Chapter 11

Chemical Reactions and Equations

Word Equations• Recall that word equations can

describe chemical reactions.

• Reactants are written to the left of the arrow and products are written to the right of the arrow.

• Recall how to name and write formulas from your flowchart.

• A skeleton equation is the formulas of the reactants and products without the amounts included.

Balancing Chemical Equations

• Skeleton equations do not require amounts but in order to use actual equations in chemistry, a balanced equation with amounts must be written.

Law of Conservation of Mass

• Chemical reactions must obey the Law of Conservation of Mass.

• Reactants must equal the products in amount and mass.

• A balanced chemical equation compares the amounts of reactants to products.

An Example….

• We need two wheels to make a toy car.

• They are sold only in twos.

• Each toy car has one car body (Cb) and 4 wheels are necessary. (W4)

• What would be our balanced chemical equation for the toy car?

Building a Toy Car

Building a Tricycle….• Again, we need one trike body (Tb)

but a tricycle has 3 wheels (W3) and the wheels only come in packages of two. (W2)

• How many orders of each tricycle should be make so there are no leftover parts?

• Write a balanced “chemical” equation.

Building Tricycle

Tips and Tricks…• If there is a polyatomic ion on

both sides of the equation, keep it together and balance it as one atom.

• Balance the more complicated compounds first.

• The elements that are by themselves should be balanced last.

• Sometimes it is helpful to create a chart below the equation to keep track of the numbers.

• If you have a word equation, write the skeleton equation first, then balance.

LET’S PRACTICE!• Balance the equations.

• AgNO3 + H2S Ag2S + HNO3

• Zn(OH)2 + H3PO4 Zn3(PO4)2 + H2O

• Iron(III) chloride + calcium hydroxide iron(III) hydroxide + calcium chloride

ANSWERS• Balance the equations.

• 2AgNO3 + H2S Ag2S + 2HNO3

• 3Zn(OH)2 + 2H3PO4 Zn3(PO4)2 + 6H2O

• 2FeCl3 + 3Ca(OH)2 2Fe(OH)3 + 3CaCl2

Vocabulary Cards

• Skeleton equation

• Reactants

• Products

• Law of Conservation of Mass

SUM IT UP!• Write the balanced

chemical equation for the following word equation.

• Hydrogen + sulfur hydrogen sulfide

Types of Chemical Reactions

• There are 5 general types of reactions.

• Occasionally, a reaction may fit equally into two categories.

• Identification is useful to help determine and predict the products.

Combination Reactions• It is also called a synthesis reaction.

• Two or more substances combine to create a single new substance.

• Mg + O2 MgO

• K + Cl2 KCl

• Balance these equations!

Decomposition Reactions• A single compound breaks down into

two or more simpler products.

• HgO Hg + O2

• H2O H2 + O2

• Balance these equations!

Single-Replacement Reaction• One element replaces a second element

in a compound.• Requires the activity series to determine

if the reaction will occur.• The element that is higher up on the

series will replace any lower elements.• A halogen (group 7) can replace any

other halogen providing that it is higher up on the periodic table.

• If a reaction doesn’t occur, write NR for no reaction.

Single-Replacement Reactions

• K + H2O KOH + H2

• Zn + Cu(NO3)2 Cu + Zn(NO3)2

• Br2 + NaI NaBr + I2

• Br2 + NaCl NR

• Balance these equations!

Double-Replacement Reactions• Sometimes when two solutions are

mixed, nothing happens.• Other times, the ions in the two solutions

react.• In these types of reactions, the two metal

(positive) cations switch places with each other.

• Occasionally, a precipitate will form or a gas will be generated.

• Sometimes, both products are aqueous so you won’t see anything different

Double-Replacement Reactions

• Na2S + Cd(NO3)2 CdS + NaNO3

• NaCN + H2SO4 HCN + Na2SO4

• Ca(OH)2 + HCl CaCl2 + H2O

• Balance these equations!

Combustion Reactions

• This is a chemical change that takes place when a compound (usually a hydrocarbon) reacts with oxygen (O2) and produces carbon dioxide, water and usually energy in the form of heat and/or light.

• C8H18 + O2 CO2 + H2O• When balancing, these numbers are

usually high.

Vocabulary Cards• Combination/Synthesis

Reaction• Decomposition Reaction• Single-Replacement Reaction• Double-Replacement

Reaction• Combustion Reaction

SUM IT UP

Write the balanced chemical reaction for the decomposition of aluminum oxide.

Combination or synthesis reaction

Single- Replacement Reaction

Decomposition Reaction

Double- Replacement Reaction

Combination or Synthesis Reaction

Single- Replacement Reaction

Double-Replacement Reaction

Decomposition Reaction

Double Replacement reaction

Reaction in Aqueous Solution• Your world is water-based.• Most reactions take place in water.• Most equations can show the reactions between

compounds but do not show how the compounds behave when dissolved in water.

• They actually separate into the various ions when in aqueous solution.

• You can use these ions to write a complete ionic equation.

• If the ion remains unchanged on both sides of the equation, it is called a spectator ion.

• The spectator ion doesn’t participate in the reaction directly and can be cancelled out.

• The resulting equation is called the net ionic equation.• Remember, the resulting equation must be balanced.

Net Ionic Equations

• A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge.

• Pb (s) + 2Ag+ (aq) 2Ag (s) + Pb +2 (aq)

• There are 2 Ag on both sides and +2 on both sides.

Solubility• Soluble means it can dissolve in

water or be aqueous.

• There are rules to determine if something is soluble or not.

• Page. 344 table 11.3 has the rules.

• If something is soluble write (aq).

• If it isn’t soluble or is insoluble, it is solid or (s).

• Check the table for the rules.

LET’S PRACTICE!

• Balance this equation.

• Ca+2 + OH- + H+ + PO4-3

Ca+2 + PO4-3 + H2O

Answers• Balance this equation.

• Ca+2 + 2OH- + 2H+ + PO4-3

Ca+2 + PO4-3 + 2H2O

• First balance the charges, then balance the numbers of the types of atoms.

• Both sides must have an equal charge.

LET’S PRACTICE!• Write the complete

and net ionic equations for:

• Sodium hydroxide (aq) and phosphoric acid (aq) makes calcium phosphate and water.

• Don’t forget to use your solubility rules.

Answers• Write the complete and net ionic equations

for:• Sodium hydroxide and phosphoric acid

makes calcium phosphate and water.• 3Ca(OH)2 (aq) + 2H3PO4 (aq) Ca3(PO4)2 (s) +

6H2O (l)

• 3Ca +2 + 6OH- + 6H+ + 2PO4-3 3Ca+2 +

2PO4-3 + 6H2O

• 6OH- + 6H+ 6H2O• Reduce• OH- + H+ H2O

Vocabulary Cards• Aqueous

• Spectator ion

• Complete ionic equations

• Net ionic equations

• Solubility

SCIENCE SWAG• Create your own

visual representation of the 5 types of chemical reactions we have studied.

• Put them on a poster.

• Due one week from today.

POST IT UP

I GOT THIS! I NEED HELP!

Write a balanced net ionic equation for Lead(II) nitrate (aq) reacting with sulfuric acid (aq). Hint: It’s a double replacement reaction.

Excessive Cuteness!