Chapter 7 Balancing Chemical Equations

Chemical Reaction Describes chemical reaction. Describes chemical reaction. Chemical equation: reactants yield products Chemical equation: reactants yield products Catalyst = substance that speeds up a reaction without being used up.

Symbols Used (s) solid (s) solid (l) liquid (l) liquid (g) gas (g) gas (aq) aqueous (in water solution) (aq) aqueous (in water solution)  gas as a product  gas as a product  ppt. (precipitate)  ppt. (precipitate)  means with heat  means with heat Ptmeans with Platinum catalyst Ptmeans with Platinum catalyst

Balancing Chemical Equations Balanced equations have: the same # of atoms of each element on each side of the equation. Balanced equations have: the same # of atoms of each element on each side of the equation. Law of Conservation of Mass – atoms can neither be created nor destroyed, simply rearranged. Law of Conservation of Mass – atoms can neither be created nor destroyed, simply rearranged.

Rules for Balancing Equations Get the correct formulas for reactants and products. Get the correct formulas for reactants and products. Write reactants on left, products on right and use plus signs and arrows when needed. Write reactants on left, products on right and use plus signs and arrows when needed. Count the # of atoms of each element in reactants and products.(Polyatomic ions on both sides count as one.) Count the # of atoms of each element in reactants and products.(Polyatomic ions on both sides count as one.) Balance # of each element using coefficients. Balance # of each element using coefficients. –Coefficient – whole # in front of a formula.

Rules for Balancing Equations Check each element to make sure equation is balanced. Check each element to make sure equation is balanced. Make sure all coefficients are in the lowest whole number ratio. Make sure all coefficients are in the lowest whole number ratio. Do not change subscripts!!!

Diatomic Molecules Diatomic Molecules- a molecule made up two atoms of the same element. They are only diatomic when they are alone. -There are 7 naturally occurring diatomic molecules. H O N Cl Br I F

5 Types of Reactions - 1 Combination Reaction – elements combine to form a compound. A + B AB

Examples of Combination Reactions 1. 2 Na + Cl 2 2 NaCl 2. Cu + S Cu 2 S 2 3. SO 3 + H 2 O H 2 SO 4 4. CaO + H 2 O Ca(OH) 2 5. Mg + O 2 MgO 2 2

5 Types of Reactions - 2 Decomposition Reaction – elements break down into its element. AB A + B AB A + B

Examples of Decomposition Reactions 1. 2 NaCl 2 Na + Cl 2 2. H 2 O H 2 + O HgOHg +O Challenge: Copper I Chloride Decomposes 2CuCl 2Cu + Cl 2

5 Types of Reactions - 3 Single Replacement Reaction – one element replaces another element in a compound. AB + C A + CB AB + C A + CBor AB + D AD + B AB + D AD + B

Reactivity Series of Metals and Non-Metals The single metallic element will only replace the metal in a compound if it is more reactive. The single metallic element will only replace the metal in a compound if it is more reactive. A chart is used to determine if the lone metal is more reactive. If not, no reaction occurs. A chart is used to determine if the lone metal is more reactive. If not, no reaction occurs. The single non-metallic element will only replace the non-metal in a compound if it is more reactive. The higher up in the group the non-metal is, the more reactive it is. The single non-metallic element will only replace the non-metal in a compound if it is more reactive. The higher up in the group the non-metal is, the more reactive it is.

Examples of Single Replacement Reactions 1. Zn + H 2 SO 4 ZnSO 4 + H 2 2. K + HOH KOH + H 2 3. Cl 2 + NaBr NaCl + Br 2 22

5 Types of Reactions - 4 Double Replacement Reaction – two compounds react and exchange positive ions to form two new compounds. AB + CD AD + CB AB + CD AD + CB

Examples of Double Replacement Reactions 1. NaOH + H 2 SO 4 Na 2 SO 4 + HOH 2. BaCl 2 + K 2 CO 3 BaCO 3 + KCl 3. FeS + HCl H 2 S + FeCl

5 Types of Reactions - 5 Combustion Reaction – oxygen reacts with a compound composed of C and H. C x H y + O 2 CO 2 + H 2 0 C x H y + O 2 CO 2 + H 2 0 Also called Burning (exothermic) The products are always CO 2 and H 2 O.

Examples of Combustion Reactions 1. C 6 H 6 + O 2 CO 2 + H 2 O 2. CH 3 OH + O 2 CO 2 + H 2 O 367½ 21½ CH 3 OH + O 2 CO 2 + H 2 O C 6 H 6 + O 2 CO 2 + H 2 O

Special Decomposition Reactions: 1 Decomposition of a Carbonate: Decomposition of a Carbonate: XCO 3 XO + CO 2 ex. Na 2 CO 3 Na 2 O + CO 2

Special Decomposition Reactions: 2 Decomposition of a Hydroxide: Decomposition of a Hydroxide: XOH XO + H 2 O ex. 2NaOH Na 2 O + H 2 O

Special Decomposition Reactions: 3 Decomposition of a Chlorate: Decomposition of a Chlorate: XClO 3 XCl + O 2 XClO 3 XCl + O 2 ex. NaClO 3 NaCl + O 2

Special Decomposition Reactions: 4 Special single Replacement Reaction: Special single Replacement Reaction: »Group IA or IIA metal and H 2 O X + HOH XOH + H 2 ex. 2Na + 2HOH 2NaOH + H 2

How to ID types of reactions. Combination Reactions – given 2 items that form 1 new compound. Decomposition Reactions – given a single compound that breaks into parts. Single Replacement – given a single element plus a single compound, forms a new compound a a different element. Double Replacement – given two compounds (+’s or –’s change places). Combustion Reaction – given CH compound with Oxygen, always forms water and carbon dioxide.