Presentation on theme: "CHEMISTRY – Chapter 8 Chemical Equations and Reactions."— Presentation transcript:
CHEMISTRY – Chapter 8 Chemical Equations and Reactions
Chapter 8 – Section 1 Objectives: 1. List three observations that suggest that a chemical reaction has taken place. 2. List three requirements for a correctly written chemical equation. 3. Write a word equation and a formula equation for a given chemical reaction.
Chemical Reactions A process by which one or more substances are changed into one or more different substances Reactants – the original substances Products – the resulting substances Mass is always conserved
Chemical Equation Represents the identities and relative amounts of reactants and products in a chemical rx
Chemical Reactions A new substance must be produced The following changes indicate a chemical reaction: Heat and light – release of E Production of gas – bubbles Formation of a precipitate – a solid produced in a solution that settles Color change
Characteristics of Chemical Equations Chemical Equations must do the following: Represent known facts Contain the correct formulas for the reactants and products Diatomic molecules, etc. Law of conservation of mass must be satisfied Atoms are not created or destroyed, just rearranged
Word Equations Equations where products and reactants are represented by words Qualitative Does not give the whole story No quantities are given ex. methane + oxygen → carbon dioxide + water
Formula equation Represents reactants and products of a chemical rx with symbols or formulas Use coefficients to balance Small whole number that appears in front of a formula in an equation ex. CH O 2 → CO H 2 O
Symbols in Chemical Equations → - yields ↔ - reversible reaction – chem rx in which the products reform the originals reactants (s) – solid state ↓ - precipitate (l) – liquid (aq) – aqueous solution (dissolved in water) (g) – gas heat → - reactants are heated 0° → - temperature at which reaction is carried out MnO 2 → - catalyst – substance used to alter the rate of rx
Review and Assignment 1. List three observations that suggest that a chemical reaction has taken place. 2. List three requirements for a correctly written chemical equation. 3. Write a word equation and a formula equation for a given chemical reaction. Assignment: HW 8-1 and HW 8-2
Chapter 8 - Section 2 Objectives: 1. Balance a chemical formulas by inspection.
Chemical Equations Give us quantitative information Coefficients indicate relative, not absolute amounts of reactants and products H 2 + Cl 2 → 2 HCl 1 mole of H 2 and 1 mole of Cl 2 Yields 2 moles HCl Relative masses of the reactants and products of a chemical rx can be determined from the coefficients H 2 + Cl 2 → 2 HCl 1 mole H 2 = 2 g H 2 1 mole Cl 2 = 71 g Cl 2 Yields 2 moles HCl = 73 g HCl Reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction
Balancing Chemical Reactions 1. Identify the names of the reactants and the products, and write a word equation. 2. Write a formula equation by substituting correct formulas for the names of reactants and products. Don’t forget diatomic molecules (H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 ) 3. Balance the formula equation. Balance the different types of atoms one at a time 1 st balance atoms of elements that are combined and appear only once on each side Balance polyatomic ions that appear on both sides Balance H and O atoms 4. Count atoms to be sure that the equation is balanced.
Example 1. zinc + hydrochloric acid → zinc chloride + hydrogen 2. Zn (s) + HCl (aq) → ZnCl 2(aq) + H 2(g) 3. Zn (s) + 2HCl (aq) → ZnCl 2(aq) + H 2(g) 4. 1 Zn + 2H and 2 Cl → 1 Zn and 2 Cl + 2 H
Demo. Zinc + hydrochloric acid → zinc chloride + hydrogen gas Aluminum sulfate + calcium chloride → aluminum chloride + calcium sulfate Balance the equations from the previous demonstrations Zn + HCl → ZnCl 2 + H 2 Zn + 2 HCl → ZnCl 2 + H 2 Al 2 (SO 4 ) 3 + CaCl 2 → AlCl 3 + CaSO 4 Al 2 (SO 4 ) CaCl 2 → 2A lCl CaSO 4
Review and Assignment 1. Balance a formula equation by inspection. Assignment: HW 8-3 and HW 8-4
Chapter 8 - Section 2 Objectives: 1.Define and give general equations for synthesis, decomposition, single- replacement, and double-replacement reactions. 2.Classify a reaction as synthesis, decomposition, single-replacement, and double-replacement, or combustion.
Types of Chemical Reactions 1. Synthesis reaction A + X → AX 2. Decomposition AX → A + X 3. Single-Replacement A + BX → AX + B Y + BX → BY + X 4. Double-Replacement AX + BY → AY + BX
Synthesis 2 or more substances combine to produce a new compound Also known as composition reaction Forms oxides with oxygen and metals
Decomposition A single compound undergoes a reaction that produces two or more simpler substances Most are endothermic when energy is supplied by electricity or heat ex. electrolysis – decomposition of a substance by an electric current
Single-Replacement One element replaces a similar element in a compound Also called displacement Many are in aqueous solutions Less E required The more active element replaces the less active one Most active metals (group 1) react w/water and produce metal hydroxides
Double-Replacement Ions of two compounds exchange places in an aqueous solution to form two new compounds One compound formed is usually a precipitate, an insoluble gas, or a molecular compound (usually water) Other compound remains dissolved
Combustion Reaction A substance combines with oxygen, releasing a large amount of E in the form of light and heat Always have oxygen as a reactant
Review and Assignment 1. Define and give general equations for synthesis, decomposition, single- replacement, and double-replacement reactions. 2. Classify a reaction as synthesis, decomposition, single-replacement, and double-replacement, or combustion. Assignment: WS, HW 8-5, HW 8-7
Chapter 8 - Section 3 Objectives: 1.Explain the significance of an activity series. 2.Use the activity series to predict whether a given reaction will occur and what the products will be.
Chemical Activity The ability of an element to react Metals lose e- easily Non-metals gain e- easily
Activity Series A list of elements organized according to ease with which the elements undergo certain chemical reactions Metals – greater activity = greater ease to lose e- Non-metals – greater activity = greater ease to gain e- Order is determined by single-replacement reactions The metal at the top can replace anything beneath it Predicts if a reaction will actually take place d/o what they are reacting with (water vs. acid)
Examples 2 Al (s) + 3 ZnCl 2(ag) → 3 Zn (s) + 2AlCl 3(aq) Al will replace Zn This reaction will occur Co (s) + 2 NaCl (s) → no reaction Cr (s) + H 2 O (l) → no reaction (b/c water, not steam)
Examples Zn (s) + H 2 O (l) 50°C → No reaction (b/c water is not steam) Sn (s) + O 2(g) → yes, Sn reacts w/oxygen Cd (s) + Pb(NO 3 ) 2(aq) → yes, Pb is below Cd Cu (s) + HCl (aq) → no, Cu is below H 2
Review and Assignment 1.Explain the significance of an activity series. 2.Use the activity series to predict whether a given reaction will occur and what the products will be. Assignment: HW 8-8