Reminders

• End of semester Fri. Jan 24th (15 school days)

• Finals Jan 22-24

• Chp 6 E.C. (Passed out today/ due Mon. Jan 13th)

One cool thing you did over break…

Today

• Chp 9 Learning Targets

• Unexpected Changes Lab

• Introduction to Chp 9

• Handout E.C. assignment

Chapter 9(Last one for the semester!)

Chemical Reactions and Writing Equations

1/6/14 Learning Targets

• Describe the characteristics of a chemical reaction.

• Explain how a chemical equation describes what happens in a chemical reaction.

Important Terms:

• Chemical Change (Reaction)- a process in which pure substance(s) are converted into different pure substance(s)

• Conservation of Matter- in chemical and physical reactions, matter is neither created nor destroyed

Examples

Combustion of Ethanol

Oxidation of Iron

Precipitation of Silver

Formation of Coral Reefs (from Calcium Carbonate)

How do we describe/represent what happens in a chemical reaction?

Reactants- substances which are present before a chemical reaction

Products- substances which are present after a chemical reaction

What causes chemical reactions?

• What do we know about the importance of valence electrons?

Chemical reactions provide atoms the opportunity to achieve a full set of valence electrons and

become more stable (more energetically favorable)

Since some elements/molecules are already stable, energy sometimes has to be supplied to initiate a

chemical reaction (think back to the flame test lab) (strike a match!)

Reminders

• End of semester Jan 24 (14 school days)

• Finals Jan 22-24

1/7/14 Learning Targets

• Explain how a balanced chemical equation illustrates the law of conservation of matter.

• Understand the five general types of reactions and how to balance them.

Types of Chemical Reactions1) Synthesis2) Decomposition3) Single Replacement4) Double Replacement5) Combustion

By knowing the type of reaction that is occurring, you can predict the products that will be formed.

Chemical Equations- How we describe what is happening

Using Words-Hydrogen reacts with oxygen to form (or yield)

water

Using Formulas and Symbols

2H2 + O2 2H2O

Breaking down the Notation of Chemical Equations

2H2(g) + O2(g) 2H2O(l)

Describing the physical state of each substance

■Solid (s)■Liquid (l)■Gas (g)■Aqueous (aq)means dissolved in water

Coefficient

• Like in math, the coefficient is the number placed in front of a formula. This number indicates the quantity of each molecule or atom in the reaction.

• Ex. 2Ca(s) + O2(g) 2CaO(g)

Symbols used in Chemical Equations

• Double arrow indicates a reversible reaction

• Shows that heat is supplied to the reaction

• Used to indicate a catalyst is supplied, in this case, platinum.

All of these are special conditions

Balancing Chemical Equations

• Since the conservation of mass says matter is neither created nor destroyed, we have to make sure our equation agrees

• # reactant atoms must = # product atoms

Step 1: Balancing Equations

• Write the word equation that describes the reaction.

iron reacts with oxygen to yield iron oxide

Or

Iron + Oxygen Iron Oxide

Step 2: Balancing Equations

2. Replace the words in the equation withsymbols and formulas.

Fe + O2 Fe2O3

Do we have the same numbers of each element on both sides of arrow?

Does this follow the law of conservation of matter?

Step 3: Balancing Equations

3. Count the # of atoms of each elementon both sides of the equation.

Fe + O2 Fe2O3

Step 4: Balancing Equations

4. Starting with elements that only occurin one substance on each side of theequation, make sure that each side of theequation has an equal # of that element.

Proceed with all elements.

Remember that changing the # of one element may alter elements that have already been balanced.

Fe + O2 ―› Fe2O3

Let’s try:

CH4 +2O2 CO2 + 2H2O

• Never change a subscript to balance an equation.■ If you change the formula you are describing a

different reaction.

■H2O is a different compound than H2O2

• Never put a coefficient in the middle of a formula■ 2 NaCl is okay, Na2Cl is not.

!

Step 5: Check Your Work5. Make sure that the equation is properly

balanced.

CH4 + 2O2 CO2 + 2H2O

Balancing Equations: Examples

■ H2 + O2 → H2O

■ Co + O2 → Co2O3

■ Pb(NO3)2 + K2S → PbS + KNO3

Balance the following

iron(II) chloride + sodium phosphate → sodium chloride + iron (II) phosphate

FeCl2 + Na3PO4 → NaCl + Fe3(PO4)2

Today

■ Look at 3 different types of reactions.

■ Begin “Single-Replacement Lab” set-up.

Five General Types of Chemical Reactions

• Direct Combination (Synthesis)• Decomposition• Single-Replacement• Double-Replacement• Combustion

By knowing the type of reaction that is occurring, you can predict the products that will be formed.

I. Direct Combination Reactions (also called synthesis reactions).

General form: A + B → AB (two reactants make a single product)

A, B = elements or compoundsAB = compound consisting of A

and B

■ This is the only type of chemical reaction in which there is a single product formed. This single product is always more complex than the reactants.

Examples of Synthesis Reactions

■calcium + oxygen yields calcium oxide

2Ca + O2 → 2CaO

■ carbon dioxide + water yields carbonic acidCO2 + H2O → H2CO3

■ Notice: All equations show two (or more) reactants, but only one product.

■ http://www.ric.edu/ptiskus/reactions/Index.htm

II. Decomposition Reactions

General form: AB → A + B (one reactant makes two or more

products)

AB = compoundA, B = elements or simpler

compounds

▪ This is the only type of chemical reaction in which there is a single reactant. This single reactant is always more complex than the products.

Decomposition Reactions: Examples

■ water yields hydrogen and oxygen2H2O → 2H2 + O2

■ marble (calcium carbonate) yields calcium oxide and carbon dioxideCaCO3 → CaO + CO2

■ Notice: all equations show a single reactant decomposing into two (or more) products.

■ http://www.ric.edu/ptiskus/reactions/Index.htm

III. Single-Replacement Reactions

General Form: A + BX → AX + BOne element and one compound

recombine (switch partners)AX, BX = ionic compounds

A, B = MetalsX = ion that switches partners

*Metal ‘A’ must be more reactive than ‘B’ for this to occur

Single-Replacement Examples

■ Copper metal and silver nitrate:

Cu + AgNO3 → CuNO3 + Ag

■ Notice: In the reaction, an copper combines with silver nitrate to create copper nitrate and silver

■ Zn + HCl → ZnCl2 + H2

IV. Double-Replacement Reactions

General form: AX + BY → AY + BX(Positive ions in two compounds are exchanged)

A,B = positive ionsX,Y = negative ions

■ This is the only type of chemical reaction with two compounds as reactants and two compounds as products.

Double Replacement Examples

■ calcium carbonate and hydrochloric acid yield calcium chloride and carbonic acid

CaCO3 + 2HCl → CaCl2 + H2CO3

■Notice: in this reaction, two ionic compounds exchange ions to form two new ionic compounds

www.ric.edu/ptiskus/reactions/Index.htm

IV. Double-Replacement Reactions

General form: AX + BY → AY + BX(Positive ions in two compounds are exchanged)

A,B = positive ionsX,Y = negative ions

■ This is the only type of chemical reaction with two compounds as reactants and two compounds as products.

Double Replacement Examples

■ calcium carbonate and hydrochloric acid yield calcium chloride and carbonic acid

CaCO3 + 2HCl → CaCl2 + H2CO3

■Notice: in this reaction, two ionic compounds exchange ions to form two new ionic compounds

www.ric.edu/ptiskus/reactions/Index.htm

Rules of Double-Replacement Reactions

■ Reactants must be dissolved in water (releasing the ions).

■ Will occur if one of the products :• is a molecule (covalent), • a precipitate (solid comes out of

solution), or• an insoluble gas.

V. Combustion Reactions

General Form: CxHy + O2 → H2O + CO2

(hydrocarbon and oxygen react to form carbon dioxide and water)

■ This is the only type of chemical reaction where something reacts with oxygen and forms carbon dioxide and water

Combustion Examples

▪ Methane reacts with oxygen:CH4 (methane) + O2 → H2O + CO2

▪ Gasohol reacts with oxygen:C2H5OH (ethanol) + O2 → H2O + CO2

▪ Notice: in both cases, water and carbon dioxide are the products.

www.ric.edu/ptiskus/reactions/Index.htm

1. Write the word equation2. Write the balanced formula equation■ Solid iron (III) sulfide reacts with

gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.

1. Write the word equation2. Write the balanced formula equation

■ Nitric acid reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate.