Chapter 8: Chemical Equations and Reactions

8.1 Describing Chemical Reactions a process in which 1 or more substances are converted into a NEW substance with different chemical and physical properties Chemical reaction- a process in which 1 or more substances are converted into a NEW substance with different chemical and physical properties. Is an uncooked egg and a cooked egg exactly the same??

In a chemical reaction there are 2 types of substances: reactants and products. – The substance that enters into the reaction is the REACTANT. – The new substance(s) produced by the reactions is/are the PRODUCT(s). H 2 + Cl 2 2 HCl Ex. H 2 + Cl 2 → 2 HCl Reactants Products describes what is happening in a chemical reaction. IDs the reactants and products. Chemical equation- describes what is happening in a chemical reaction. IDs the reactants and products.

Indications of a Chemical Reaction 1.Evolution of Light 2.Production of a Gas

3. Formation of a Precipitate 4. Color Change

Characteristics of Chemical Equations 1.The equation must represent known facts 2.The equation must contain the correct formulas for the reactants and products. 3.The law of Conservation of mass must be satisfied. COEFFICIENTSwhole #s written before the formula of reactant or products. – In order to balance the equation… you must use COEFFICIENTS- whole #s written before the formula of reactant or products.

Word Equations Simplest type of equation; give names of reactants and products. +→+ Aluminum + Hydrochloric acid → Aluminum chloride + Hydrogen +reacts with On the REACTANTs side the + reads “reacts with” +and On the PRODUCTs side the + reads “and” → yieldsforms produces The → reads “yields”, “forms” or “produces”

Formula Equations More common than word equations; uses formulas instead of names. AKA- chemical equation. – Al + HCl → AlCl 3 + H 2 You would still “read” the equation the same as the word equation Ex Reactants Products + → + 2CH 4 + 4O 2 → 2CO 2 + 4H 2 O reacts with to formand You read the equation as Methane reacts with oxygen to form carbon dioxide and water.

Writing Complete Chemical Equations Indicate the states of matter of the reactants and products. –Use (g) for gaseous substances. –Use (s) for solids. –Use (l) for liquids. –Use (aq) for species in solution in water. Write the state of matter immediately following the formula of the substance it describes. Additional symbols table p.246

Significance of a Chemical Equation 1.The coefficients for a chemical rxn indicate relative, not absolute, amounts of reactants and products. H 2 + Cl 2 2 HCl H 2 + Cl 2 → 2 HCl Shows the smallest whole # ratio of the molecules: 1 molecule H 2, 1 molecule Cl 2, 2 molecules HCl

2. The relative masses of the reactants and products of a chemical reaction can be determined from the reaction's coefficients. 3. The reverse reaction for a chemical equation has the same relative amounts of substance as the forward reaction.

Balancing Chemical Reactions 1.ID names of reactants & products, write word equation. 2.Convert word equation to formula equation. 3.Balance formula equation according to the law of conservation of mass.  Balance the different types of atoms one at a time.  1 st balance atoms of elements that appear once on each side of equation  Balance polyatomic ions that appear on both sides of equation as a unit  Balance H & O atoms last. 4. Count atoms to be sure the equation is balanced.

Practice Ca + O 2 → CaO –22 –2Ca + O 2 → 2CaO Mg + N 2 → Mg 3 N 2 –3 –3Mg + N 2 → Mg 3 N 2 CH 4 + O 2 → CO 2 + H 2 O 22 –CH 4 + 2O 2 → CO 2 + 2H 2 O FeCl 2 + Na 3 PO 4 → NaCl + Fe 3 (PO 4 ) 2 –326 –3FeCl 2 + 2Na 3 PO 4 → 6NaCl + Fe 3 (PO 4 ) 2

8.2 Types of Chemical Rxns There are 4 general types of Chemical rxns: Direct Combination, Decomposition, Single-replacement and Double-replacement. Each type is distinguished by how the products are formed.

Direct Combination aka Synthesis Rxn – Synthesis rxns. combine substances. – General Synthesis (combination) rxn formula A + B → AB ex. 2Na + Cl 2 → 2NaCl 2Mg+O 2 → 2MgO 2C(s) +2O 2 (g) → 2CO 2 (g) CaO+H 2 O → Ca(OH) 2 It’s always 2 substances that react to form 1 new substance.

Decomposition Rxn – Decomposition rxns - Break substances apart. – General rxn formula: AB → A + B Ex. 2H 2 O → 2H 2 + O 2 H 2 CO 3 → H 2 O + CO 2 2KClO 3 → 2KCl + 3O 2 It’s always 1 substance breaks down to form 2 new substances.

Single- Replacement rxns Single Replacement rxn - a rxn in which one element takes the place of another element in a compound – General equation: AX + B → BX + A Ex. 3CuCl 2 + 2Al → 2AlCl 3 + 3Cu 2AgNO 3 (aq) + Zn(s) → 2Ag(s) + Zn(NO 3 ) 2 (aq) Mg(s) + 2HCl(aq) → MgCl 2 (aq) + H 2 (g)

Double-Replacement rxns Double-Replacement rxns - a rxn in which a substance is formed from the exchange of 2 atoms or ions between 2 compounds. – General formula AX + BY → AY + BX Ex. Pb(NO 3 ) 2 + K 2 CrO 4 → PbCrO 4 + 2KNO 3

Combustion Rxn – Combustion Rxns use O 2 as a reactant and always produce CO 2 & H 2 O. In combustion rxns, the products depend on the amount of O 2. – General Combustion rxn formula: C n H 2n+2 + O 2 → CO 2 + H 2 O Ex. 2CH 4 + 4O 2 → 2CO 2 + 4H 2 O

8.3 Activity Series of the Elements Activity series- a list of elements organized according to the ease with which the elements undergo certain chemical reactions.

For metals: greater activity = easy to lose an electron. For non-metals: greater activity = easy to gain an electron.

Predict the products of these Single Replacement rxns. – zinc + lead (II) nitrate – iron + zinc sulphate – lead + copper (II) nitrate – magnesium + zinc chloride – copper + sodium chloride – zinc + iron (II) sulphate – gold + silver nitrate – magnesium + calcium nitrate