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Balancing Equations Section 7.3 in Textbook Chemical Equations The substances involved in a chemical reaction before the change occurs are called the reactants The new substances formed after the change are called the products We say that reactants yield products reactants products yield Using Equations to Represent Reactions Reactants Products C(s) + O2(g) CO2(g) “1 carbon reacts with 1 oxygen molecule yields 1 molecule of carbon dioxide” The letters behind the chemical indicates whether the substance is solid (s) or (cr), liquid (l), aqueous solution (aq), or gas (g). Writing Chemical Equations A chemical equation is a shorthand for the expression of the reaction. For example: Hydrogen gas reacts with Oxygen gas to produce Dihydrogen monoxide. : can be written in shorthand as: H2 + O2 H2O Conservation Obeyed In any chemical reaction, the conservation of mass is observed Principle of the conservation of mass states: matter can not be created or destroyed in a chemical reaction Therefore, the mass of the reactants and the mass products must be the same Coefficients A numbers in front of compounds or elements in a chemical equation represent the number of particles in the reaction The coefficients are used to balance the equation to obey the law of conservation of mass 2 H2 + O2 2 H2O Balancing Equations When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts. Changing the subscripts changes the compound. Steps to Balancing Equations There are four basic steps to balancing a chemical equation. 1.Write the correct formula 2.Find the number of atoms for each element on each side. 3.Determine where to place coefficients. 4.Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced) Some Suggestions to Help You -Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last. -IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) -(Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units Balancing Equations Keep track of the elements in a table, adjusting the amount of atoms as you put in coefficients You must go back and forth putting in coefficients until all of the atoms’ numbers are equal Balancing Equations Practice 2.) Ca(NO3)2 + H2SO4 CaSO4 + HNO3 Balancing Equations Practice 3.) Fe + Cl2 FeCl3 Balancing Equations Practice 4.) Fe + O2 Fe2O3 Balancing Equations Practice 5.) Zn + HCl ZnCl2 + H2 Balancing Equations Practice 6.) Cu + AgC2H3O2 Cu(C2H3O2)2 + Ag Balancing Equations Practice *7.) H2O2 H2O + O2 Balancing Equations Practice *8.) Na + H2O NaOH + H2 Balancing Equations Practice *9.) C2H6 + O2 CO2 + H2O Balancing Equations Practice 10.) Fe + H2O Fe3O4 + H2 Balancing Equations Practice 11.) Al2(SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4