Unit 10:Chemical Equations

Chapter Objectives

• 1. To learn to write chemical equations

• 2. To correctly interpret chemical equations

• 3. To balance chemical equations

Chapter Objectives

• 4. To classify chemical reactions• 5. To predict products of

chemical reactions• 6. To write ionic and net ionic

equations

Chemical Reactions

• In a chemical reaction, substances join together to form new substances

• The original substances present are called REACTANTS

• The new substances formed are called PRODUCTS

Discussion of Chemical Reactions

• The general form of an equation is:• Reactants Products• The is read as “yields” or “reacts

to produce”

Discussion of Chemical Reactions

• A + B C• Substance “A” and “B” react to

produce substance “C”

Additional Symbols in Chemical Reactions

•+ used to separate reactants or products

•(s) means chemical is in solid state

•(l) means chemical is in liquid state

Additional Symbols in Chemical Reactions

• (g) means chemical is in gas state• (aq) means chemical is dissolved

in water• *See Table 10-1 in book (page

278)

Other Symbols

means something is added to the reaction–Usually this is heat

• Pt means a catalyst (Pt) is added

Skeleton Equations

• Skeleton (Formula) Equation- the rough form of an equation

• It only shows the framework for the chemical reaction

Write Skeleton Equations

• Sodium metal reacts with Oxygen gas to form solid Sodium Oxide

• Solid sulfur reacts with Fluorine gas to form gaseous Sulfur Hexafluoride when heated

• Nitrogen reacts with Hydrogen to form Ammonia (NH3) gas. Heat is required.

Review-Write Skeleton Equations

• 1. Magnesium metal reacts with Chlorine to form solid Magnesium Chloride.

• 2. Aqueous Silver Nitrate reacts with aqueous Sodium Chloride to form solid Silver Chloride and aqueous sodium nitrate

Law of Conservation of Mass

• The Law of Conservation of Mass states that mass is neither created or destroyed in a chemical reaction

• Because of this Law, it is necessary to balance chemical equations

Balancing Chemical Equations

• In balanced chemical equations, each side of the equation has the same number of atoms of each element

•Coefficients are used to balance chemical equations

Question• What is the difference between a

coefficient and subscript?• Coefficients are written before the

formulas• Subscripts are part of the formula•Never use SUBSCRIPTS to

balance an equation!!

Rules for Balancing Equations

• 1. Determine the correct formulas for the reactants and products

• 2. Write the formulas for the reactants on the left side of the arrow. Write the formulas for the products on the right side of the arrow

Rules Continued

• 3. Count the number of atoms of each element present on both sides of the equation

• 4. Balance the elements one at a time by placing coefficients in front of the formula.

• 5. Check to make sure each atom is balanced

Additional Rules

• 6. Check to make sure that all coefficients are in the lowest possible ratio

• **If no coefficient is written, the coefficient is assumed to be “1”

Examples

• Balance the following

• H2 (g) + O2 (g) H2O (l)

• Na (s) + Br2 (g) NaBr (aq)

• AgNO3 (aq) + Cu(s) Cu(NO3)2 (aq) + Ag(s)

Classwork

•Complete Worksheet

Review-balance the following

•1. Fe + O2 Fe2O3

•2. Al2O3 + H2 Al + H2O

Quiz Review - Balance

•1. FeCl3 + NaOH Fe(OH)3 + NaCl

•2. CuCl2 + NaI CuI2 + NaCl

•3. H2O2 H2O + O2

QUIZ

•1) C6H6 + O2 CO2 + H2O

•2) Mg + O2 MgO

QUIZ REVIEW•1. Solid sulfur reacts with gaseous fluorine to produce aqueous sulfur hexafluoride

•2. Magnesium metal reacts with chlorine gas to make solid magnesium chloride

Additional Questions

• Pb(NO3)2 + 2 NaOH Pb(OH)2 + 2 NaNO3

• How many oxygen atoms are on the reactant side?

• How many oxygen atoms are in 2 NaNO3?

Balancing Equations -Determining Formulas

• To Balance Equations, you must remember how to write correct chemical formulas

Example

• Write the balanced equation for solid aluminum reacting with oxygen gas to form solid aluminum oxide

• **Remember that the diatomic elements (Mr. BrINClHOF) appear with a subscript of two when alone

Additional Examples

• 1. Carbon reacts with Chlorine to form Carbon Tetrachloride

• 2. Magnesium metal reacts with solid Zinc (II) Carbonate to form solid Magnesium Carbonate and Zinc metal

• 3. Nitrogen gas reacts with Hydrogen gas to form Ammonia (NH3) gas

Types of Reactions

• There are five general types of reactions:

• Synthesis• Decomposition• Single Displacement• Double Displacement• Combustion

Synthesis Reactions

• Synthesis reactions are also called combination reactions

• A synthesis reaction occurs when two substances combine to form a new compound

Synthesis Reaction Continued

• The general form of a synthesis reaction is:

• A + X AX• Substance “AX” is the only

substance formed

Examples of Synthesis Reactions

•2 Mg (s) + O2 (g) 2 MgO (s)

•Fe (s) + Cl2 (g) FeCl2 (s)

•U (s) + 3 F2 (g) UF6 (g)

Decomposition Reaction

• In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances

Decomposition Reactions Cont.

• General Form of Decomposition Reaction:

• AX A + X

Examples of Decomposition Reactions

• 2 HgO (s) 2 Hg (l) + O2 (g)

• Ca(OH)2 CaO (s) + H2O (g)

• H2SO4 (aq) SO3 (g) + H2O (l)

Write Correct Balance Equations

• 1. The synthesis of KCl• 2. The decomposition of

magnesium oxide• 3. The decomposition of hydrogen

peroxide (H2O2) into oxygen and water

Write Correct Balance Chemical Equations for the following reactions

• 1. The synthesis of barium fluoride

• 2. The decomposition of Mg(OH)2

into magnesium oxide and water• 3. The decomposition of water

Review-Write Balanced Equations

• 1. Gaseous hydrogen reacts with gaseous chlorine to form aqueous hydrogen chloride

• 2. Carbon monoxide gas reacts with gaseous oxygen to form solid carbon dioxide

Write balanced equations

• 1. The synthesis of Iron (III) oxide• 2. The decomposition of cobalt

(IV) oxide• 3. The decomposition of calcium

hydroxide into calcium oxide and water

Write Balanced Equations

•1) Na + Cl2

•2) HgCl2

•3) Fe(OH)3

Single Replacement Reaction

• In a single replacement reaction (also called a displacement reaction), an element reacts with a compound

•A + BX AX + B

Examples of Single Replacement Reactions

• Mg + Zn(NO3)2 Mg(NO3)2 + Zn

• Mg + 2 AgNO3 Mg(NO3)2 (aq) + 2 Ag

Rules for Single Replacement Reactions

•Not all single replacement reactions occur

•You can determine if a reaction will occur by knowing the activity series of metals (See Handout)

Rules for Single Replacement

• The activity series tell you if one metal can replace another metal in a reaction

• The Activity Series is ordered• Any metal that is above another

metal in the activity series WILL REPLACE the less reactive metal

Activity Series• Li• K• Ca• Na• Mg• Al• Zn

• Fe• Pb• H*• Cu• Hg• Ag

Predict if the following reactions will occur

• 1. Fe + H2O

• 2. Mg + LiNO3

• 3. Na + AgCl

Write balanced equations for the following reactions

• 1. Mg + O2

• 2. FeCl3

• 3. Fe + ZnO • 4. Br2 + MgI2

Review

• Predict the products and balance:

• 1) Mg + O2

• 2) HCl • 3) Na + H2SO4

• 4) Ag + ZnCl2

Double Displacement Reactions

• In a double displacement reaction, two compounds react

• The compounds swap elements with each other

Double Displacement Cont

• Compounds contain a positive and negative part

• In a double displacement, the positive parts swap places with each other as do the negative parts

Examples

• PbCl2 (s) + Li2SO4 (aq) PbSO4 (s) + 2 LiCl (aq)

• ZnBr2 (aq) + 2 AgNO3 (aq) Zn(NO3)2 (aq) + 2 AgBr (s)

Predict the Products of the following reactions and balance

• BaCl2 (aq) + KClO3 (aq)

• HCl (aq) + NaOH (aq) • RbBr (aq) + AgCl (aq)

Combustion Reactions

• In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2)

• The products are CO2 and H2O

Example

•2 C6H6 + 15 O212 CO2 + 6 H2O•*Combustion Reactions

commonly require large coefficients

Guided Practice• Write the balanced equation

for the following combustion reactions:

• a. C4H8

• b. C6H12O6

• c. C7H16

Independent Practice- Predict the products for the following reactions

• 1. Hf + N2 (Hf takes a +4 charge)

• 2. Mg + H2SO4

• 3. C2H6 + O2

• 4. Pb(NO3)2 + NaI

• 5. Fe + O2 (Fe takes a +3 charge)

Ionic Equations

• Most ionic compound dissociate (or break apart) when dissolved in water to form its component ions

• For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)

Soluble Vs. Precipitate

• Soluble means that the compound breaks down into its ions in water

• Ex) NaCl is soluble so it forms Na+ and Cl-

• Insoluble means that the compound doesn’t break down in water

Precipitate Reactions

• In double replacement reactions, often one of the product will be insoluble

• The insoluble product is referred to as a precipitate

Practice• Determine if soluble or insoluble:

• A) NaCl B) K2O

• C) Fe(NO3)3 D) AgCl

• E) BaS F) Cd(OH)2

• G) FeCl3 H) PbCO3

Ionic Equations Continued• To write a Complete Ionic

Equation:• Write the aqueous substances as

ions (leave any substances in gas, liquids, & solids alone)

• Example:

• AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

Writing Ionic Equations • 1. (NH4)2S (aq) + Cd(NO3)2

(aq) NH4NO3 (???) + CdS (???)

• 2. Zn(NO3)2 (aq) + (NH4)2S (aq) ZnS (???) + NH4NO3 (???)

Spectator Ions

• Spectator Ions-Ions that are not directly involved in a reaction

• Spectator ions show up on both sides of the equation

• Spectator Ions cancel out

NET Ionic Equations

• Net Ionic Equation-Indicate the particles that actually take part in a reaction

• The Net Ionic Equation does NOT include spectator ions

• Net Ionic Equations must be balanced according to atoms and charge

Write Net Ionic Equations

• 1. (NH4)2S (aq) + Cd(NO3)2 (aq)

• 2. Zn(NO3)2 (aq) + (NH4)2S (aq)