Unit 8 - Chemical Reactions Student Outcomes: I can give 5 indications that a chemical reaction has occurred. I can use the activity series to predict.

Unit 8 - Chemical Reactions

Student Outcomes:

•I can give 5 indications that a chemical reaction has occurred. 

•I can use the activity series to predict the reactivity of chemical

reactions. 

•I can describe the five basic types of chemical reactions, including

single displacement/replacement, double displacement/replacement,

synthesis, decomposition, and combustion.

•I can explain how to identify the type of chemical reactions.

•I can balance chemical equations when given the reactants and

products. 

•I can predict products in chemical reactions.

Indications that a chemical Indications that a chemical reaction has occurred: reaction has occurred:

• Unexpected change in temperature (it gets hotter or colder but you did not intentionally add or remove heat)

• Unexpected color change• Unexpected odor change• Unexpected solid formation

(precipitate) or unexpected gas formation (bubbles)

Watch these chemical Watch these chemical reactions. Notice the evidence reactions. Notice the evidence of a chemical reaction taking of a chemical reaction taking

place.place.

https://www.youtube.com/watch?v=lJjfb2ydVzU

Types of ReactionsTypes of Reactions• There are five types of chemical

reactions we will talk about:1. Synthesis reactions2. Decomposition reactions3. Single displacement reactions4. Double displacement reactions5. Combustion reactions

• You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing ReactionsSteps to Writing ReactionsMain steps for doing reactions:

1. Identify the type of reaction2. Predict the product(s) using the type of

reaction as a model.3. Use subscripts to write the compounds.4. Use coefficients to balance the whole

reaction so that there are the same number of each element on each side of the reaction equation.

Don’t forget about the diatomic elements! (BrINClHOF)

If any of these are NOT part of a compound, they must be diatomic.

Bromine = Br2 Iodine = I2

Nitrogen = N2 Chlorine = Cl2

Hydrogen = H2 Oxygen = O2

Fluorine = F2

The word problem will simply state the name but you will write the diatomic in the reaction.

If it is part of a compound, do not add a suffix unless the criss-cross requires it.

Example: magnesium oxide = MgO

Indicators of state Indicators of state (these are written in (these are written in

italics and parenthesis after the reactants and products)italics and parenthesis after the reactants and products)

(s)(s) = solid state = solid state (l)(l) = liquid state = liquid state (g)(g) = gas state = gas state (aq) (aq) = dissolved in water (aqueous)= dissolved in water (aqueous)

Note: HgNote: Hg(l) (l) means liquid mercurymeans liquid mercury

HgHg+2+2(aq) (aq) or HgOor HgO(aq) (aq) means the means the mercury ions are dissolved in water.mercury ions are dissolved in water.

1. Synthesis reactions1. Synthesis reactions• Synthesis reactions occur when two

substances (usually elements) combine and form a compound. (Sometimes these are called “combination” or “addition” reactions.)

reactant + reactant 1 product• Basically: A + B AB

• Example: 2H2 + O2 2H2O

• Example: C + O2 CO2

Synthesis Reaction ExampleSynthesis Reaction Example

1. Predict the products. (Criss-Cross for subscripts.) 2. Balance the reactions. (Use only coefficients.)

• Sodium metal reacts with chlorine gas Na(s) + Cl2(g) • Solid Magnesium reacts with fluorine

gas Mg(s) + F2(g) • Aluminum metal reacts with fluorine

gas Al(s) + F2(g)

2Na(s) + Cl2(g) → 2NaCl

Mg(s) + F2(g) → MgF2

2Al(s) + 3F2(g) → 2AlF3

2. Decomposition Reactions2. Decomposition Reactions• Decomposition reactions occur

when a compound breaks up into the elements or in a few to simpler compounds

• 1 Reactant Product + Product • In general: AB A + B• Example: 2 H2O 2H2 + O2

• Example: 2 HgO 2Hg + O2

Decomposition Reaction:Decomposition Reaction:

Decomposition ExceptionsDecomposition Exceptions• Carbonates and chlorates are special

case decomposition reactions that do not go to the elements.• Carbonates (CO3

2-) decompose to carbon dioxide and a metal oxide

• Example: CaCO3 CO2 + CaO• Chlorates (ClO3

-) decompose to oxygen gas and a metal chloride

• Example: 2 Al(ClO3)3 2 AlCl3 + 9 O2

• There are other special cases, but we will not explore those in high school Chemistry.

1. Predict the products. (Criss-Cross for subscripts.) 2. Balance the reactions. (Use only coefficients.)

• Solid Lead (IV) oxide decomposes PbO2(s)

• Aluminum nitride decomposes AlN(s)

PbO2(s) → Pb(s) + O2(g)

2AlN(s) → 2Al(s) + N2(g)

PracticePracticeIdentify the type of reaction for each of

the following synthesis or decomposition reactions, and write the balanced equation:

N2(g) + O2(g)

BaCO3(s)

Co(s)+ S(s)

NI3(s)

(use Cobalt (III) in product)

Nitrogen monoxideN2(g) + O2(g) → 2NO (g) synthesis

2Co(s) + 3S(s) → Co2S3 synthesis

BaCO3(s) → CO2(g) + BaO

decomposition

2NI3(s) → N2(g) + 3I2(g)

decomposition

3. Single Replacement Reactions3. Single Replacement Reactions• Single Replacement Reactions occur when

one element replaces another in a compound.• A metal can replace a metal (+) OR

a nonmetal can replace a nonmetal (-).• element + compound element +

compound A + BC AC + B (if A is a metal) ORA + BC BA + C (if A is a nonmetal)

(remember the cation always goes first!)

When H2O splits into ions, it splits intoH+ and OH- (not H+ and O-2 !!)

Single Replacement ReactionSingle Replacement Reaction

Single Replacement ReactionsSingle Replacement Reactions

• Write and balance the following single replacement reaction equation:

• Zinc metal reacts with aqueous hydrochloric acid (HCl)

Zn(s) + HCl(aq) ZnCl2 + H2(g)

Note: Zinc (cation) replaces the hydrogen (cation) in the reaction

2

Single Replacement ReactionsSingle Replacement Reactions• Sodium chloride solid reacts with fluorine gas NaCl(s) + F2(g) NaF(s) + Cl2(g)

Note that fluorine (anion) replaces chlorine (anion) in the compound

• Aluminum metal reacts with aqueous copper (II) nitrate Al(s)+ Cu(NO3)2(aq) Cu(s) + Al(NO3)3

2 2

32 3 2

4. Double Replacement Reactions4. Double Replacement Reactions

• Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound

• Compound + compound compound+ compound

• AB + CD AD + CB

Double Replacement ReactionsDouble Replacement Reactions• Think about it like trading square dance

partners- cations are always paired with anions.

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

• Pretend Ag and Na are guys partnered with different girls in the dance. Ag switches partners with Na. NO3 is a polyatomic, so it acts like one partner. Remember the Ag and Na are still written first in the products (not NO3Na).

Double Replacement ReactionsDouble Replacement Reactions• Another example: K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s)

Pretend K and Ba are guys partnered with different girls in the dance. K switches partners with Ba. Both SO4 and NO3 are polyatomics, so they act like one partner each.

Notice the subscripts are not the same on each side because they depend on the criss-cross of the compound itself and are not carried over to the other side of the equation.

Predict the products by “trading partners.” Use subscripts to write the compounds.Use coefficients to balance the equation.1.HCl(aq) + AgNO3(aq)

2.CaCl2(aq) + Na3PO4(aq)

3.Pb(NO3)2(aq) + BaCl2(aq)

4.FeCl3(aq) + NaOH(aq)

5.H2SO4(aq) + NaOH(aq)

6.KOH(aq) + CuSO4(aq)

See next slide for answers.

Predict the products by “trading partners.” Use subscripts to write the compounds.Use coefficients to balance the equation.1.HCl(aq) + AgNO3(aq) HNO3 + AgCl

2.3 CaCl2(aq) + 2 Na3PO4(aq) Ca3(PO4)2 + 6 NaCl

3.Pb(NO3)2(aq) + BaCl2(aq) PbCl2 +Ba(NO3)2

4.FeCl3(aq) + 3 NaOH(aq) Fe(OH)3 + 3 NaCl

5.H2SO4(aq) + 2 NaOH(aq) 2 H2O + Na2SO4

6.2 KOH(aq) + CuSO4(aq) K2SO4 + Cu(OH)2

5. Combustion Reactions5. Combustion Reactions

• Combustion reactions occur when a hydrocarbon reacts with oxygen gas.

• This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)

Combustion ReactionsCombustion Reactions• In general:

CxHy + O2 CO2 + H2O• Products in combustion are

ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)

• Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Combustion Combustion ReactionsReactions

Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

CombustionCombustion

• Example• C5H12 + O2 CO2 + H2O

• Write the products and balance the following combustion reaction:• C10H22 + O2

5 68

20 CO2 + 22H2O

2 31

Mixed PracticeMixed Practice

• State the type, predict the products, and balance the following reactions:

1. BaCl2 + H2SO4

2. C6H12 + O2

3. Zn + CuSO4

4. Cs + Br2

5. FeCO3

BaSO4 + 2 HCl

6 CO2 + 6 H2O9ZnSO4 + Cu

2 CsBrFeO + CO2

2