Chemical Equations & Reactions Chemical Reaction - Study Questions 1. What is a chemical reaction? 2. What is evidence a reaction has occurred? 3. What is a chemical equation? 4. Define reactants. 5. Define products. 6. Define catalyst. 7. What information is found in an equation? 8. What symbols are used to represent the states of matter? 9. What is the meaning of “aq”? 10. How do you indicate a catalyst is being used in a reaction? 11. What is activation energy? 12. What the three things does conservation of matter require of chemical equations? 13. What is the procedure for balancing a chemical equation? 14. Balance the equation for the reaction of magnesium chloride and silver nitrate to form magnesium nitrate and silver chloride. 15. What is a synthesis reaction? 16. How is a combustion reaction related to a synthesis reaction? 17. What type of reaction is an explosion? 18. Compare decomposition and dissociation. 19. What determines whether one metal will replace another in a single displacement reaction? 20. What is the general form of a double displacement reaction? 21. What type of reaction is each of these? 2Na(s) + Cl2(g)  2NaCl(s) PCl5(s)  PCl3(s) + Cl2(g) 2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s) C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O(l) BaCl2(aq) + H2SO4(aq)  2HCl(aq) + BaSO4(s) 22. What is the oxidation number of an element? 23. What is the oxidation number of the fluorine ion? 24. What is the sum of the oxidation numbers in a compound? 31. Can a redox reaction form a molecule? Explain your answer. Chemistry A

Chemical Reactions You should be able to Classify reactions by type. Write a balanced molecular equation, complete ionic equation, and a net ionic equation. Predict products of reactions given the chemical names of the reactants. 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

Organize Your Thoughts Chemical reactions Chemical equations Chemical equations To identify the reactants and products in a chemical equation. To balance a chemical equation with coefficients. To identify synthesis (combination), decomposition, and combustion reactions. To identify single-replacement reactions. To identify double-replacement reactions. To predict the products of a reaction. Synthesis Decomposition Single replacement Double replacement Combustion Balancing equations Predicting products from reactants Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

A Chemical Reaction Reactants Products

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 Objective: To state four observations that are evidence for a chemical reaction. Photo of precipitate: http://www.geocities.com/chem_reactions/Images/Precipitate.jpg

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

Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

Learning Check E3 12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza. How would you write the recipe as an equation?

Solution E3 Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza 12 oz dough + 4 oz mshrm + 12 pep + 8 oz chse 1 pizza + 5 oz tom sauce

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. reactants product 4 Al(s) + 3 O2(g) 2 Al2O3(s) A chemical equation is an expression that gives the identities and quantities of the substances in a chemical reaction Chemical formulas and other symbols are used to indicate the starting material(s) or reactant(s), which are written on the left side of the equation, and the final compound(s) or product(s), which are written on the right side. An arrow, read as yields or reacts to form, points from the reactants to the products. Abbreviations are added in parentheses as subscripts to indicate the physical state of each species:—(s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution. A balanced chemical equation is when both the numbers of each type of atom and the total charge are the same on both sides. A chemical reaction represents a change in the distribution of atoms but not in the number of atoms. http://img.alibaba.com/photo/10784694/Aluminum_Oxide_Abrasive_Fine_Grit_120_220_.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg/600px-Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg http://www.germes-online.com/direct/dbimage/50327532/Aluminum_Alloy_Pipe.jpg 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 Al(s) + 3 O2(g) 2 Al2O3(s) 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 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. The Law of Conservation of Matter Law of Conservation of Matter means that nothing is “lost” or “stolen”. In the real world retail theft costs business lots (much of the theft is actually employee theft)! 20% 100% Chemical Factory 100% 80% 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

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.

Chemical Equations Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. Objectives: To identify seven elements that occur naturally as diatomic molecules, H2, N2, O2, F2, Cl2, Br2, I2. [HOBrFINCL twins or BrINClHOF brothers] To write a chemical equation from the description of a chemical reaction. REACTANTS  PRODUCTS

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? 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 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? 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. http://images.google.com/imgres?imgurl=http://www.uwec.edu/Images/UWECWeb/uwec8.gif&imgrefurl=http://www.uwec.edu/carneymj/Chem103.htm&h=67&w=359&sz=10&hl=en&start=101&tbnid=7T7IE0FudtwTnM:&tbnh=23&tbnw=121&prev=/images%3Fq%3Dgeneral%2Bchemistry%2Bpowerpoint%26start%3D90%26gbv%3D2%26ndsp%3D18%26hl%3Den%26sa%3DN 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).

Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide  bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl2 + NaBr  Br2 + NaCl 3) Determine the coefficients that make the equation balance. Cl2 + 2 NaBr  Br2 + 2 NaCl

Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. ? ? aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al2(SO4)3 + CaCl2  CaSO4 + AlCl3 3) Determine the coefficients that make the equation balance. Al2(SO4)3 + 3 CaCl2  3 CaSO4 + 2 AlCl3

CH4 + 2 O2  CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

Reactants  Products + C(s) + O2(g) CO2(g) + H2(g) + O2(g) H2O (l) 2 2 carbon oxygen carbon dioxide Reactants Product 1 carbon atom 1 carbon atom 2 oxygen atoms 2 oxygen atoms catalyst – speeds up reaction + Pt H2(g) + O2(g) H2O (l) hydrogen oxygen water 2 Pt 2 Reactants Product 4 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Reactants Product 2 hydrogen atoms 2 hydrogen atoms 2 oxygen atoms 1 oxygen atoms Reactants Product 2 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Un balanced

Reactants  Products catalyst – speeds up reaction 2 2 Unbalanced

Showing Phases in Chemical Equations H2O(s) H2O(l) H2O(g) 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)

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 D 2 atm pressure 0 oC MnO2

Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + BC  AC + B element compound compound element BDouble-replacement reaction AB + CD  AD + CB compound compound compound compound Neutralization reaction HX + BOH  BX + HOH Objective: To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization. acid base salt water CH + O2  CO2 + H2O Combustion reaction (of a hydrocarbon) Polymerization Polymer = monomer + monomer + … Ause activity series to predict Bdriving force…water, gas, or precipitate

Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + BC  AC + B BDouble-replacement reaction AB + CD  AD + CB Neutralization reaction HX + BOH  BX + HOH CH + O2  CO2 + H2O Objective: To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization. Combustion reaction (of a hydrocarbon) Polymerization Polymer = monomer + monomer + … Ause activity series to predict Bdriving force…water, gas, or precipitate

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2  2 NaCl Na Na Cl Cl  Cl Cl Na Na General form: A + B  AB element or element or compound compound compound

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2  2 NaCl Na Cl Na+ Cl - Cl Cl - Na+ Na General form: A + B  AB element or element or compound compound compound

Decomposition Reaction 2 H2O + 2 H2 O2 H H O O H + H O O H General form: AB A + B compound two or more elements or compounds

Single and Double Replacement Reactions Single-replacement reaction Mg + CuSO4  MgSO4 + Cu General form: A + BC  AC + B Double-replacement reaction CaCO3 + 2 HCl  CaCl2 + H2CO3 General form: AB + CD  AD + CB

Double Replacement Reaction K2CO3 (aq) Potassium carbonate + BaCl2 (aq) Barium chloride 2 KCl (aq) Potassium chloride + BaCO3 (s) Barium carbonate

Synthesis Reactions Photosynthesis 6 CO2 + H2O C6H12O6 + O2 6 6 Formation of water 2 H2 + O2 H2O 2 Formation of salt http://www.pdphoto.org/jons/pictures2/leaf_1_bg_010503.jpg http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/mass_wasting_erosion/rain_splash_NRCS_p0000003256_small.jpg http://whyfiles.org/111salt/images/salt_magn2.jpg A photomicrograph of common table salt © Carl J. Bowser, Department of Geology and Geophysics, University of Wisconsin, Madison 2 Na + Cl2 NaCl 2 General Form A + B C

Decomposition Reactions Hydrogen Peroxide 2 H2O2 H2O + O2 2 Electrolysis of water H2O H2 + O2 electricity 2 2 Nitrogen triiodide 2 NI3 N2 + I2 3 General Form AB A + B