Indicators of chemical reactions

• Emission of light or heat

• Formation of a gas

• Formation of a precipitate

• Color change

• Emission of odor
 All chemical reactions:

have two parts:

• Reactants - the substances you start
with
• Products- the substances you end up
with
The reactants turn into the products.
• Reactants → Products
 Describing chemical reaction
• The way atoms are joined is changed
• Atoms aren’t created or destroyed.

Can be described several ways

• In a sentence
Copper reacts with chlorine to form copper (II)
chloride.
• In a word equation
Copper + chlorine → copper (II) chloride
• In a chemical equation

Cu(s) + Cl2(g) → CuCl2(aq)

 Symbols used in equations
• (s) after the formula –solid Cu(s)
• (g) after the formula –gas H2 (g)
• (l) after the formula -liquid H2O(l)
• (aq) after the formula - dissolved in
water, an aqueous solution. CaCl2 (aq)
• ↑ used after a product indicates a gas
(same as (g)) O2 ↑
• ↓ used after a product indicates a solid
(same as (s)) CaCO3 ↓
 Symbols used in equations

• indicates a reversible reaction.

• shows that heat is
supplied to the reaction.
• , or is used to
indicate a catalyst used supplied, in this case,
platinum.
• , indicates a
pressure other than STP
Summary of Symbols
 What is a catalyst?

• A substance that speeds up a reaction

without being changed by the
reaction.
• Enzymes are biological or protein
catalysts.
 Reaction Energy
• All chemical reactions are accompanied by a change in
energy.
• Exothermic - reactions that release energy to their
surroundings (usually in the form of heat)
-ΔH (enthalpy) is negative ;energy leaving system

• Endothermic - reactions that need to absorb heat

from their surroundings to proceed.
+ΔH (enthalpy) is positive ;energy coming into
the system
 Reaction Energy
• Spontaneous Reactions - Reactions that proceed
immediately when two substances are mixed together.
Not all reactions proceed spontaneously.

• Activation Energy – the amount of energy that is

required to start a chemical reaction.
•Once activation energy is reached the reaction
continues until you run out of material to react.
 Formula Equation

• Uses formulas and symbols to

describe a reaction

• doesn’t indicate how many.

• All chemical equations are sentences

that describe reactions.
 Diatomic elements
• There are 8 elements that never want to
be alone.
• They form diatomic molecules.
• H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , and At2
• The –ogens and the –ines
• 1 + 7 pattern on the periodic table
 Convert this to an equation
Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form
iron (II) chloride and hydrogen
sulfide gas.

Fe2S3 (s) + HCl(g) → FeCl2 (s) + H2S(g)

 Convert this to an equation
Nitric acid dissolved in water reacts
with solid sodium carbonate to form
liquid water and carbon dioxide gas
and sodium nitrate dissolved in water.

HNO3 (aq) + Na2CO3 (s) → H2O(l) + CO2 (g) + NaNO3 (aq)

 TRY THESE: Convert the following descriptions:

1. Sulfuric acid + Iron (III) Hydroxide → Iron (III )sulfate + water

H2SO4 + Fe(OH)3 → Fe2(SO4)3 + H2O

2. Sodium iodide + Bromine → sodium Bromide + iodine

NaI + Br2 → NaBr + I2

3. Sulfur Dioxide + Oxygen → Sulfur trioxide

SO2 + O2 → SO3
4. Zinc + Nickel Chloride → Zinc Chloride + Nickel

Zn + NiCl → Zn Cl2 + Ni

5. Hydrogen Sulfide + Silver Nitrate → Silver Sulfide + Nitric acid

H2S + AgNO3 → Ag2S + HNO3

 TRY : The other way

Fe(s) + O2(g) → Fe2O3(s)

Solid iron reacts with oxygen gas to

form solid iron oxide (rust).
 A silver spoon tarnishes. The solid silver reacts
with sulfur in the air to make solid silver
sulfide, the black material we call tarnish.

Ag (s) + H2S (g) + O2 (g) → Ag2S (s) + H2O

 Balancing Equations

2 H2(g) + ___ O2(g) ---> ___

___ 2 H2O(l)
•What Happened to the Other Oxygen Atom?
•This equation is not balanced!
•Two hydrogen atoms from a hydrogen molecule (H2) combines
with one of the oxygen atoms from an oxygen molecule (O2) to
form H2O. Then, the remaining oxygen atom combines with
two more hydrogen atoms (from another H2 molecule) to make
a second H2O molecule.
ALUMINUM
BROMINE
 Translate Equation

Aluminum metal reacts with liquid bromine

to form solid aluminum bromide

___ 3 Br2(l) →___

2 Al(s) + ___ 2 AlBr3(s)
 TRY THESE: Translate some more!
1. Calcium Fluoride and Sulfuric acid make Calcium Sulfate and
Hydrofluoric acid.

2. Calcium Carbonate will come apart when you heat it to leave

Calcium Oxide and Carbon Dioxide.

3. Ammonia gas when it is pressed into water will make Ammonium

Hydroxide.

4. Aluminum Sulfate and Calcium Hydroxide become Aluminum

Hydroxide and Calcium Sulfate.

5. Copper metal and Silver Nitrate react to form Silver metal and
Copper (II) Nitrate.

6. Sodium metal and Chlorine react to make Sodium Chloride.

TYPES OF CHEMICAL REACTIONS
 Types of Reactions

• There are millions of reactions.

• Can’t remember them all
• Fall into several categories.
• We will learn 6 types.
• We will be able to predict the products.
• For some we will be able to predict
whether they will happen at all.
• We will recognize them by the reactants
 Combination or Synthesis Reactions
• 2 elements, or compounds combine to make
one compound.
• A + B → AB
• Na (s) + Cl2 (g) → NaCl (s)
• Ca (s)
+O2 (g) → CaO (s)
• SO
3
+ H 2
(s)
O (l)
→ H 2
SO 4 (s)
• We can predict the products if they are two
elements.
• Mg (s) + N2 (g) → Mg3N2 (s)
A simulation of the reaction:
2H2 + O2 → 2H2O
 EXAMPLES OF SYNTHESIS REACTIONS

1. An element + 1 element → a compound of 2 elements

2Cu (s)
+ O2 (g) 2CuO (s)

2.Nonmetal oxide + water → oxyacid

SO2 (g) + H2O (l) → H2SO3 (aq)

3.Metal + oxygen metal oxide

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

4. Metal oxide + water → metal hydroxide

CaO(s) + H2O(l) → Ca(OH)2 (aq)

5.Nonmetal + Oxygen → nonmetal oxide

S(s) + O2 (g) → SO2 (g)

6. Metal oxide + nonmetal oxide → salt

MgO (s) + SO3 (g) → MgSO4 (s)
 Analysis or Decomposition
Reactions
• decompose = fall apart
• one compound (reactant) falls apart into two
or more elements or compounds.
• Usually requires energy
• AB → A + B
• NaCl Na + Cl2
• CaCO CaO + CO2
3
 Decomposition Reactions
• Can predict the products if it is a binary
compound
• Made up of only two elements
• Falls apart into its elements

• H O
2
H2 (g) + O2 (g)
• HgO Hg (s) + O2 (g)
 Types of Decomposition Reactions:

1. When OXIDE is heated, OXYGEN is given off as

one of the products.

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

2. Some CARBONATES, when heated decompose to yield

CARBON DIOXIDE.

CaCO3 (s) CaO (s) + CO2 (g)

Continuation….

3. Bicarbonates, when heated decompose to yield

CARBON DIOXIDE, WATER and A CARBONATE SALT.

2NaHCO3 (s) CO2(g) + H2O (l) + Na2CO3 (s)

4. Hydrates when heated readily decompose. Water is

driven off, leaving the anhydrous salt.

CuSO4 • 5H2O CuSO4 + 5H2O

 Decomposition Reactions
• If the compound has more than two
elements you must be given one of the
products
• The other product will be from the
missing pieces
• NiCO CO2 (g) + Ni (s)
3 (aq)
• H CO (aq) → H2 (g) + CO2 (g)
2 3
 Single Replacement
• Also referred to as single displacement
• One element replaces another
• Reactants must be an element and a
compound.
• Products will be a different element and a
different compound.
• A + BC → AC + B
• 2Na + SrCl2 → Sr + 2NaCl

• F + LiCl → LiF + Cl
2 2
 Single Replacement
• We can tell whether a reaction will happen
• Some are more active than other
• More active replaces less active
ACTIVITY SERIES OF METALS
• Decreasing Activity
• Li Pb
• K (H)
• Ca Cu
• Mg Hg
• Al Ag
• Zn Au
• Fe
Activity Series of Halogens

• F2
• Cl2
• Br2
• I2
 Consider the following reactions:

1. Zn + FeSO4 (aq) ZnSO4 (aq) + Fe

(s) → (s)

2. 2 Na (s) + 2 H2O(l) 2 NaOH (aq) + H2 (g)

→

3. Mg + H2SO4 (aq) MgSO4 (aq) + H2 (g)

(s) →
 Double Replacement
• Two things replace each other.
• Reactants must be two ionic compounds or
acids.
• Usually in aqueous solution
AB + CD → AD + CB

ZnS + 2HCl → ZnCl + H2S

AgNO3 + NaCl → AgCl + NaNO3

 Combustion

• A reaction in which a compound

(often carbon) reacts with oxygen
• CH4 + O2 → CO2 + H2O
• C3H8 + O2 → CO2 + H2O
• C6H12O6 + O2 → CO2 + H2O
• The charcoal used in a grill is basically
carbon. The carbon reacts with oxygen to
yield carbon dioxide. The chemical equation
for this reaction is C + O2 🡪 CO2
 Acid/Base Reaction
• An acid and a base react to form a salt
and water.
• Always in aqueous solution
• Acid (H+) + Base (OH-) → Salt + H2O

NaOH + HCl → NaCl + H2O

NH4OH + H2SO4 → (NH4)2SO4 +

H2O
How to recognize which type
• Look at the reactants
● Element(E), Compound(C)
• E+E Synthesis
• C Decomposition Redox
• E+C Single replacement
• C+C Double replacement
• Acid + Base Acid/Base reaction

• Look at the Products

Combustion
• CO2 + H2O
 Examples

•H + O →
Synthesis
2 2
•H O → Decomposition
2
•AgNO + NaCl → Double replacement
3
•Zn + H SO → Single replacement
2 4
•HgO → Decomposition
•KBr +Cl → Single replacement
2
•Mg(OH) + H SO → Double replacement
2 2 3
 Examples

•HNO3 + KOH → Acid/Base

•CaPO4 → Decomposition
•AgBr + Cl2 → Single replacement
•Zn + O → Synthesis
2
•HgO + Pb→ Single replacement
•HBr + NH4OH → Acid/Base

•Cu(OH) + KClO → Double replacement

2 3
 Summary
An equation:
• Describes a reaction
• Must be balanced because to follow Law of
Conservation of Energy
• Can only be balanced by changing the
coefficients.
• Has special symbols to indicate state, and if
catalyst or energy is required.
• Can describe 5 different types of reactions.