VIEWS: 49 PAGES: 40 POSTED ON: 8/15/2010
Balancing Equations Balancing, Writing, and Naming Equations What is balanced in a chemical equation? Three things are balanced in a chemical equation: 1. Atoms 2. Mass 3. Charge Balancing Equations Balancing Equations Law of Conservation of Matter: In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, the amount of reactants equal the amount of products. Balancing Equations Paraphrase: Law of Conservation of Atoms: The number of atoms of each type of element must be the same on each side of the equation. Counting Atoms How many atoms of each element are in the following molecules? 1. H2SO4 2. Ca(OH)2 3. NaCl 4. (NH3)3P04 5. 3H2O 6. 4Al2(CO3)3 Answers 1. 2 hydrogen, 1 sulfur, 4 oxygen 2. 1 calcium, 2 oxygen, 2 hydrogen 3. 1 sodium, 1 chlorine 4. 3 nitrogen, 9 hydrogen, 1 phosphorus, 4 oxygen 5. 6 hydrogen, 3 oxygen 6. 8 aluminum, 12 carbon, 36 Balancing Equations Hydrogen + oxygen water H2 + O2 H2O Hydrogen and oxygen are diatomic elements. Their subscripts cannot be changed. The subscripts on water cannot be changed. Balancing Equation H2 + O2 H2O Count the atoms on each side. Reactant side: 2 atoms H and 2 atoms O Product side: 2 atoms H and 1 atom O Balancing Equations H2 + O2 H2O If the subscripts cannot be altered, how can the atoms be made equal? Adjust the number of molecules by changing the coefficients. Balancing Equations Balancing hints: Balance the metals first. Balance the ion groups next. Balance the other atoms. Save the non ion group oxygen and hydrogen until the end. Is this equation balanced? NaCl + H2O NaOH + Cl2 left side has 1Na, 1Cl, 2H, and 1O right side has 1Na, 1O, 1H, and 2Cl NO!!!!!! It is not balanced!! Is this equation balanced? HCl + NaOH NaCl+ H2O left side has 2H, 1Cl, 1Na, and 1O right side has 1Na, 1Cl, 2H, and 1O Yes!!!!!! It is balanced!! Is this equation balanced? Ca + H2O Ca(OH)2 + H2 left side has 1Ca, 2H, 1O right side has 1Ca, 2O, 4H No!!!!!! It is not balanced!! How can we make it balance???? Balancing Equations H2 + O2 2H2O Reactants: 2 atoms of H and 2 atoms of O Products: 4 atoms of H and 2 atoms of O H is no longer balanced! Balancing Equations 2H2 + O2 2H2O Reactant side: 4 atoms of H and 2 atoms of O Product side: 4 atoms of H and 2 atoms of O It’s Balanced! Balancing Equations N2 + H2 NH3 Nitrogen + hydrogen ammonia Count atoms. Reactants: 2 atoms N and 2 atoms H Products: 1 atom N and 3 atoms of NH3 Balancing Equations Nothing is balanced. Balance the nitrogen first by placing a coefficient of 2 in front of the NH3. N2 + H2 2NH3 Balancing Equations Hydrogen is not balanced. Place a 3 in front of H2. Reactant side: 2 atoms N, 6 atoms H Product side: 2 atoms N, 6 atoms H N2 + 3H2 2NH3 Balancing Equations Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 Count atoms. Reactants: Ca – 3 atoms, P – 2 atoms, O – 8 atoms; H – atoms, S – 1 atom, O – 4 atoms Balancing Equations Side note on Ca3(PO4)2 The subscript after the phosphate indicates two phosphate groups. This means two PO43- groups with two P and eight O atoms. Balancing Equations Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 Count atoms in the product. Ca atoms – 1, S atom – 1, O atoms – 4; H atoms – 3, P atom – 1, O atoms - 4 Balancing Equations In this equation, the ion groups do not break up. Instead of counting individual atoms, ion groups may be counted. Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 Balancing Equations Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 Reactants: Ca2+ – 3, PO43- - 2, H+ – 2, SO42+ - 1 Products: Ca2+ - 1, SO42- - 1, H+ - 3, PO43- -1 Balancing Equations Balance the metal first by placing a coefficient of 3 in front of CaSO4. Products: Ca – 3 atoms, SO42- - 3 groups Ca3(PO4)2+ H2SO4 3CaSO4 + H3PO4 Balancing Equations Three sulfate groups are needed on the reactant side so place a coefficient of 3 in front of H2SO4. 3H2SO4 gives 6 H+ and 3 SO42-. Neither phosphate nor calcium is balanced. Ca3(PO4)2 + 3H2SO4 3CaSO4 + H3PO4 Balancing Equations A coefficient of 2 placed in front of H3PO4 which balances both hydrogen and phosphate. Ca3(PO4)2+ 3H2SO4 3CaSO4 + 2H3PO4 Balancing Equations Cu + H2SO4 CuSO4 + H2O + SO2 The sulfate group breaks up. Each atom must be counted individually. Ugh! Reactants: Cu – 1, H – 2, S – 1, O – 4 Products: Cu – 1, S – 1, O - 4, H – 2, O – 1, S – 1, O - 2 Balancing Equations Sulfur is not balanced. Place a two in front of sulfuric acid. Count atoms: 2 H2SO4 H – 4, S – 2, O-8 Cu + 2H2SO4 CuSO4 + H2O + SO2 Balancing Equations Hydrogen needs to be balanced so place a 2 in front of the H2O. Count the number of atoms. Cu + 2H2SO4 CuSO4 + 2H2O + SO2 Balancing Equations Reactants: Cu – 1, H – 4, S – 2, O – 8 Products: Cu – 1, S – 1, O – 4, H – 4, O – 2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O –8 It’s balanced! Cu + 2H2SO4 CuSO4 + 2H2O + SO2 Balancing Equations This method of balancing equations is the inspection method. The method is trial and error. Practice. Writing and Naming Nickel + hydrochloric acid Nickel(II) chloride + hydrogen Write the corresponding formula equation and then balance the equation. Writing and Naming Write each formula independently. Ignore the rest of the equation. Balance the equation after writing the formulas. Ni + HCl NiCl2 + H2 Ni + 2HCl NiCl2 + H2 Writing and Naming Remember the diatomic elements: H2, N2, O2, F2, Cl2, Br2, and I2. Writing and Naming Cu + H2SO4 CuSO4 + H2O + SO2 Balance the formula equation. Write the word equation. Writing and Naming Cu + 2H2SO4 CuSO4 + 2H2O + SO2 Write the names: Cu by itself is just copper. Copper(I) or copper(II) would be incorrect. H2SO4 should be named as an acid. Sulfuric acid Writing and Naming CuSO4 has a SO42- group so Cu must be 2+. Some metals must have Roman Numerals. Copper(II) sulfate H2O is known as water. SO2 is a nonmetal compound. Its name is either sulfur dioxide or sulfur(IV) oxide. Writing and Naming Cu + 2H2SO4 CuSO4 + 2H2O + SO2 Copper + sulfuric acid Copper(II) sulfate + water + sulfur dioxide Balancing Equations Chapter 8 Practice! Practice! Practice!
"Balancing Equations - PowerPoint"