Presentation on theme: "Chemical Equations and Reactions"— Presentation transcript:
1Chemical Equations and Reactions CHEMISTRY – Chapter 8Chemical Equations and Reactions
2Chapter 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.
3Chemical ReactionsA process by which one or more substances are changed into one or more different substancesReactants – the original substancesProducts – the resulting substancesMass is always conserved
4Chemical EquationRepresents the identities and relative amounts of reactants and products in a chemical rx
5Chemical Reactions A new substance must be produced The following changes indicate a chemical reaction:Heat and light – release of EProduction of gas – bubblesFormation of a precipitate – a solid produced in a solution that settlesColor change
6Characteristics of Chemical Equations Chemical Equations must do the following:Represent known factsContain the correct formulas for the reactants and productsDiatomic molecules, etc.Law of conservation of mass must be satisfiedAtoms are not created or destroyed, just rearranged
7Word EquationsEquations where products and reactants are represented by wordsQualitativeDoes not give the whole storyNo quantities are givenex. methane + oxygen → carbon dioxide + water
8Formula equationRepresents reactants and products of a chemical rx with symbols or formulasUse coefficients to balanceSmall whole number that appears in front of a formula in an equationex. CH4 + 2 O2 → CO2 + 2 H2O
9Symbols 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) – gasheat→ - reactants are heated0°→ - temperature at which reaction is carried outMnO2→ - catalyst – substance used to alter the rate of rx
10Review and Assignment Assignment: HW 8-1 and HW 8-2 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
11Objectives: 1. Balance a chemical formulas by inspection. Chapter 8 - Section 2Objectives:1. Balance a chemical formulas by inspection.
12Chemical Equations Give us quantitative information Coefficients indicate relative, not absolute amounts of reactants and productsH2 + Cl2 → 2 HCl1 mole of H2 and 1 mole of Cl2Yields 2 moles HClRelative masses of the reactants and products of a chemical rx can be determined from the coefficients1 mole H2 = 2 g H21 mole Cl2 = 71 g Cl2Yields 2 moles HCl = 73 g HClReverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction
13Balancing 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 (H2, N2, O2, F2, Cl2, Br2, I2)3. Balance the formula equation.Balance the different types of atoms one at a time1st balance atoms of elements that are combined and appear only once on each sideBalance polyatomic ions that appear on both sidesBalance H and O atoms4. Count atoms to be sure that the equation is balanced.
16Review and Assignment Assignment: HW 8-3 and HW 8-4 1. Balance a formula equation by inspection.Assignment: HW 8-3 and HW 8-4
17Chapter 8 - Section 2 Objectives: Define and give general equations for synthesis, decomposition, single-replacement, and double-replacement reactions.Classify a reaction as synthesis, decomposition, single-replacement, and double-replacement, or combustion.
18Types of Chemical Reactions 1. Synthesis reactionA + X → AX2. DecompositionAX → A + X3. Single-ReplacementA + BX → AX + BY + BX → BY + X4. Double-ReplacementAX + BY → AY + BX
19Synthesis 2 or more substances combine to produce a new compound Also known as composition reactionForms oxides with oxygen and metals
20DecompositionA single compound undergoes a reaction that produces two or more simpler substancesMost are endothermic when energy is supplied by electricity or heatex. electrolysis – decomposition of a substance by an electric current
21Single-ReplacementOne element replaces a similar element in a compoundAlso called displacementMany are in aqueous solutionsLess E requiredThe more active element replaces the less active oneMost active metals (group 1) react w/water and produce metal hydroxides
22Double-ReplacementIons of two compounds exchange places in an aqueous solution to form two new compoundsOne compound formed is usually a precipitate, an insoluble gas, or a molecular compound (usually water)Other compound remains dissolved
23Combustion ReactionA substance combines with oxygen, releasing a large amount of E in the form of light and heatAlways have oxygen as a reactant
24Review and Assignment1. 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
25Chapter 8 - Section 3 Objectives: Explain the significance of an activity series.Use the activity series to predict whether a given reaction will occur and what the products will be.
26Chemical Activity The ability of an element to react Metals lose e- easilyNon-metals gain e- easily
27Activity SeriesA list of elements organized according to ease with which the elements undergo certain chemical reactionsMetals – greater activity = greater ease to lose e-Non-metals – greater activity = greater ease to gain e-Order is determined by single-replacement reactionsThe metal at the top can replace anything beneath itPredicts if a reaction will actually take placed/o what they are reacting with (water vs. acid)
28Examples 2 Al (s) + 3 ZnCl2(ag) → 3 Zn(s) + 2AlCl3(aq) Al will replace ZnThis reaction will occurCo(s) + 2 NaCl(s) → no reactionCr(s) + H2O(l) → no reaction (b/c water, not steam)
29Examples Zn(s) + H2O(l) 50°C→ Sn(s) + O2(g) → Cd(s) + Pb(NO3)2(aq) → No reaction (b/c water is not steam)Sn(s) + O2(g) →yes, Sn reacts w/oxygenCd(s) + Pb(NO3)2(aq) →yes, Pb is below CdCu(s) + HCl(aq) →no, Cu is below H2
30Review and Assignment Assignment: HW 8-8 Explain the significance of an activity series.Use the activity series to predict whether a given reaction will occur and what the products will be.Assignment: HW 8-8