General Reactions

Dr. Ron RusayDr. Ron Rusay

General Chemical Reactions

Any chemical reaction can be described as a Any chemical reaction can be described as a molecular or atomic change. It produces one or molecular or atomic change. It produces one or more observable changes.more observable changes.

e.g. color change, gas bubbles, heat, etc.e.g. color change, gas bubbles, heat, etc. Reactions are generally described as Reactions are generally described as

Reactant(s) Product(s)Reactant(s) Product(s) The reaction is written as a chemical equation The reaction is written as a chemical equation

with chemical formulas:with chemical formulas:

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

1

The Reaction of Sodium & Chlorine

Chemical Equations

Chemical equations describe the change(s) in Chemical equations describe the change(s) in Reactant(s) to Product(s) including physical Reactant(s) to Product(s) including physical state(s).state(s).

Notations: Notations: (g), (l), (s), (aq)(g), (l), (s), (aq) 2 Na 2 Na (s)(s) + Cl + Cl22(g)(g) 2 NaCl 2 NaCl (s)(s) Others: Others:

arrows for gas ( ) and solid ( )arrows for gas ( ) and solid ( )

for heat, for reversibility (equilibrium)for heat, for reversibility (equilibrium)

1

Types of Chemical Reactions

Combination (Synthesis)Combination (Synthesis) DecompositionDecomposition Single DisplacementSingle Displacement Double DisplacementDouble Displacement CombustionCombustion Others: Precipitation, Oxidation-Others: Precipitation, Oxidation-

Reduction, NeutralizationReduction, Neutralization

General Chemical Reactions

Chemical Reactions

Combination (Synthesis)Combination (Synthesis) A + B CA + B C Example:Example:

• HH2 (g) 2 (g) + O + O2 (g) 2 (g) H H22O O (g) (g)

Balancing (Conservation of Atoms):2 H2 (g) + O2 (g) 2 H2O (g)

Synthesis of Water

An Unwanted Synthesis of WaterCombustion & the Hindenburg 1937

Chemical Reactions DecompositionDecomposition A B + CA B + C 2 NI2 NI3 (s)3 (s) N N2 (g)2 (g) + 3 I + 3 I2 (s)2 (s)

Decomposition

Another example:Another example:• Potassium chlorate (s) + heat Potassium chlorate (s) + heat

potassium chloride (s) + oxygen (g)potassium chloride (s) + oxygen (g)• Balanced equation: ?Balanced equation: ?

2 KClO3 (s) 2 KCl (s) + 3 O2 (g)

Ammonium nitrate, when heated, decomposes into nitrogen gas, oxygen gas, and water vapor. What is the sum of the coefficients in the balanced equation using smallest integer coefficients?

A) 3 B) 5 C) 7 D) 9

QUESTION

Ammonium nitrate, when heated, decomposes into nitrogen gas, oxygen gas, and water vapor. What is the sum of the coefficients in the balanced equation using smallest integer coefficients?

A) 3 B) 5 C) 7 D) 9

ANSWER

2 NH4NO3 (s) 2 N2 (g)+ 1 O2 (g) + 4 H2O (g)

Chemical Reactions

Single DisplacementSingle Displacement AB + C CB + AAB + C CB + A Example:Example:

• HCl HCl (aq) (aq) + Mg + Mg (s) (s) MgCl MgCl22 (aq) (aq) + H+ H22 (g)(g)

• Balanced Equation: ?Balanced Equation: ?

2 HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g)

Single Displacement(Oxidation / Reduction)

Write a balanced equation for the Write a balanced equation for the following reaction:following reaction:

Chemical Reactions

Double DisplacementDouble Displacement AB + CD AD + CBAB + CD AD + CB Example:Example:

• A solution of sodium phosphate reacts with A solution of sodium phosphate reacts with a solution of silver nitrate to produce a solution of silver nitrate to produce aqueous sodium nitrate and a precipitate of aqueous sodium nitrate and a precipitate of silver phosphate.silver phosphate.

• Balanced equation: ?Balanced equation: ?

Na3PO4 (aq) + 3 AgNO3 (aq) Ag3PO4 (s) + 3 NaNO3 (aq)

Chemical Equations

•Combustion:Combustion:

CC88HH18(l)18(l)+ O+ O2(g)2(g) CO CO2(g)2(g) + H + H22OO(l)(l)

Oxygen reacts with octane to produce carbon dioxide and water.Oxygen reacts with octane to produce carbon dioxide and water.

Reminder: the equation must balance:Reminder: the equation must balance:

2 C8H18(l)+ 25 O2(g) 16 CO2(g)+18 H2O(l) 16 CO2(g)+18 H2O(l)

QUESTION

ANSWER

2

D) 13

O should be balanced last since it contains only one type of element and balancing it will not cause an imbalance in another element.

2 C8H18 (l)+ 25 O2(g) 16 CO2(g)+18 H2O(l)

2 C4H10 (l)+ 13 O2(g) 8 CO2(g)+ 10 H2O(l)

Consider the molecular view of reactants converted to a product in the boxes shown below:

Which balanced equation best represents this reaction?

A) NO + Cl2 → Cl2NO B) 2 NO + Cl2 → 2 ClNO

C) N2 + O2 + Cl2 → 2 ClNO D) NO + Cl → ClNO

chlorine

nitrogen

oxygen

QUESTION

Consider the molecular view of reactants converted to a product in the boxes shown below:

Which balanced equation best represents this reaction?

A) NO + Cl2 → Cl2NO B) 2 NO + Cl2 → 2 ClNO

C) N2 + O2 + Cl2 → 2 ClNO D) NO + Cl → ClNO

chlorine

nitrogen

oxygen

ANSWER