Chapter 18.1

describe the reaction of carbon and oxygen

-Carbon and oxygen react when charcoal burns, but the reaction has a high activation energy. -The O—O and C—C bonds must be broken to form the activated complex. -At room temperature, the collisions of oxygen and carbon molecules are not energetic enough to break the bonds. -Thus, the reaction rate of carbon with oxygen at room temperature is essentially zero.

A catalyst is not Therefore, it does not appear as a _____________in the chemical equation. Instead, the catalyst is often written

-consumed during a reaction. -reactant -above the yield arrow

What happens to the particles at higher temperatures

-particles move faster The frequency of collisions increases along with the percentage of particles that have enough kinetic energy to slip over the activation-energy barrier. Thus, an increase in temperature causes products to form faster.

The lifetime of an activated complex is typically about

10-13 seconds.

is a measure of how much something changes within a specified amount of time.

A rate

is an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier.

An activated complex

is a substance that interferes with the action of a catalyst

An inhibitor

how does the activated complex end

Its brief existence ends with the reformation of the reactants or with the formation of products.

What four factors influence the rate of a chemical reaction?

Factors that can affect the rate of a chemical reaction are temperature, concentration, particle size, and the use of a catalyst.

How is the rate of a chemical reaction expressed?

In chemistry, the rate of a chemical reaction, or the reaction rate, is usually expressed as the change in the amount of reactant or product per unit time.

describe the progress of a typical reaction.

Over time, the amount of reactant decreases and the amount of product increases.

what happens if particles do not have enough energy

Particles that do not have enough energy to react bounce apart unchanged when they collide.

what happens when a catalyst is poisoned

Reactions slow or even stop when a catalyst is poisoned.

When salt water is added to the metal alloy in an MRE, the rate of the rusting reaction increases, and heat is produced rapidly. Which factor that can affect reaction rates is being applied in this situation?

Salt acts as a catalyst for the reaction between the metal and water, speeding up the reaction without being consumed.

when does the activated complex form (two reasons)

The activated complex forms only if the colliding particles have enough energy and if the atoms are oriented properly.

What factor determines whether a molecular collision results in a reaction?

The molecules must collide with enough energy in order to react. The minimum amount of energy needed is called the activation energy.

give an example of a fast reaction and of a slow reaction

When you strike a match, it erupts into flame almost instantly and burns quickly. Millions of years were required for plants buried beneath Earth's surface to be converted to coal.

particle size is the

The total surface area of a solid or liquid reactant affects the rate of a reaction.

How can rusting be used to cook a meal?

There are products that use the rusting of an iron-magnesium alloy to heat packaged food. These products are known as Meals Ready to Eat, or MREs for short.

An effective collision of oxygen and hydrogen molecules produces

water molecules.

An endothermic reaction does what

absorbs heat

When two reactant particles collide, they may form an

activated complex.

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

activation energy.

Catalysts permit reactions to proceed

along a lower energy path.

You can think of the activation energy for a reaction as a

barrier that reactants must cross before products can form.

why is the activated complex called the transition state

because of its brief existence

Some inhibitors work

by reaction with, or "poisoning," the catalyst itself.

Increasing the temperature is not always the best way to increase the rate of a reaction. A _____________is often better.

catalyst

According to __________________________, atoms, ions, and molecules can react to form products when they collide if the particles have enough kinetic energy.

collision theory

Cramming more particles into a fixed volume increases the

concentration of reactants, and, thus, the frequency of collision.

The activation-energy barrier must be ________________before reactants are converted to products.

crossed

Which of the following factors could be increased in order to decrease a reaction rate? A. Catalyst concentration B. Concentration C. Temperature D. Particle size

d

two ways to increase the surface area

dissolving, grinding it into a fine powder -In a solution, particles are separated and more accessible to other reactants. -Small dustlike particles, however, can be dangerous when suspended in air.

The catalysts that increase the rates of biological reactions are called

enzymes.

The tiny size of the reactant particles (sugar dust) caused the reaction of the sugar with oxygen in the air to be

explosive.

Collision theory explains why some reactions are

extremely slow at room temperature.

At normal body temperature (37C), reactions in the body

would be too slow without catalysts.

The smaller the particle size, the

greater the surface area is for a given mass of particles.

When you eat a meal containing protein, enzymes in your digestive tract

help break down the protein molecules in a few hours.

Increased collision frequency leads to a

higher reaction rate.

The result of an increase in surface area is an

increase in the frequency of collisions and the reaction rate.

catalyst is a substance that

increases the rate of a reaction without being used up during the reaction.

The activation-energy barrier for the catalyzed reaction is ________________ When the barrier is _____________, a

lower than that of the uncatalyzed reaction. greater fraction of reactants have the energy to form products within a given time.

Adding a catalyst speeds up a reaction by

lowering the activation energy.

An ineffective collision of oxygen and hydrogen molecules produces

no reaction; the reactants bounce apart unchanged.

A model called collision theory is used to relate the

properties of particles to the rates of chemical reactions.

exothermic reaction does what

releases heat.

Lowering the temperature usually

slows down a reaction.

raising the temperature

speeds up a reaction.

The rate of a chemical reaction can be controlled by adjusting

temperature, concentration, or particle size.

the inhibitor reduces

the amount of catalyst available for a reaction.

the activated complex is sometimes called the

transition state.

By __________________________________you can modify the rate of almost any reaction.

varying the conditions,

The speed of chemical reactions can vary from

very fast to extremely slow.

The number of particles in a given ______________affects the rate at which reactions occur.

volume (concentration)