1

Energy of Energy of ReactantsReactants

Energy of Energy of ProductsProducts

Chemicals react to obtain a lower energy state (more stable)

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>Rates of Reaction 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.

18.1

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Rates of Reaction >

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Factors Affecting Reaction Rates

Factors Affecting Reaction Rates

What four factors influence the rate of a chemical reaction?

18.1

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Rates of Reaction >

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Factors Affecting Reaction Rates

The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst (and pressure).

18.1

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Rates of Reaction >

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Factors Affecting Reaction Rates

Animation 22

Explore several factors that control the speed of a reaction.

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>Rates of Reaction Factors Affecting Reaction Rates

Temperature

Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action.

18.1

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>Rates of Reaction 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.

18.1

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>Rates of Reaction 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.

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>Rates of Reaction Factors Affecting Reaction Rates

Catalysts

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>Rates of Reaction 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.

18.1

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18.1 Section Quiz.

1. The units below that would be appropriate to measure the rate of a chemical reaction is

a. mmol/s.

b. mol/L.

c. kJ/mol.

d. h/mol.

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18.1 Section Quiz.

2. In a chemical reaction, the energy of reactants is always

a. greater than the energy of the products.

b. more than the activation energy.

c. less than the activation energy.

d. less than the energy of the products.

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18.1 Section Quiz.

3. An increase in which one of the following will NOT increase the reaction rate?

a. temperature

b. concentration of reactants

c. total mass of reactants

d. surface area of reactants

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18.1 Section Quiz.

4. A catalyst works because it

a. lowers the activation energy.

b. increases the temperature.

c. is permanently changed in a reaction.

d. supplies energy to a reaction.