Chemical Reactions and Equations

Chapter 8

What does a chemical formula represent? The elements contained in a chemical

substance

Indicates the number of atoms of the element just to the right of the element symbol

a whole number that appears in front of a formula in a chemical equation.

What is a subscript? What does it indicate?

What is a coefficient?

Chemical Formulas

2 C8H18

indicates there are 8 Carbon atoms in

the molecule

indicates there are 18 hydrogen atoms

in the molecule

Coefficient means 2

molecules

Visualizing CompoundsExample: H2O

H atoms = ________

O atoms = ________

Model of H2O:

2

1

What is a diatomic element?An element with two atoms when it is by itself

H2 O2 F2 Br2 I2 N2 Cl2

Hydrogen Molecule Oxygen Molecule

DIATOMIC ELEMENTS

You can also mark them off on your periodic table as the SUPER SEVEN!

Chemical Reaction

When bonds are broken and new bonds are formed producing a new substance

Chemical Equation

Symbolizes or represents a chemical reaction

Reactants

Original substances in a chemical reaction

Products

Substances formed in a chemical reaction

REACTANTS yields PRODUCTS

H2 + O2 H2O

Igniting a mixture of hydrogen and oxygen will form water. The symbol equation is:

Reactants Product

How does a chemical reaction occur?

Atoms must collide for the reaction to occur

Atoms are rearranged in a chemical change- None are lost- None are gained

any reaction that gives off heat

Example:

2H2 (g) + O2 (g) 2H2O (l) + heat

Exothermic Reaction

Endothermic Reaction

any reaction in which heat is added

Example:

heat + 2HgO (s) 2Hg (l) + O2 (g)

Evidence of a Chemical Change

1. Color change (THAT YOU DID NOT CAUSE!!)

2. Temperature change3. Odor change4. Formation of a gas5. Formation of a precipitate

precipitate: insoluble solid that separates out of solution

Balancing Chemical Equations Notes

A Chemical Reaction

Potassium Iodide [KI] Lead Nitrate [Pb(NO3)2]

Final Product

Did a chemical change occur?How do you know?

Is matter conserved in this reaction?

According to the LAW OF CONSERVATION OF MATTER:

the total atoms of reactants must equal the total atoms of products[matter can’t be created or destroyed!]

When you have a chemical reaction, you must add coefficients to balance the

reaction!

Atom Inventory

__H2 + __O2 __H2O

Reactant Side

Product Side

Atom Type

Number of Atoms

Atom Type

Number of Atoms

H H

O O

2

2

2

1

UNBALANCED!

To balance an equation, coefficients CAN be added in front of products or reactants. DO NOT CHANGE SUBSCRIPTS!

New Atom Inventory__H2 + __O2 __H2O

Reactant Side

Product Side

Atom Type

Number of Atoms

Atom Type

Number of Atoms

H H

O O

4

2 2

2

2UNBALANCED!

New Atom Inventory__H2 + __O2 __H2O

Reactant Side

Product Side

Atom Type

Number of Atoms

Atom Type

Number of Atoms

H H

O O

2

4

2 2

2

4BALANCED!

Balancing Equations___ Mg + ___ N2 ---> ___ Mg3N2

 

___ H2S + ___ Cl2 ---> ___ S8 + ___ HCl

 

___ Al + ___ HCl ---> ___ AlCl3 + ___ H2

 

___ Fe2O3 + ___ CO ---> ___ Fe + ___ CO2

Classifying Chemical Reactions

• Two or more reactants combine to form ONE product.

(marriage)

example:

2Mg (s) + O2 (g) 2MgO (s)

A + X AX

Synthesis

• ONE reactant breaks down into smaller parts.

(divorce)

AX A + X

Decomposition

example:

2H2O (l) 2H2 (g) + O2 (g)

• A single element replaces an element that is part of a compound.

example:

2 Al(s) + 3 Fe(NO3)2(aq) 3 Fe(s) + 2 Al(NO3)3(aq)

A + BX B + AX Y + BX X + BY

Single Displacement

• Ions from two different compounds exchange places to form two new compounds.

(wife swap)

AX + BY AY + BX

2KI(aq) + Pb(NO3)2 (aq) PbI2 (s) + 2KNO3 (aq)

Double Displacement

• A compound (usually a hydrocarbon) reacts with oxygen, releasing carbon dioxide and water.

example: combustion of propane

C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g)

AB + O2 CO2 + H2O

Combustion

Activity Series

What is the activity series?

When elements are ranked in order of their relative reactivities

Activity Series of the Elements

1.Why is sodium not used for silverware?

It is highly reactive and reacts with water.

2. Why has so much gold 2. Why has so much gold jewelry survived from ancient jewelry survived from ancient civilizations?civilizations?

It is unreactive with oxygen or water and therefore does not readily break down.

3. Why is food canned in containers made from steel coated with a thin layer of tin?Steel makes a strong container and the tin lining does not react with the contents.

 

4. Why are cars painted?

To prevent the iron from rusting by being exposed to oxygen in air.

Writing Chemical Reactions Notes

word equation: equation in which the reactants and products in a chemical reaction are represented by words

a word equation is qualitative

example:

methane + oxygen carbon dioxide + water

Word Equations

formula equation: represents the reactants and products of a chemical reaction by their symbols or formulas

a formula equation is quantitative

example:

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

Formula Equations

Symbols in a Chemical Reaction

Writing Chemical Reactions

Steps to writing a reaction:1. Balance the equation.2. Fill in the phases of matter.3. Identify the reaction type.

Example 1Aluminum metal reacts with a solution of

hydrochloric acid to produce hydrogen gas and aluminum chloride solution.

Example 2Magnesium metal burns in oxygen gas to

produce solid magnesium oxide.

Example 3Hydrogen peroxide (H2O2) solution breaks down

to produce oxygen gas and liquid water in the presence of the catalyst “catalase”.

Example 4Iron (III) Chloride solution and sodium hydroxide

solution react to produce solid iron (III) hydroxide and sodium chloride solution.

Example 5A piece of zinc metal is placed in copper (II)

nitrate solution producing copper metal and zinc nitrate solution.

Example 6Copper (II) sulfate solution and sodium

hydroxide solution react to produce solid copper (II) hydroxide and sodium sulfate solution.