Lesson Tasks Complete the Chemical Equations worksheet using the information in this PPT. Take 1 page of notes, highlighting key point Answer review questions on slide: Chemical Reactions Video with Transcript Annotation Files are on the Class Website

Chemical Equations & Reactions Objective: To write balanced chemical equations by inspection. Balanced chemical equation: – Provides qualitative information about the identities and physical states of the reactants and products – Provides quantitative information because it tells the relative amounts of reactants and products consumed or produced in the reaction – The number of atoms, molecules, or formula units of a reactant or product in a balanced chemical equation is the coefficient of that species – Mole ratio of two substances in a chemical reaction is the ratio of their coefficients in the balanced chemical equation Chemical Equations & Reactions

Chemical Reactions You should be able to Classify reactions by type. Write a balanced molecular equation, complete ionic equation, and a net ionic equation. Balance oxidation-reduction reactions. Predict if a precipitate will form using the solubility rules. Predict products of reactions given the chemical names of the reactants.

Organize Your Thoughts Chemical reactions Chemical equations Chemical equations Synthesis Decomposition Single replacement Double replacement Combustion Balancing equations Predicting products from reactants

Describing a Chemical Reaction Indications of a Chemical Reaction Evolution of heat, light, and/or sound Production of a gas Formation of a precipitate Color change

Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse

Chemical Equations Depict the kind of reactants and products aluminum oxide Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Objectives: To explain the concept of an activity series for metals. To predict whether a single-replacement reaction occurs by referring to the activity series. The Activity Series – Predicts the outcome of the single-displacement reactions – Arranges metal and hydrogen in decreasing order of their tendency to be oxidized – Active metals at the top of the series have the greatest tendency to lose electrons; these including alkali metals (Group 1), alkaline earths (Group 2), and Al (Group 13). – Inert metals at the bottom of the series have the lowest tendency to be oxidized; these include precious metals or coinage metals located in the lower-right portion of the metals in the periodic table. – Any element will reduce compounds of the elements below it in the series. – Only those metals that lie above hydrogen in the activity series dissolve in acids to produce H2. The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.

Chemical Equations 4 Al(s) + 3 O2(g) 2 Al2O3(s) aluminum oxide sandpaper 4 g Al + 3 g O2 yield 2 g Al2O3 This equation means: 4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 or 4 Al moles + 3 O2 moles yield 2 moles of Al2O3 4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol 108 g + 96 g = 204 g

Chemical Equations The Law of Conservation of Matter Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. CHEMICAL EQUATION indicates the reactants and products of a reaction. The Law of Conservation of Matter 20% 100% Chemical Factory 100% 80% REACTANTS → PRODUCTS Kotz web

Chemical Equations Because of the principle of the conservation of matter,An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 “Father of Modern Chemistry”

Characteristics of Chemical Equations The equation must represent known facts. The equation must contain the correct formulas for the reactants and products. The law of conservation of mass must be satisfied.

Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactant Product CH4 + 2 O2 CO2 + 2 H2O

Unbalanced and Balanced Equations H Cl Cl H Cl Cl H H H2 + Cl2 → HCl (unbalanced) H2 + Cl2 → 2 HCl (balanced) reactants products H Cl reactants products H Cl 2 1 2 2 2 1 2 2

Visualizing a Chemical Reaction 2 Na + Cl2 NaCl 2 ___ mole Na 10 10 ___ mole Cl2 5 5 ___ mole NaCl 10 10 ?

Visualizing a Chemical Reaction 2 Na + Cl2 NaCl 2

Meaning of Chemical Formula Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O → 2 NaOH + H2 2 Na + 2 H2O → 2 NaOH + H2

Balancing Chemical Equations Write a word equation for the reaction. Write the correct formulas for all reactants and products. Determine the coefficients that make the equation balance.

Balancing Chemical Equations Other examples NO(g) + O2(g) → NO2(g) is it balanced? Is this balanced? NO(g) + O(g) → NO2(g) Is this OK? A reaction that yields an insoluble product, a precipitate, when two solutions are mixed Are a subclass of exchange reactions that occur between ionic compounds when one of the products is insoluble Used to isolate metals that have been extracted from their ores and to recover precious metals for recycling Is this balanced? NO(g) + ½ O2(g) → NO2(g) Is this OK?

Balancing Chemical Equations An important point to remember 2 NO(g) + O2(g) → 2NO2(g) The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation. It is a “multiplier” for every atom in the molecule. A reaction that yields an insoluble product, a precipitate, when two solutions are mixed Are a subclass of exchange reactions that occur between ionic compounds when one of the products is insoluble Used to isolate metals that have been extracted from their ores and to recover precious metals for recycling The subscript 2 in O2 (g) and NO2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).

Showing Phases in Chemical Equations Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g) H2O(s) H2O(l) H2O(g)

Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction Δ 2 atm pressure 0 oC MnO2

Formation of a solid: AgCl AgNO3(aq) + KCl(aq) → KNO3 (aq) + AgCl(s)

Pb2+ Cl1- K1+ I1- Pb2+ Cl1- K1+ I1- Cl2 Pb I K KCl PbI2 + + lead (II) chloride + potassium iodide potassium chloride + lead (II) iodide Pb2+ Cl1- K1+ I1- Pb2+ Cl1- K1+ I1- Cl2 Pb + I K KCl + PbI2 (aq) (ppt)

Potassium reacts with Water P O W !

Meaning of Coefficients 2 atoms Na 1 molecule Cl2 2 molecules NaCl 2 Na + Cl2 2 NaCl 2 g sodium + 1 g chlorine = 2 g sodium chloride 2 mol sodium 1 mol chlorine 2 mol sodium chloride (2 mol Na) x (23 g/mol) (1 mol Cl2) x (71 g/mol) (2 mol NaCl) x (58.5 g/mol) 46 g 71 g 117 g What you should learn: In chemical change atoms are rearranged but no atoms are created and none are destroyed Chemical equations are symbolic representations of what is happening at the molecular level and are used to communicate the conditions under which a reaction proceeds, the products and amount of energy that results, and allow for predictions to be made. More Specifically...: Classify those equations that come under the heading of synthesis, decomposition, single replacement, double replacement, neutralization, oxidation/ reduction and combustion Identify and name acids and bases Use principle of conservation of mass to balance a reaction From a written description of a reaction write a balanced reaction using correct state symbols Show that the conservation of mass is true for a balanced reaction Predict the products of chemical reactions (including state symbols) when given the reactants. Use an activity series to predict the spontaneity of reactions. Use solubility rules to predict the formation of a precipitate Define oxidation and reduction, and identify any species undergoing oxidation or reduction, and identify the oxidizing and reducing agents Write half reactions for single replacement reactions (monoatomic ions only) Fast Track to a 5 (page 61) To know how to calculate the molecular mass of a covalent compound and the formula mass of an ionic compound To be able to use the concepts of the mole and molar mass to calculate the number of atoms, molecules, or formula units in a sample of a substance To be able to determine the empirical formula of a compound from its composition by mass To know how to derive the molecular formula of a compound from its empirical formula To be able to describe a chemical reaction To know how to calculate the quantities of compounds produced or consumed in a chemical reaction To identify fundamental types of chemical reactions To begin to predict the types of chemical reactions that substances undergo 117 g

Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustion Reactions

Summary of Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Acid-Base Reactions Combustion Reactions Synthesis reactions (Reactants are elements.) Decomposition reactions (Products are elements.)

A Mixture of Molecules

Review Questions Define catalyst. What information is found in an equation? What symbols are used to represent the states of matter? What is the meaning of “aq”? How do you indicate a catalyst is being used in a reaction? What is activation energy? What the three things does conservation of matter require of chemical equations? What is the procedure for balancing a chemical equation? What is a synthesis reaction? How is a combustion reaction related to a synthesis reaction? What type of reaction is an explosion? Compare decomposition and dissociation. What determines whether one metal will replace another in a single displacement reaction? What is the general form of a double displacement reaction?