CHEMICAL REACTIONS

Reactants: Zn + I2 Product: Zn I2

Unit 2 – Chemical Reactions

The unit 2 exam will cover material

from multiple chapters. You are

responsible for the following from your

text on exam 2. Chapter Sections

3 3.1, 3.2

4 4.1- 4.4

20 20.1- 20.2

There are three ways we write

chemical equations

1. Molecular Equations

2. Full Ionic Equations

3. Net Ionic Equations

On the national exam, you will see both Molecular and Net Ionic Equations. From now on, you should pay close attention to which form of chemical equation is requested in each problem.

© 2012 Pearson Education, Inc.

Law of Conservation of Mass

“We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.”

--Antoine Lavoisier, 1789

Anatomy of a Chemical Equation

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

• Reactants appear on the left side of the equation.

• Products appear on the right side of the equation.

Anatomy of a Chemical Equation

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

The states of the reactants and products are

written in parentheses to the right of each

compound.

Anatomy of a Chemical Equation

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

Coefficients are inserted to balance the

equation.

Subscripts and Coefficients Give Different

Information

• Subscripts tell the number of atoms of each

element in a molecule.

• Coefficients tell the number of molecules.

Molecular Equations • Gives overall reaction in terms of

the parent species, but NOT necessarily the actual forms of reactants & products undergoing a chemical change. (misleading)

• Must be balanced

• Should include the correct physical states

Today, we will focus on…

Because of the principle of the conservation of matter,

an equation must be balanced.

It must have the same number of atoms of the same kind on both sides.

Molecular Equations

Lavoisier, 1788

Balancing Equations

____C3H8(g) + _____ O2(g) → _____CO2(g) + _____ H2O(g)

____B4H10(g) + _____ O2(g) →

___ B2O3(g) + _____ H2O(g)

Representing Physical States for

Reactants and Products

Physical states can be identified for all

types of matter:

1. Atoms and Elements

2. Ionic Compounds (ions)

3. Molecules

Physical States at Room Temperature

•All metal atoms are solids except Hg

and Ga.

Physical States

at Room

Temperature

Con’t.

•Non-metals

atoms (including

di- and

polyatomic

elements) and can

be (s), (l) or (g).

Physical States at

Room Temperature

Con’t.

•All natural ionic

compounds are solids

NaCl Crystal

Lattice

• Solutions are defined as

homogeneous mixtures of

two or more pure

substances.

• The solvent is present in

greatest abundance.

• All other substances are

solutes.

Physical States at Room Temperature

Con’t.

•Ionic compounds can sometimes dissociate

into solution

Dissociation

• When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them.

• This process is called dissociation.

Water Solubility of Ionic Compounds

•Ionic compounds, commonly called

salts, have varying solubilities. See

Table 4.1 on pg. 121.

•Solubility refers the the amount of a

substance that can be dissolved in a

given quantity of solvent at a given

temperature.

•If the attractions between solvent

particles for the solute particles is

stronger than the attractions between

solute particles, the solute particles can

go into solution and are said to be

soluble.

•If the attractions between solute

particles are too great, the substance is

said to insoluble.

Water Solubility of Ionic Compounds

Handout

Solubility of Salts in Water

1. Most nitrate salts are soluble

2. Most salts containing the alkali

metal ions and the ammonium

ion are soluble

3. Most chloride, bromide, and

iodide salts are soluble, EXCEPT

of salts containing the ions of

silver, lead (ll), and mercury (l)

Solubility of Salts in Water

4. Most sulfate salts are soluble,

EXCEPT with ions of barium,

lead (Il), mercury (ll), and calcium

5. Most hydroxide salts are only

slightly soluble. The important

soluble hydroxides are NaOH

and KOH. Barium, strontium,

and calcium hydroxides are

marginally soluble

6. Most sulfide, carbonate, chromate,

and phosphate salts are only slightly

soluble

Memorize Patterns On Solubility

Handout

Solubility of Salts in Water

Physical States at Room Temperature

Con’t.

•Molecules can be (s), (l) or (g).

Physical States at Room Temperature

Con’t.

•Molecules can sometimes be dissolved or ionized

into solution

Some molecules dissolve

in water but do not

conduct electricity.

They are called

nonelectrolytes.

Examples include:

sugar

ethanol

ethylene glycol

Dissolution

• An electrolyte is a substance that dissociates

into ions when dissolved in water.

• A nonelectrolyte may dissolve in water, but it

does not dissociate into ions when it does so.

Electrolytes and Nonelectrolytes

Soluble ionic

compounds tend

to be electrolytes.

Electrolytes and Nonelectrolytes

Molecular

compounds tend

to be

nonelectrolytes,

except for acids

and bases.

ACIDS & BASES

HCl(aq) ---> H+(aq) + Cl-(aq)

•Acids and bases are molecules that are

ionized by the loss or addition of hydrogen

nuclei in the presence of a solvent

•Acid:

•Base:

NaOH(aq) → Na+(aq) + OH-(aq)

Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

Movie

STRONG ACIDS

• Some strong acids are:

HCl hydrochloric

H2SO4 sulfuric

HClO4 perchloric

HNO3 nitric

• There are seven strong acids total. A strong acid is a strong electrolyte; therefore, it completely ionizes in solution

HNO3

Weak Acids Acetic acid ionizes

only to a small

extent, so it is a

weak electrolyte.

CH3CO2H(aq) →

CH3CO2-(aq) + H+

(aq)

Electrolytes

• A strong electrolyte dissociates completely when

dissolved in water.

• A weak electrolyte only dissociates partially when

dissolved in water.

Monoprotic acid: HCl

HCl(aq) + NaOH(aq) →

H2O(l) + NaCl(aq)

H+ + Cl- + Na+ + OH- →

H2O + Na+ + Cl-

H+ + OH- → H2O

diprotic acid: H2SO4

H2SO4(aq) + 2NaOH(aq) →

2H2O(l) + Na2SO4(aq)

H+ + OH- → H2O

polyprotic acid: H3PO4

H3PO4(aq) + 3NaOH(aq) →

3H2O(l) + Na3PO4(aq)

H3PO4 + 3 OH- →

3 H2O + PO43-

Ammonia, NH3

An Important Weak Base

Know the strong

acids & bases!

Strong Electrolytes Are…

• Strong acids

• Strong bases

• Soluble ionic salts

Some Simple Patterns of Chemical Reactions

Based on:

• What atoms do in a

chemical reaction.

• What type of

products are

formed

Synthesis

A.K.A. (combination)

A + B → AB

elements compounds

• Any atom or group of atoms

combine to form a more

complex compound

Decomposition

AB → A + B

elements

compound and/or simpler compounds

• A compound is broken down into simpler substances

A + BX → AX + B

• a more reactive element replaces a less reactive element in a compound (involves ions)

Predicted using the ‘Activity Series’

(get out your activity series)

Single Displacement

Double Displacement AX(aq) + BY (aq) → AY (?) + BX (?)

•Exchange of ions between two or more

compounds

• Precipitation Reactions

• Neutralization Reactions

• Double Displacement Reactions

Combustion Substance + O2 → Oxide of Elements

hydrocarbon + O2 CO2+ H2O

• Oxides are formed from each element in

the compound being combusted.

A hydrocarbon in combustion reactions refer to

only carbon, hydrogen and oxygen containing

compounds