Chapters 8, 17, and 18. Chapter 8 A chemical reaction is the process by which one or more substances...

Chapters 8, 17, and 18

Chapter 8

•A chemical reaction is the process by which one or more substances are changed into one or more different substances.

•In any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products.

What Is a Chemical Reaction?

Chapter 8 – Section 1: Describing Chemical Reactions

Visual Concept

• According to the law of conservation of mass, the total mass of reactants must equal the total mass of products for any given chemical reaction.

The Law of Conservation of Mass


Visual Concept

Signs that a chemical reaction is taking place:

1.Release of energy as heat and/or light.2.Production of a gas. 3.Formation of a precipitate.

- Precipitate - a solid that separates from a liquid solution.

4.Color change.

Indications of a Chemical Reaction


Visual Concept

• A chemical equation represents a chemical reaction using symbols and formulas.

Example:

Chemical Equations


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

1. The equation must represent known facts.

2. The equation must contain the correct formulas for the reactants and products.

3. The law of conservation of mass must be satisfied.

Rules for Writing Chemical Equations


•The first step in writing a chemical equation is to identify the facts.

•In a word equation the reactants and products are represented by words.

•A word equation is qualitative.Example: methane + oxygen carbon dioxide +

water

Word Equations


• The next step is to replace the names of the reactants and products with symbols and formulas.

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

Example: CH4(g) + O2(g) CO2(g) + H2O(g)

Formula Equations


• Oxygen gas (O2) is an example of an element that normally exists as a diatomic molecule. You need to memorize all seven:

Diatomic Molecules


Symbols used in Chemical Equations


Write word and formula equations for the reaction that occurs when solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper(II) nitrate.Solution:

Word Equation:

Formula Equation: (not balanced)

Word and Formula EquationsSample Problem


Cu(s)+ AgNO3(aq)→ Ag(s)

+ Cu(NO3)2(aq)

copper

+silver nitrate

silver

copper(II) nitrate

+→

• The final step in writing correct chemical equations is to make sure the law of conservation of mass is satisfied.– The numbers and types of atoms on both

sides of the equation must be the same – this is called balancing an equation.

– Equations are balanced by inserting coefficients - whole numbers that appear in front of formulas in a chemical equation.

Balancing Equations


Visual Concept

Balance the following equation: CH4(g) + O2(g) CO2(g) + H2O(g)Solution:•Start with the easiest element…carbon.

– Carbon is already balanced.•Next count the hydrogen atoms.

– Two more hydrogen atoms are needed on the right.•Finally, count oxygen atoms.

– There are 4 oxygens on the right side of the equation, but only two on the left.

– Add a coefficient 2 in front of the O2 on the left.

Balancing EquationsSample Problem A


22

Balance the following equation: Al4C3(s) + H2O(l) CH4(g) + Al(OH)3(s)Solution:•Let’s start with aluminum.

– Add a coefficient 4 to Al(OH)3 on the right.

•Next count the carbon atoms.

– Add a coefficient 3 to CH4 on the right.

•Balance the oxygen atoms.

– Add a 12 to the H2O on the left.

•Lastly, count the hydrogen atoms.– Hydrogen is already balanced.

Balancing EquationsSample Problem B


3 412

• There are 5 basic types of chemical reactions:1. Synthesis2. Decomposition3. Single-Displacement4. Double-Displacement5. Combustion

Types of Chemical Reactions

Chapter 8 – Section 2: Types of Chemical Reactions

Visual Concept

•In a synthesis reaction (also called a composition reaction) 2 or more substances combine to form a new compound.

•This type of reaction is represented by the following general equation:

A + X AX

Synthesis Reactions


• 2Mg(s) + O2(g) 2MgO(s)

• S8(s) + 8O2(g) 8SO2(g)

• 2H2(g) + O2(g) 2H2O(g)

• 2Na(s) + Cl2(g) 2NaCl(s)

• Mg(s) + F2(g) MgF2(s)

Synthesis - Examples


• In a decomposition reaction, a single compound breaks apart to form 2 or more simpler substances.

• Decomposition is the opposite of synthesis.

• This type of reaction is represented by the following general equation:

AX A + X

Decomposition Reactions


• 2H2O(l) 2H2(g) + O2(g)

• CaCO3(s) CaO(s) + CO2(g)

• H2CO3(aq) CO2(g) + H2O(l)

• 2HgO(s) 2Hg(l) + O2(g)

• Ca(OH)2(s) CaO(s) + H2O(g)

Decomposition - Examples


electricity

∆

∆

∆

• In a single-displacement reaction (also called single-replacement) one element replaces a similar element in a compound.

• They often take place in aqueous solution.

• This type of reaction is represented by the following general equation:

A + BX AX + B

Single-Displacement Reactions


• 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

• 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)

• Mg(s) + 2HCl(aq) H2(g) + MgCl2(aq)

• Cl2(g) + 2KBr(aq) 2KCl(aq) + Br2(l)

• F2(g) + 2NaCl(aq) 2NaF(aq) + Cl2(g)

Single Displacement - Examples


• In double-displacement reactions, the ionsof 2 compounds exchange places in an aqueous solution to form 2 new compounds.

• One of the compounds formed is usually either a precipitate, a gas, or water.

• Represented by the following general equation:

AX + BY AY + BX

Double-Displacement Reactions


•Formation of a Precipitate2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

•Formation of a GasFeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)

•Formation of WaterHCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Double Displacement - Examples


• In a combustion reaction, a fuel combines with oxygen, releasing a large amount of energy in the form of light and heat.

• Products of combustion reactions are always carbon dioxide and water vapor.

• Example: Combusion of propaneC3H8(g) + 5O2(g) 3CO2(g) +

4H2O(g)

Combustion Reactions


Classify each of the following reactions as a synthesis, decomposition, single-displacement, double-displacement, or combustion reaction.

a.N2(g) + 3H2(g) → 2NH3(g)

b.2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)

c.2NaNO3(s) → 2NaNO2(s) + O2(g)

d.2C6H14(l) + 19O2(g) → 12CO2(g) + 14H2O(l)

Types of ReactionsSample Problem


synthesis

single-displacement

decompositioncombustion

• The ability of an element to react is referred to as the element’s activity.

• The more easilyan element reactswith other substances, the greater its activity is.

Chemical Activity

Chapter 8 – Section 3: Activity Series of the Elements

LiAu

• An activity series is a list of elements organized by their chemical activity.• The most-active element is placed at the

top in the series.• It can replace each of the elements below

it in a single-displacement reaction.• Activity series can be used to predict

whether a chemical reaction will occur.• Activity series are based on experiment.

Activity Series


Activity Series (continued)


Use the activity series to predict whether or not there will be a reaction for the possibilities below. If a reaction will occur, write the products and balance the equation.a.Ni(s) + Pb(NO3)2(aq) → ____

b.MgCl2(aq) + Zn(s) → _____

c.Br2(l) + KI(aq) → _____

d.Cu(s) + HCl(aq) → _____

Activity SeriesSample Problem


Yes

Yes

No reaction

No reaction

Pb(s) + Ni(NO3)2(aq)

I2(l) + KBr(aq)

2 2

Chapters 17 & 18

• Collision Theory says that in order for reactions to occur between substances, particles must collide.

• For a collision to be effective, the particles must:1. Collide with sufficient energy.2. Have a favorable orientation.

Collision Theory

Chapter 17 – Section 1: The Reaction Process

•Energy is needed to overcome the repulsion forces between molecules and transform the reactants into an activated complex.

•Activation energy is the minimum energy required to get a reaction started.

Activation Energy

Chapter 17 – Section 1: The Reaction Process

• The rate of a chemical reaction depends on the number of collisions between particles.

• Rate-influencing factors are:–Nature of Reactants–Surface Area– Temperature–Concentration–Presence of Catalysts

Rate-Influencing Factors

Chapter 17 – Section 2: Reaction Rate

High Concentration Low ConcentrationVisual Concept

• A chemical reaction in which the products can react to re-form the reactants is called a reversible reaction.

• A reversible reaction is written using double arrows to show that the reaction is proceeding in both directions.

Example:

Reversible Reactions

Chapter 18 – Section 1: The Nature of Chemical Equilibrium

22HgO( ) 2Hg( ) O ( )s l + g

•A reversible reaction is in chemical equilibrium when the rate of its forward reaction equals the rate of its reverse reaction and the concentrations of its products and reactants remain unchanged.

•At equilibrium, both reactions continue, but there is no net change in the composition of the system.

Chemical Equilibrium

Chapter 18 – Section 1: The Nature of Chemical Equilibrium

Visual Concept

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Chapters 8, 17, and 18. Chapter 8 A chemical reaction is the process by which one or more substances...

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