Chemical Reactions

What is Chemical Change?

Standards• SC2 Students will relate how the Law of Conservation of Matter is

used to determine chemical composition in compounds and chemical reactions.

– a. Identify and balance the following types of chemical equations: – • Synthesis – • Decomposition – • Single Replacement – • Double Replacement – • Combustion – b. Experimentally determine indicators of a chemical reaction specifically

precipitation, gas evolution, water production, and changes in energy to the system.

• SC5. Students will understand that the rate at which a chemical reaction occurs can be affected by changing concentration, temperature, or pressure and the addition of a catalyst.

– a. Demonstrate the effects of changing concentration, temperature, and pressure on chemical reactions.

– b. Investigate the effects of a catalyst on chemical reactions and apply it to everyday examples.

• c. Explain the role of activation energy and degree of randomness in chemical reactions.

Level 1Nomenclature Review• Review these Websites if you are

feeling behind on naming and formula writing.

• Videos for remediation• Ionic vs covalent compounds;

– http://www.youtube.com/watch?v=PKA4CZwbZWU&feature=relmfu

• Naming Binary compounds; http://www.youtube.com/watch?v=vscoYh6m46M

• Formula writing for Transition Metals.– http://www.youtube.com/watch?v=CyFGooWJvGg&feature=relmfu

• Quiz yourself– http://www.gst-d2l.com/homework/NomenTut.html

Level 2 What is a Chemical Reaction?• What is a chemical reaction?• What is referred to as the Reactants? Products?• What are the Symbols associated with a chemical

reaction?• What are some indicators that reaction is occuring

?

• Wikipedia• Chem4Kids• Visionlearning• Windows to the Universe• Sparknotes

Level 3 Reaction Types

• What are the five main types of reactions?• What are the form of these reaction types?• What are some examples of each types of

reaction?

• Syvum.com• Chemistry.about.com• Fordhamprep.com• SCLinks

Level 4 Rates of Reactions

• Explain what is meant by “Rate” of a Reaction.

• How do you control the rate of a reaction? List some of the methods?

• What is a catalyst?

• www.purchon.com• Chemistry.about.com• Wikipedia.com

Chembalancer

• Get handout for chembalancer.

• Go to website.– http://www.dun.org/sulan/chembalancer/– Balance equations to get the answer to

the questions.

Chemical Reactions

• A process by which the atoms of one or more substances are rearranged to form different substances

Parts of a Reaction

• Reactants– The substances that combine together (or

react)

• Products– The new substances created or produced by

the rearrangement of atoms in the reactants

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Parts of a Reaction

• Symbols to know– (s) = solid– (g) = gas– (l) = liquid– (aq) solid dissolved in water– ↓ = precipitate forms– ↑ = gas forms

• Subscripts– Number of atoms

• Coefficients– Number of molecules of compound

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Parts of a Reaction

(Yield symbol)– Reads as“to produce” or “yields”

• + (on the reactant side)– Reads as “reacts with”

• + (on the products side)– Reads as“and”

HH22 (g)(g) + 2O + 2O22 (g)(g) 2H 2H22O O (l)(l)

Word & Skeleton Equations

• WORD EQUATIONS:– Use words and statements to indicate the reactants and

products of a reaction. – Example:

• iron(s) + chlorine(g) iron(III)chloride(s) • Read “Solid Iron and chlorine gas react to produce solid

iron (III) chloride”

• SKELETON EQUATIONS:– Uses chemical formulas rather than words to identify the

reactants and products of a chemical reaction. – Example:

• WORD EQUATION: iron(s) + chlorine(g) iron (III) chloride(s)

• SKELETON EQUATION: Fe(s) + Cl2(g) FeCl3(s)

Chemical Equation• Statement that uses chemical formulas to show

the identities and relative amounts of the substances involved in a chemical reaction– Example:

• WORD EQUATION: iron(s) + chlorine(g) iron(III)chloride(s)

• SKELETON EQUATION: Fe(s) + Cl2(g) FeCl3(s)

• CHEMICAL EQUATION: 2Fe(s) + 3Cl2(g) 2FeCl3(s)

2Fe + 3Cl2Fe + 3Cl22 2FeCl 2FeCl33

++

Indicators of a Chemical Reaction• Indications that a chemical reaction

has occurred are: – Permanent color change– Production of a new solid (precipitate)– Production of a new gas– Release of heat, light or sparks

Law of Conservation of Mass/Matter

• CONSERVATION OF MASS– Matter cannot be created nor destroyed… it can

only be rearranged!– In reactions

• The total mass of the reactants must equal the total mass of the products

– Due to the conservation of mass/matter…

ALL CHEMICAL EQUATIONS MUST BE BALANCED!!!

Balancing Reactions

• There are 4 rules for balancing chemical equations:

– Once you have written the chemical formulas for the compounds you…

1. CANNOT change SUBSCRIPTS2. CAN ONLY change COEFFICIENTS3. Use the LOWEST RATIOS4. If the same polyatomic ion is on both sides

of the equation, treat it like you would any other atom

Steps for Balancing Chemical Reactions

1. Write the skeleton equation

2. Make a product/reactant chart-- List the atoms on each side individually

-- Using subscripts & coefficients, determine how many of each atom exists

3. Balance the equation by changing coefficients

4. Reduce coefficients

EXAMPLES OF BALANCING…Na + INa + I22 NaI NaI

Na = 1Na = 1

I = 2I = 2Na = 1Na = 1

I = 1I = 1Does not equal, so… you must add coefficients…Does not equal, so… you must add coefficients…

22 22

Na = 1Na = 1

I = 2I = 2Na = 1Na = 1

I = 1I = 1

XX 22 XX 22

XX 22THE EQUATION IS NOW BALANCED!!THE EQUATION IS NOW BALANCED!!

EXAMPLES OF BALANCING…CHCH44 + O + O22 CO CO22 + H + H22OO

C = 1C = 1H = 4H = 4

C = 1C = 1H = 2H = 2

Does not equal, so… you must add coefficients…Does not equal, so… you must add coefficients…

22 22

THE EQUATION IS NOW BALANCED!!THE EQUATION IS NOW BALANCED!!

O = 2O = 2 O = 3O = 3

C = 1C = 1H = 4H = 4

C = 1C = 1H = 2H = 2

O = 2O = 2 O = 3O = 3XX 44XX 44XX 44

Balancing PracticeCaCO3 CaO + CO2

N2 + H2 NH3

CH4 + Cl2 CCl4 + HCl

NaCl + H2 + O2 NaOH + Cl2 + H2

Balancing PracticeKClO3 KCl + O2

FeCl3 + NaOH Fe(OH)3 + NaCl

Ag2O Ag + O2

K + MgBr2 KBr + Mg

Energy in Chemical Reactions• Endothermic Reactions

– More energy is absorbed to break original bonds than is released when new bonds are formed.

– Reaction feels cool.

• Exothermic Reactions– More energy is released when new bonds are formed when old

bonds are broken.– Reaction feels warm.– Most reaction are exothermic reactions.

• Catalysts– Substance that lowers the activation energy of a reaction in order to

speed up the reaction– Will NOT be used up in the process, just utilized to speed it up

Types of Chemical Reactions• Synthesis

– Two or more reactants combine to form one new product

– A + B AB

• Decomposition– When one reactant breaks

down into two or more products

– AB A + B

++

2Na + Cl2Na + Cl22 2NaCl 2NaCl

2H2H22O O 2H 2H22 + O + O22

+ +

Types of Chemical Reactions• Single Displacement

– When one ion replaces another of a like charge• AB + C AC + B

– Activity Series»Li»K»Ca»Na»Mg»Al»Zn

++ + +

2Li + 2H2Li + 2H22OO 2LiOH + H 2LiOH + H22

Types of Chemical Reactions• Double Displacement

– When the positive (+) ion of one compound replaces the positive (+) ion of another compound to form two new compounds

• AB + CD AD + CB

Ca(OH)Ca(OH)22 + 2HCl + 2HCl CaCl CaCl22 + 2H + 2H22OO

++ + +

Types of Chemical Reactions• Combustion

– An element or a compound reacts with oxygen, often producing energy in the form of heat and light.

• Ex. CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

+ + + +