Review-Molecular Formula

• Nicotine, a component of tobacco, has an empirical formula of C5H7N. The molar mass of nicotine is 162 g. What is its molecular formula?

• A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula.

Unit 10:Chemical Equations

Chapter Objectives

• 1. To learn to write chemical equations

• 2. To correctly interpret chemical 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.

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)

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

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

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)

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

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

• Precipitate Rules are on the EOC sheet

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)