CHAPTER 7Chemical Reactions

Burning is an example of a chemical reaction. When charcoal burns, the carbon in the charcoal reacts with oxygen in the air to produce carbon dioxide and heat.

7.1 Describing Reactions

Chemical EquationsA chemical reaction tells you the substances

present before and after a reaction○ __________-substances that undergo change○ __________-The new substances formed as

a result of that change

Using Equations to Represent Reactions Reactants _______ into products

Reactants Products______ + ______ ______________C + O2 CO2

Chemical ________ is a representation of a chemical reaction in which the reactants and products are expressed as _________.○ “Carbon and oxygen react and form carbon

dioxide”

Conservation of Mass Mass of the products is always _____ to the

mass of the reactants. French chemist Antoine Lavoisier (1743–1794),

developed the law of ______________ ______. The law of conservation of mass states that mass is

neither ______ nor ________ in a chemical reaction

Whether you burn one carbon atom or six carbon atoms, the equation used to describe the reaction is the same.

Balancing Equations

In order to show mass is conserved, the chemical equation must be _________.

N2H4 + O2 N2 + _ H2O

N 2 N 2

H 4 H 2 x___ =4

O 2 O 1 x ___=2

To balance a chemical equation, first _____ the atoms on each side of the equation.

Math Practice 1.Hydrogen chloride, or HCl, is an important

industrial chemical. Write a balanced equation for the production of hydrogen chloride from hydrogen and chlorine.

• 2.Balance the following chemical equations.

3.Ethylene, C2H4, burns in the presence of oxygen to produce carbon dioxide and water vapor. Write a balanced equation for this reaction

Balancing Rules

_________- the numbers that appear ________ the formulas. In the unbalanced equation above, the

coefficients are understood to be___When you change a coefficient, you ______

the amount of that reactant or product represented in the chemical equation.

As you balance equations, you should ______ change the ____________ in a formula

7.2 Types of Reactions

Just as you can classify matter into different types, you can classify chemical reactions into different typesSome general types of chemical reactions

are _________ reactions, ___________ reactions, ______________ reactions, ___________________ reactions, and ____________ reactions.

Synthesis (Combination)

+ Ex: 2Na + Cl2 2 NaCl

2H2 + O2 2H2O Two or more substances

react to form a _______substance.

Sodium metal reacts vigorously with chlorine to form sodium chloride, NaCl

Decomposition

+ Ex: 2H2O 2H2 + O2

CaCO3 CaO + CO2

A compound __________ into two or more simpler substances.

Single Replacement + + Ex: Cu + 2Ag(NO3) 2Ag + Cu(NO3)

K + 2H2O H2 + 2KOH One element takes the ____ of another element in a compound

A single-replacement reaction occurs when copper wire is submerged in a solution of silver nitrate.

Potassium reacts with water in a single-replacement reaction that produces hydrogen gas and potassium hydroxide.

Double Replacement + + Ex: Pb(NO3) 2 PbI2 + 2KNO3

CaCO3 + 2HCl CaCl2 + H2CO3 Two different compounds exchange ___________ and form two new

compounds.

When potassium iodide solution is poured into a solution of lead(II) nitrate, a double-replacement reaction takes place. Lead(II) iodide forms as a yellow precipitate.

Combustion Ex: CH4 + 2O2 CO2 + H2O A substance reacts _____ with

______, often producing heat and light.

Ex: 2H2 + O2 2H2ONotice that you could also classify

this reaction as the ________ of water. The classifications for chemical reactions sometimes _________

A Bunsen burner generates heat and light by the combustion of natural gas.

7.4 Reaction Rates

Reaction Rates- Rate at which reactants change into __________ over time.Reaction rates tell you how ____ a reaction

is going.That is, how fast the reactants are being

__________, how fast the products are being _______, or how fast energy is being absorbed or released

Factors Affecting Reaction Rates

1. Temperature- Generally, an _______ in temperature will ________ the reaction rate.Ex: You store milk in a refrigerator to ____

down the reactions that cause the milk to _____Increasing the temperature of a substance

causes its particles to move ______, on average. Particles that move faster are both more likely to ______ and more likely to _____. If the number of collisions that produce reactions increases, then the reaction rate ____________

Factors Affecting Reaction Rates 2. Surface Area- An ________ in surface

area ________ the exposure of reactants to one another.The smaller the particle size of a given mass,

the______is its surface area. An increase in surface area increases the

_______ of reactants to one another. The greater this exposure, the ____ collisions there are that involve reacting particles. With more collisions, more particles will _____. This is why increasing the surface area of a reactant tends to _______ the reaction rate.

Factors Affecting Reaction Rates

3. _____- Stirring the reactants will generally ________ the reaction rate. Collisions between the particles of the reactants are more likely to happenEx: A washing machine speeds up the

reaction by ______ the contents back and forth

Factors Affecting Reaction Rates 4. ____________- The more reacting particles

present, the ____ opportunities there are for ________ involving particles.For gases, concentration changes with __________. The

greater the pressure of a gaseous reactant, the _______ is its concentration, and the faster is the reaction rate.

The dye solution in the left beaker is ___ concentrated than the solution in the right. Increasing the concentration of the dye _________ the rate of color change in the material.

Factors Affecting Reaction Rates

5. _______- A substance that affects the reaction rate without being used up in the reaction.Catalysts are used so reactions can occur at

________ temperatures.

Catalysts are written _____ the arrow.

Energy is needed to start breaking the chemical bonds. This is called _________________. Catalysts lower that energy needed by providing a ________ on which the reacting particles can come together.

How a Catalyst Works

The graph shows how a catalyst lowers the amount of energy required for effective collisions between reacting particles.