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).

Guidelines for Balancing Chemical Equations 1) polyatomic ions first ? 2) even / odd (make all even) 3) H2O Mg(OH)2 2 H-OH vs. 4) single elements last Example: need 13 oxygen atoms 13 2 “ ” Multiply by O2 = 13 Method for balancing chemical equations 1. Identify the most complex substance. 2. Beginning with that substance, choose an element that appears in only one reactant and one product. Adjust the coefficients to obtain the same number of atoms of this element on both sides. 3. Balance polyatomic ions (if present) as a unit. 4. Balance the remaining atoms, usually ending with the least- complex substance and using fractional coefficients if necessary. If a fractional coefficient is used, multiply both sides of the equation by the denominator to obtain whole numbers for the coefficients. 5. Count the numbers of atoms of each kind on both sides of the equation to be sure that the chemical equation is balanced. 13 2 3X + O2 2Y + Z 3X + O2 2Y + Z 13 2 2 6X + 13 O2 4Y + 2Z

(NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 3 + 6 NH4OH ? 2 (NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 3 + 6 NH4OH ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxide NH41+ OH1- Now you try… 2 AlCl3 + Li2CO3  Al2(CO3)3 + LiCl 3 6

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

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) 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 Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Pb2+ Cl1- K1+ I1- Pb2+ Cl1- K1+ I1- Cl2 Pb I K KCl PbI2 + + 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 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) Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

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

Proportional Relationships Stoichiometry mass relationships between substances in a chemical reaction based on the mole ratio Mole Ratio indicated by coefficients in a balanced equation A balanced chemical equation gives the identity of the reactants and products and the accurate number of molecules or moles of each that are consumed or produced. Stoichiometry is a collective term for the quantitative relationships between the masses, numbers of moles, and numbers of particles (atoms, molecules, and ions) of the reactants and products in a balanced reaction. A stoichiometric quantity is the amount of product or reactant specified by the coefficients in a balanced chemical equation. 2 Mg + O2  2 MgO Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Stoichiometry Steps Core step in all stoichiometry problems!! 1. Write a balanced equation. 2. Identify known & unknown. 3. Line up conversion factors. Mole ratio - moles  moles Molar mass - moles  grams Molarity - moles  liters soln Molar volume - moles  liters gas Mole ratio - moles  moles Core step in all stoichiometry problems!! 4. Check answer. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Stoichiometry Problems How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas? 2KClO3  2KCl + 3O2 ? mol 9 mol 9 mol O2 2 mol KClO3 3 mol O2 = 6 mol KClO3 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

(NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 3 + 6 NH4OH ? 2 (NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 3 + 6 NH4OH ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxide NH41+ OH1- Now you try… 2 AlCl3 + Li2CO3  Al2(CO3)3 + LiCl 3 6

Al2(SO4)3(aq) + 6 NH4OH(aq)  2 Al(OH)3 + 3 (NH4)2SO4 (ppt) (aq) Identify the spectator ions and write a net ionic equation when an aqueous solution of aluminum sulfate is mixed with aqueous ammonium hydroxide. Al3+ SO42- NH41+ OH1- Al3+ OH1- NH41+ SO42- sulfate + hydroxide  aluminum aluminum ammonium ammonium aluminum hydroxide + ammonium sulfate Al2(SO4)3(aq) + 6 NH4OH(aq)  2 Al(OH)3 + 3 (NH4)2SO4 (ppt) (aq) 2 Al3+(aq) + 3 SO42-(aq) + 6 NH41+(aq) + 6 OH1-(aq)  2 Al(OH)3(ppt) + 6 NH41+(aq) + 3 SO42-(aq) “spectator ions” 2 Al3+(aq) + 6 OH1-(aq)  2 Al(OH)3(ppt) Net Ionic Equation

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 117 g

IONIC BONDING: Formation of Magnesium Chloride Cl Cl Mg Mg2+ Cl Cl Loses 2e- Each gains 1e- One magnesium ion Two chloride ions Mg2+ Cl1- [(2+) 2 (1-) = 0] MgCl2 magnesium chloride

IONIC BONDING: Formation of Magnesium Chloride Cl Cl Mg2+ Mg Mg2+ Cl Cl Loses 2e- Each gains 1e- One magnesium ion Two chloride ions Mg2+ Cl1- [(2+) 2 (1-) = 0] MgCl2 magnesium chloride