Reminders End of semester Fri. Jan 24 th (15 school days) Finals Jan Chp 6 E.C. (Passed out today/ due Mon. Jan 13 th )

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 Reactions 1) Synthesis 2) Decomposition 3) Single Replacement 4) Double Replacement 5) 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 2H 2 + O 2  2H 2 O

Breaking down the Notation of Chemical Equations 2H 2(g) + O 2(g)  2H 2 O (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) + O 2(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 with symbols and formulas. Fe + O 2  Fe 2 O 3 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 element on both sides of the equation. Fe + O 2  Fe 2 O 3

Step 4: Balancing Equations 4. Starting with elements that only occur in one substance on each side of the equation, make sure that each side of the equation 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 + O 2 ―› Fe 2 O 3

Let’s try: CH 4 +2O 2  CO 2 + 2H 2 O

Never change a subscript to balance an equation. ■ If you change the formula you are describing a different reaction. ■ H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula ■ 2 NaCl is okay, Na2Cl is not. !

Step 5: Check Your Work 5. Make sure that the equation is properly balanced. CH 4 + 2O 2  CO 2 + 2H 2 O

Balancing Equations: Examples ■ H 2 + O 2 → H 2 O ■ Co + O 2 → Co 2 O 3 ■ Pb(NO 3 ) 2 + K 2 S → PbS + KNO 3

Balance the following iron(II) chloride + sodium phosphate → sodium chloride + iron (II) phosphate FeCl 2 + Na 3 PO 4 → NaCl + Fe 3 (PO 4 ) 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 compounds AB = 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 + O 2 → 2CaO ■ carbon dioxide + water yields carbonic acid CO 2 + H 2 O → H 2 CO 3 ■ Notice: All equations show two (or more) reactants, but only one product. ■

II. Decomposition Reactions General form: AB → A + B (one reactant makes two or more products) AB = compound A, 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 oxygen 2H 2 O → 2H 2 + O 2 ■ marble (calcium carbonate) yields calcium oxide and carbon dioxide CaCO 3 → CaO + CO 2 ■ Notice: all equations show a single reactant decomposing into two (or more) products. ■

III. Single-Replacement Reactions General Form: A + BX → AX + B One element and one compound recombine (switch partners) AX, BX = ionic compounds A, B = Metals X = 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 + AgNO 3 → CuNO 3 + Ag ■ Notice: In the reaction, an copper combines with silver nitrate to create copper nitrate and silver

■ Zn + HCl → ZnCl 2 + H 2

IV. Double-Replacement Reactions General form: AX + BY → AY + BX (Positive ions in two compounds are exchanged) A,B = positive ions X,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 CaCO 3 + 2HCl → CaCl 2 + H 2 CO 3 ■ Notice: in this reaction, two ionic compounds exchange ions to form two new ionic compounds

IV. Double-Replacement Reactions General form: AX + BY → AY + BX (Positive ions in two compounds are exchanged) A,B = positive ions X,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 CaCO 3 + 2HCl → CaCl 2 + H 2 CO 3 ■ Notice: in this reaction, two ionic compounds exchange ions to form two new ionic compounds

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: C x H y + O 2 → H 2 O + CO 2 (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: CH 4 (methane) + O 2 → H 2 O + CO 2 ▪Gasohol reacts with oxygen: C 2 H 5 OH (ethanol) + O 2 → H 2 O + CO 2 ▪Notice: in both cases, water and carbon dioxide are the products.

1. Write the word equation 2. 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 equation 2. Write the balanced formula equation ■ Nitric acid reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate.