Unit 10: Chemical Equations

1. To learn to write chemical equations Chapter Objectives 1. To learn to write chemical equations 2. To correctly interpret chemical equations 3. To balance chemical equations

4. To classify chemical reactions Chapter Objectives 4. To classify chemical reactions 5. To predict products of chemical reactions 6. To write ionic and net ionic equations

The original substances present are called REACTANTS 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)

 means something is added to the reaction Usually this is heat Other Symbols  means something is added to the reaction Usually this is heat Pt means a catalyst (Pt) is added

Skeleton (Formula) Equation- the rough form of an equation 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 Begin 3rd 1-4-2002, 4th, & 5th, 7th

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 Begin 1st, 3rd, 5th, & 7th 11-29-99

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 Begin 3rd 1/18/02, 4th, & 5th

5. Check to make sure each atom is balanced 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

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

Na (s) + Br2 (g)  NaBr (aq) 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) Begin 3rd 1-21-02, 4th, 5th

Classwork Complete Worksheet

Review-balance the following 1. Fe + O2  Fe2O3 2. Al2O3 + H2  Al + H2O

Begin 4th & 5th Periods 1. FeCl3 + NaOH  Fe(OH)3 + NaCl Quiz Review - Balance 1. FeCl3 + NaOH  Fe(OH)3 + NaCl 2. CuCl2 + NaI  CuI2 + NaCl 3. H2O2  H2O + O2 Begin 4th & 5th Periods

QUIZ 1) C6H6 + O2  CO2 + H2O 2) Mg + O2  MgO

1. Solid sulfur reacts with gaseous fluorine to produce aqueous sulfur hexafluoride 2. Magnesium metal reacts with chlorine gas to make solid magnesium chloride QUIZ REVIEW

Begin 4th & 5th Periods Pb(NO3)2 + 2 NaOH  Pb(OH)2 + 2 NaNO3 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? Begin 4th & 5th Periods

Balancing Equations - Determining Formulas To Balance Equations, you must remember how to write correct chemical formulas Begin 4th & 5th Periods

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 Begin 3rd 1/24/01

There are five general types of reactions: Synthesis Decomposition Single Displacement Double Displacement Combustion Begin 3rd 1-9-2001, 4th, 5th, & 7th

Synthesis reactions are also called combination reactions A synthesis reaction occurs when two substances combine to form a new compound Begin 5th 1-10-01

Synthesis Reaction Continued The general form of a synthesis reaction is: A + X  AX Substance “AX” is the only substance formed Begin 4th 1/25/02

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) Begin 4th 1-10-11 & 5th

Decomposition Reaction In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances Begin 1st 1-10-01

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 Begin 3rd 1-10-2001

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 Begin 3rd 1-10-2001

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 Begin 4rd 1/25/01

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 Begin 4th & 5th 1/27/02

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) Begin 3rd 1/28/02

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 1-11-2001 Begin 3rd

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 

Begin 4th, 1/29/02 Predict the products and balance: 1) Mg + O2  Review Predict the products and balance: 1) Mg + O2  2) HCl  3) Na + H2SO4  4) Ag + ZnCl2  Begin 4th, 1/29/02

Double Displacement Reactions In a double displacement reaction, two compounds react The compounds swap elements with each other Begin 4th, 1/29/02

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

PbCl2 (s) + Li2SO4 (aq)  PbSO4 (s) + 2 LiCl (aq) 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)  Begin 3rd 1-12-01, 7th

The products are CO2 and H2O Combustion Reactions In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2) The products are CO2 and H2O Begin 1st 1-29-02

*Combustion Reactions commonly require large coefficients Example 2 C6H6 + 15 O212 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 Begin 3rd 1-16-01, 4th, 7th

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) Begin 3rd, 1-17-01, 4th, 5th

For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq) 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) Begin 3rd 12-7-99, 5th, 7th

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 Begin 1st 12-7-99

The Net Ionic Equation does NOT include spectator ions 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) 