Rates of ReactionRates of Reaction

Prentice-HallPrentice-Hall

Chapter 18.1Chapter 18.1

ObjectivesObjectives

DescribeDescribe how to express the rate of a how to express the rate of a chemical reaction.chemical reaction.

IdentifyIdentify four factors that influence the four factors that influence the rate of a chemical reaction.rate of a chemical reaction.

The heat given off by the corrosion The heat given off by the corrosion reaction of an iron-magnesium alloy reaction of an iron-magnesium alloy with salt water can produce a hot with salt water can produce a hot meal. meal.

Rate of ReactionRate of Reaction

In chemistry, the rate of chemical In chemistry, the rate of chemical change, or the reaction rate, is usually change, or the reaction rate, is usually expressed as the amount of reactant expressed as the amount of reactant

changing per unit time.changing per unit time.

Key Idea

A A raterate is a measure of the speed is a measure of the speed of any change that occurs within of any change that occurs within

an interval of time.an interval of time.

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

Collision TheoryCollision Theory

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

Effective Collision

Ineffective Collision

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

activation energyactivation energy..

An An activated complexactivated complex is an is an unstable arrangement of atoms that unstable arrangement of atoms that forms momentarily at the peak of the forms momentarily at the peak of the activation-energy barrier. activation-energy barrier.

The activated complex is sometimes The activated complex is sometimes called the called the transition statetransition state..

TemperatureTemperature ConcentrationConcentration Particle size Particle size Use of a catalystUse of a catalyst

Factors Affecting Reaction Rates

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

ConcentrationConcentrationa) In air, a lighted splint glows and soon goes out.a) In air, a lighted splint glows and soon goes out.

b) When placed in pure oxygen (higher oxygen b) When placed in pure oxygen (higher oxygen concentration), the splint bursts into flame.concentration), the splint bursts into flame.

Particle SizeParticle SizeThe minute size of the reactant particles (grain The minute size of the reactant particles (grain dust), and the mixture of the grain dust with dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be oxygen in the air caused the reaction to be explosive, destroying the grain elevator.explosive, destroying the grain elevator.

Catalysts

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.

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

a)a) mmol/s.mmol/s.

b)b) mol/L.mol/L.

c)c) kJ/mol.kJ/mol.

d)d) h/mol.h/mol.

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

a)a) mmol/s.mmol/s.

b)b) mol/L.mol/L.

c)c) kJ/mol.kJ/mol.

d)d) h/mol.h/mol.

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.

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.

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

a)a) temperaturetemperature

b)b) concentration of reactantsconcentration of reactants

c)c) total mass of reactantstotal mass of reactants

d)d) surface area of reactantssurface area of reactants

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

a)a) temperaturetemperature

b)b) concentration of reactantsconcentration of reactants

c)c) total mass of reactantstotal mass of reactants

d)d) surface area of reactantssurface area of reactants

4. A catalyst works because it 4. A catalyst works because it

a)a) lowers the activation energy.lowers the activation energy.

b)b) increases the temperature.increases the temperature.

c)c) is permanently changed in a is permanently changed in a reaction.reaction.

d)d) supplies energy to a reaction.supplies energy to a reaction.

4. A catalyst works because it 4. A catalyst works because it

a)a) lowers the activation energy.lowers the activation energy.

b)b) increases the temperature.increases the temperature.

c)c) is permanently changed in a is permanently changed in a reaction.reaction.

d)d) supplies energy to a reaction.supplies energy to a reaction.