chemical reactions

Chemical Reactions

Three areas of focus Rearranging the

building blocks of chemistry (atoms/ions/ molecules/electrons)

Force & energy is what decides if the reaction occurs and how fast

Mathematics helps you keep an inventory of all the starting and ending materials

Objectives

Recognize Evidence of a chemical change. Represent chemical reactions with equations. Change word equations into formula equations. Given a description of a reaction, write a word and

formula equation. Balance chemical equations. Translate a formula equation into a sentence. Define and give a description of the major types of

chemical reactions. Classify reactions as one of five major types. Predict the products of simple reactions when given the

reactants. Understand, explain, and apply the activity series of the

elements.

Skills

  Memorize the diatomic elements Memorize the symbols used in chemical equations. Use the Activity Series for single replacement reactions Use the Solubility Chart for Double Replacement Reactions Know common gases Memorize substances that decompose

Carbonic acid, H2CO3 H2CO3 (aq) H2O+ CO2(g)  Sulfurous acid, H2SO3 H2SO3(aq) H2O + SO2(g)

Ammonium hydroxide, NH4OH NH4OH (aq H2O + NH3(g)

Chemical Reaction

The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

Also called a chemical change

We are making something new!

Equations show

the reactants which enter into a reaction.

the products which are formed by the reaction.

the relative amounts of each substance used and each substance produced.

Two important principles to remember

Every chemical compound has a formula which cannot be altered.

A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.

Evidence of a Chemical Reaction

Evidence of a Chemical Reaction

Production of a Gas Temperature Change Color Change Production of a Solid (precipitate) Production of Water or other unionized

substance

Representing Reactions

chemical equations – represent reactions

Reactants - starting Substances Products – ending substance

Symbols??

Some things to remember about writing equations

The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2

The sign,  →  , means "yields" and shows the direction of the action.

A small delta, ( ), above the arrow shows that heat has been added.

A double arrow,  ↔  , shows that the reaction is reversible and can go in both directions.

Word Equations

Using words in equation form to represent a chemical reaction

iron(s) + chlorine(g) iron(III) chloride(s)

Skeleton Equation

uses chemical formulas instead of words

Fe (s) + Cl2 (g) ----- FeCl3 (s)

Practice

Chemical Equation

In order to obey the Law of Conservation of Mass equations must be Balanced:

  Coefficients: number written in front of

a chemical formula to indicate the smallest number of particles involved in the reaction.

Steps for Balancing

Write skeleton equation. Change the coefficients to make the

number of atoms of each element equal on both sides of the equation. NEVER CHANGE A SUBSCRIPT!!!

Write the coefficients in the smallest ratio possible.

Check your work.

Helpful hints for balancing chemical equations

Start with “Big Formulas” C2H6O2

Save single elements for last O2 or Cu Balance hydrogens second to last Balance oxygens last Check for lowest ratio Do not change your subscripts Balance the polyatomic ions as one unit

(if it didn’t break apart) Perform a final check

If your equation doesn’t balance,

check your formulas!!

Classifying Chemical Reactions

  Five Types of Chemical

ReactionsSynthesis ReactionDecomposition ReactionSingle Replacement ReactionDouble replacement ReactionCombustion Reaction: oxygen

combines with a substance and produces heat and light

Synthesis Reaction: one product is formed from more than one simpler substances

A + B AB

Decomposition Reaction: One substance is broken down into one or more simpler substances: usually by the addition of energy

AB A + B

Single Replacement Reaction: atoms of one element replace another element in a compound

A + BC B + AC

Double replacement Reaction: involves the exchange of ions between two compounds

AB + CD AD + CB

Combustion Reaction: oxygen combines with a substance and produces heat and light

X + O2 H2O + CO2

Classify Each Reaction

Ca + O2 CaO Br + LiI LiBr + I Al + Fe(NO3)2 Al(NO3)3 + Fe MgO + HCl MgCl2 + H2O C4H10 + O2 CO2 + H2O NH4NO2 NH3 + H2O (NH4)3PO4 + Sr(OH)2 Sr3(PO4)2 + NH4OH H2SO4 + NaOH Na2SO4 + H2O Zn + AgNO3 Zn(NO3)2 + Ag CuNO3 + KCl KNO3 + CuCl

Predicting Products

Given the reactants predict what is formed Write formulas for reactants Identify the type of reaction Rearrange the atoms to write

formulas for products.

Single Replacement Reactions

Atoms of one element replace another element in a compound

A + BC B + AC

There are 3 Ways that a Single Replacement Reaction can occur.

1.) Metal replaces another metal in a compound

when zinc combines with iron (II) chloride the zinc replaces iron in the compound Z n + FeCl2 Fe + ZnCl2

2.) Metal replaces hydrogen in an acid or

water

3.) Nonmetal (halogen) replaces another nonmetal

(halogen)in a compound

Br2 + LiI LiBr + I2

Single Replacement Cartoon

How can we tell if a single replacement reaction will

happen? Use the activity series of the

elements If the free element is more active than

the element in the compound the reaction will happen

If the free element is below the element in the compound the reaction will not happen

The Activity Series

Another way to look at it

Bigger, stronger, orange shirted guy replaces white shirt guy in the dancing couple

Now we have new couple and new single guy

SINGLE REPLACEMENT LAB AND EXAMPLES FOR YOU TO PREDICT

THE PRODUCTS

http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/series/3perform.htm

Some Examples to Observe before lab

Double Replacement Reactions

two ionic compounds are mixed together in water

In water the ionic compounds split into anions and cations.

The cations have an opportunity to swap anions

A reaction occurs, if by swapping anions, a product is formed that cannot split apart into anions and cations

AB + CD AD + CB

AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)

Double Replacement: Will it occur?

A reaction occurs when a pair of ions comes together to produce a substance that removes ions from the solution. one of the following must occur

a precipitate: a solid produced during a reaction

a gas Water or other unionized substance a product that decomposes

http://www.wisc-online.com/objects/ViewObject.aspx?ID=gch1404

No Driving Force What happens when one of the three

possible products is not formed? Nothing All ions remain in solution (dissolved)

NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)

Without a driving force there is no change in the solution so we say No Reaction has taken place

Reactions that form a Precipitate

PbCl2(aq) + KI(aq) PbI2(s)+ KCl(aq)

Solubility Chart

Reactions that form a Gas

 Some double replacement reactions produce a gas. We observe this as bubbles or odors given off.  

Example: Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) +

H2S(g)

Products that Decompose

Some metathesis reactions do not give the product expected.

the expected product (H2CO3) decomposes to give a gaseous product (CO2) CaCO3 (s) + HCl (aq) CaCl2 (aq) + H2CO3

CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)

Products that DecomposeH2SO3 H2O + SO2

H2CO3 H2O + CO2

NH4OH H2O + NH3

Reactions that form Water

These water molecules increase the number of solvent molecules and we see no observable evidence

Usually accompanied by temperature change or

Neutralization which can be seen with an acid base indicator Example: H2SO4 + NaOH Na2SO4 +

H2O

Neutralization Reactions

Generally, when solutions of an acid and a base are combined, the products are a salt and water

HC2H3O2 (aq) + NaOH (aq) NaC2H3O2 (aq) + H2O (l)

Acid + Base Salt + Water

Molecular Equation

The molecular equation lists the reactants and products in their molecular form.

AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3

(aq)

Ionic Equation

In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.

This more accurately reflects the species that are found in the reaction mixture.

Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)

Net Ionic Equation

To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right.

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)

AgCl (s) + K+(aq) + NO3-(aq)

Net Ionic Equation

The only things left in the equation are those things that change (i.e., react) during the course of the reaction.

Ag+(aq) + Cl-(aq) AgCl (s)

Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions.

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)

AgCl (s) + K+(aq) + NO3-(aq)

Writing Net Ionic Equations

Write a balanced molecular equation. Dissociate all strong electrolytes (strong

acids, strong bases, and soluble ionic salts)

Cross out anything that remains unchanged from the left side to the right side of the equation.

Write the net ionic equation with the species that remain.

Combustion of Hydrocarbons

Hydrocarbon + oxygen CO2 + H2O Hydrocarbon: A compound of

hydrogen and carbon The phrase "To burn" means to

add oxygen unless told otherwise.

Complete Combustion: Hydrocarbon + oxygen CO2 + H2O Complete combustion means the

higher oxidation number is attained.

Incomplete Combustion: Hydrocarbon + oxygen CO + H2O Incomplete combustion means the

lower oxidation number is attained.

Combustion of Hydrocarbons

If oxygen is sufficient, the products are carbon dioxide and water vapor.

If oxygen is low, carbon monoxide will be produced.

automobile engine inside a closed garage or charcoal grill indoors.

Hydrocarbon (CxHy)  +  O2(g)  →    CO2(g)  +  H2O(g) EX. CH4(g)  +  2O2(g)  →    CO2(g)  +  2H2O(g) EX. 2C4H10(g)  +  13O2(g)  →    8CO2(g)  +  10H2O(g)

Combustion of Propane

C3H8 + O2 --> CO2 + H2O

propane 3 carbons = 3 carbon dioxide molecules

8 hydrogen atoms = four H2O molecules. balance the oxygen

Combustion of Acetylene

• This combustion of acetylene reaction is exothermic, and enough energy is released to melt metal. Used in welding.

Why So Hot??

Triple bond-multiple bonds-short bond length

Combustion Of Methane

Demo: Methane Snake Reaction CH4 + 2O2 CO2 + 2H2O

Synthesis Reactions

A + B AB Elem/Cmpd + Elem/Cmpd Compound One Product

Examples of Synthesis Reactions

Metal  +  oxygen  →   metal oxide 2Mg(s)  +  O2(g)  →    2MgO(s)

Nonmetal  +  oxygen  →    nonmetallic oxide C(s)  +  O2(g)  →    CO2(g)

Metal oxide  +  water  →    metallic hydroxide MgO(s)  +   H2O(l)  →    Mg(OH)2(s)

Nonmetallic oxide  +  water  →    acid CO2(g)  +  H2O(l)  →    ; H2CO3(aq)

Metal + nonmetal  →    salt 2 Na(s)  +  Cl2(g)  →    2NaCl(s)

A few nonmetals combine with each other 2P(s)  +  3Cl2(g)  →    2PCl3(g)

These two reactions must be remembered: N2(g)  +  3H2(g)  →    2NH3(g) NH3(g)  +  H2O(l)  →    NH4OH(aq)

Decomposition Reactions

AB A + B Compound Cmpd/Elem + Elem/Cmpd One Reactant

Examples of Decomposition Reactions AX  →   A  +  X

Metallic carbonates, when heated, form metallic oxides and CO2(g)

CaCO3(s)  →    CaO(s)  +  CO2(g)

Most metallic hydroxides, when heated, decompose into metallic oxides and water Ca(OH)2(s)  →    CaO(s)  +  H2O(g)

Metallic chlorates, when heated, decompose into metallic chlorides and oxygen 2KClO3(s)  →    2KCl(s)  +  3O2(g)

Some acids, when heated, decompose into nonmetallic oxides and water H2SO4  →    H2O(l)  +  SO3(g)

Some oxides, when heated, decompose 2HgO(s)  →    2Hg(l)  +  O2(g)

Some decomposition reactions are produced by electricity 2H2O(l)  →    2H2(g)  +  O2(g) 2NaCl(l)  →    2Na(s)  +  Cl2(g)

Summary

A + B AB (synthesis)AB A + B (decomposition)A + BC B + AC(single replacement)AB + CD AC + BD(double replacement)Hydrocarbon + oxygen CO2 + H2O(combustion/oxidation)