Chapter 8

What can chemical equations tell us?

How can we describe chemical reactions?

Before we start… In this chapter you MUST be able to name BOTH types of compounds- ionic and covalent. Be sure to brush up on naming as needed! You also MUST know which elements exist as diatomic molecules! ( BrINClHOF )

Section 1: Describing Chemical Reactions New substances are formed. Reactants = starting materials. Products = ending materials. Recall evidence of a chemical change/reaction: 1.Formation of a gas (bubbles/change in odor). 2.Formation of a precipitate (solid). 3.Change in energy: heat/light/sound given off (change in temperature). 4.Change in color. Chemical reactions are not always visible. Properties of substances change during chemical reactions.

Equations Word Equations: use names. Replace “and” with + Replace “yields”, “produces”, “forms” etc. with  Ex: methane and oxygen form carbon dioxide and water. methane + oxygen  carbon dioxide + water Chemical Equations: use formulas. Replace words with chemical formulas. Ex: methane + oxygen  carbon dioxide + water CH 4 + O 2  CO 2 + H 2 O

Information in an Equation Equations are like recipes – they give necessary information: Ingredients (substances involved) amounts Can also show physical states and conditions needed: SymbolMeaning (s), ( l ), (g) Substance in solid, liquid, or gas form (aq) Substance in aqueous form (dissolved in water) “Produces”, “yields”, etc. indicating results of reaction  Reversible reaction in which products can reform into reactants; final result is a mixture of products and reactants Reactants are heated; temperature is not specified Name or chemical formula of a catalyst, added to speed up a reaction Specific temperature or pressure needed for this reaction Δ heat Pd 500 o C2 atm

Practice Problems 1)Aqueous iron (II) chloride and lithium bromide react to form aqueous lithium chloride and iron (II) bromide. Write the word equation. 2)Solid calcium carbonate is heated and decomposes to form solid calcium oxide and carbon dioxide gas. Write the chemical equation. Include phases!

Section 1 Homework Honors: pg. 266 #2,3,9,11,13,17(a,b)

Why must chemical equations be balanced? How are chemical equations balanced?

Section 2: Balancing Chemical Reactions Law of Conservation of Mass! There must be the same number of each atom on both sides. Change coefficients NOT subscripts! Ex:

Steps for Balancing Equations 1.Write formulas for all chemicals. 2.Count atoms. Listing #s of each atom on both sides is helpful. Keep polyatomic ions as a group if they appear on both sides. 3.Insert coefficients. It often helps to balance H and O last. Try odd-even technique: place an even coefficient in front of a chemical that has an odd # of atoms- makes all atom #’s even. 4.Verify Results. Check #’s of atoms to make sure they’re equal!

Practice Problem #1 Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water. (1)Write equation: Fe 2 O 3 + H 2  Fe + H 2 O (2)Count # atoms on each side: (3) Balance # atoms on each side. (4) Double check your answer: Fe 2 O 3 + H 2  Fe + H 2 O Fe: O: O: H: H: Fe: O: O: H: H:

Practice Problem #2 The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write a balanced equation for this reaction.

Practice Problem #3- Using Fractions Sometimes it is helpful to use fractions as coefficients when balancing equations. This can help you to arrive at the correct coefficients more quickly. Ex: C 6 H 14 + O 2  CO 2 + H 2 O It is easy to first balance the C and H atoms: C 6 H 14 + O 2  6CO 2 + 7H 2 O Try using a fraction to balance the O atoms: C 6 H /2 O 2  6CO 2 + 7H 2 O Now multiply all coefficients by 2 to get whole #s. 2C 6 H O 2  6CO 2 + 7H 2 O

How can chemical equations be classified and how is this used to predict products?

Section 3: Classifying Chemical Reactions Classifying reactions allows us to better predict products. We will look at five types: combustion, synthesis, decomposition, single displacement, and double displacement. More than these five types exist. Some fall into more than 1 type. Some don’t fall into any type.

Combustion Generic formula: AB + O 2  CO 2 + H 2 O AB is a hydrocarbon (H and C bonded together). O may be present too. Always form CO 2 and H 2 O. Examples: CH 4 +O 2  CO 2 +H 2 O C 6 H 6 +O 2  CO 2 +H 2 O

Synthesis (Addition) Generic Formula: A + B  AB Can be element + element yielding one compound. Al + O 2  Al 2 O 3 Can be compound + compound yielding one compound. water + metal oxide  metal hydroxide: H 2 O + CaO  Ca(OH) 2 water + nonmetal oxide  acid: H 2 O + SO 3  H 2 SO 4 ammonia + acid  ammonium salt: NH 3 + HCl  NH 4 Cl

Decomposition Generic Formula: AB  A + B Can be a binary compound yielding two elements. NaCl  Na + Cl 2 Can be a ternary compound. metal chlorate  metal chloride and oxygen: KClO 3  KCl + O 2 metal carbonate  metal oxide and carbon dioxide: CuCO 3  CuO + CO 2 metal hydroxide yielding a metal oxide and water: Ca(OH) 2  CaO + H 2 O acid yielding nonmetal oxide + water: H 2 SO 4  SO 3 + H 2 O

Practice Name the type of reactions listed below and predict the product(s) for each: 1)Sr + O 2  2)C 3 H 6 + O 2  3)Al(OH) 3  4)CO 2 + H 2 O  SrO H 2 O + CO 2 Al 2 O 3 + H 2 O H 2 CO 3

Single Displacement When A is a metal: A + BC  AC + B If metal A is more reactive than metal B it displaces B’s spot in the compound: Cu + AgNO 3  Cu(NO 3 ) 2 + Ag If metal B is more reactive than metal A, no reaction occurs: Cu + HCl  no reaction (NR) METAL REACTIVITIES Li > Rb > K > Ba > Sr >Ca > Na > Mg > Al > Mn > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H 2 > Sb > Bi >Cu > Hg > Ag > Pt > Au metal nonmetal

Single Displacement continued When A is a nonmetal: A + BC  BA + C If nonmetal A is more reactive than nonmetal C it displaces C’s spot in the compound: Cl 2 + KBr  KCl + Br 2 If nonmetal C is more reactive than nonmetal A, no reaction occurs: Cl 2 + KF  no reaction (NR) NONMETAL REACTIVITIES F 2 > Cl 2 > Br 2 > I 2 metalnonmetal

Double Displacement Generic Formula: AB + CD  AD + CB When a compound plus a compound yields two new compounds. The metals ‘switch partners’ with the nonmetals. H 2 SO 4 + NaOH  H 2 O + Na 2 SO 4

More Practice Problems Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine. Magnesium is added to a solution of lead (II) nitrate. Will a reaction happen? If so, write the equation and balance it. Additional Practice: pg.279 #1-4 and pg.282 #1-3

Why are some parts of a reaction left out?

Section 4: Writing Net Ionic Equations Ionic compounds dissolve in water  ions separate and spread out.

Section 4: Writing Net Ionic Equations As long as a compound does not form a solid (precipitate), pure liquid, or gas, it will exist as ions in water, NOT as a compound. Ions that do not form a solid, pure liquid, or gas are called spectator ions (remain as ions in solution). Do not participate in the reaction. Use solubility rules to determine if a compound will remain as a solid in water (pg. 288). Write total ionic equation (all ions present). Cross out all spectators that appear on BOTH sides of the equation. Write final answer with remaining species- this is the net ionic equation.

Example Potassium iodide solution + lead (II) nitrate solution  ? Double displacement: KI (aq) + Pb(NO 3 ) 2 (aq)  ? KI (aq) + Pb(NO 3 ) 2 (aq)  KNO 3 (?) + PbI 2 (?) Use solubility rules or clues in question. 2 KI (aq) + Pb(NO 3 ) 2 (aq)  2 KNO 3 (aq) + PbI 2 (s) Total Ionic: 2 K + (aq) + 2 I - (aq) + Pb +2 (aq) + 2 NO 3 - (aq)  2 K + (aq) + 2 NO 3 - (aq) + PbI 2 (s) Net Ionic: 2 K + (aq) + 2 I - (aq) + Pb +2 (aq) + 2 NO 3 - (aq)  2 K + (aq) + 2 NO 3 - (aq) + PbI 2 (s) 2 I - (aq) + Pb +2 (aq)  PbI 2 (s) This is the reaction taking place.

Steps for Writing Net Ionic Equations 1.List what you know. Identify the type of reaction. Identify reactants (and products if provided). 2.Write a balanced chemical reaction. Use type to predict products (if not told what they are). Use solubility rules to predict states of matter. 3.Write total ionic equation. Separate ions (anything still in solution = aq). Do not separate any solids, liquids, or gases! 4.Find the net ionic equation. Cancel out any spectator ions and write remaining species. Double check that equation is balanced.

Practice Problem #1 Write the net ionic equation for the reaction that occurs when zinc is placed in a copper (II) sulfate solution. 1) Reaction type: 2) Balanced Equation: 3) Total Ionic Equation: 4) Net Ionic Equation: