Balancing Chemical Equations Study Guide

Student Exploration: Balancing Chemical Equations Vocabulary: coefficient, combustion, compound, decomposition, double replacement, element, molecule, product, reactant, single replacement, subscript, synthesis 4 full s'mores cannot be made from 5 cookies and 3 pieces of chocolate. 1. What is wrong with the image below? ___________________________________________ 2. Assuming a s’more requires two graham crackers, one marshmallow, and one piece of 2 chocolate, how many s’mores could you make with the ingredients shown? _____________ Gizmo Warm-up In a chemical reaction, reactants interact to form products. This process is summarized by a chemical equation. In the Balancing Chemical Equations Gizmo, look at the floating molecules below the initial reaction: H2 + O2  H2O. 2 1. How many atoms are in a hydrogen molecule (H2)? ___ 2 2. How many atoms are in an oxygen molecule (O2)? ____ 1 H and 1 O 3. How many hydrogen and oxygen atoms are in a water molecule (H2O)? ________________ 4. In general, what does a subscript (such as the “2” in H2) tell you about the molecule? A subscript tells you how many atoms of that element are present in the molecule. _________________________________________________________________________ 5. A chemical equation is balanced if the number of each type of atom on the left side is equal No to the number of each type on the right side. Is this reaction balanced? ________________ Introduction: The equation H2 + O2  H2O is unbalanced because there are two oxygen atoms on the reactants side of the equation, and only one on the products side of the equation. To balance the equation, you cannot change the structure of any of the molecules, but you can change the number of molecules that are used. Question: How are chemical equations balanced? 1. Balance: Turn on Show histograms. The equation is balanced when there are equal numbers of each type of atom represented on each side of the equation. In the Gizmo, use the up and down arrows to adjust the numbers of hydrogen, oxygen, and water molecules until the equation is balanced. When you are done, turn on Show summary to check your answer. 2 H2 O 1 2 H2 + _____ Write the balanced equation here: _____ O2  _____ 2. Solve: Turn off Show summary. Use the Choose reaction drop down menu to see other equations, and balance them. Check your answers and then write the balanced equations. 6 HCl  _____ 2 3 H2 2 AlCl3 + _____ _____ Al + _____ 2 1 2 _____ NaCl  _____ Na + _____ Cl2 1 Na2S + _____ 1 2 HCl  _____ 2 _____ NaCl + _____ H2S 1 1 CO2 + _____ 2 O2  _____ 2 _____ CH4 + _____ H2O 3. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.) 2 1 2 NaCl A. _____ Na + _____ Cl2  _____ 2 2 2 H2O  _____ 1 H2 B. _____ Na + _____ NaOH + _____ 1 2 2 MgO C. _____ Mg + _____ O2  _____ 2 2 3 O2 D. _____ KClO3  _____ KCl + _____ 2 1 Al2O3 + _____ 3 3 Cu E. _____ Al + _____ CuO  _____ 1 1 2 2 NaI + _____ F. _____ I2 + _____ Na2S2O3  _____ Na2S4O6 6 1 2 G. _____ Mg + _____ P4  _____ Mg3P2 Introduction: Chemical equations show how compounds and elements react with one another. An element is a substance consisting of one kind of atom, such as aluminum (Al) or oxygen gas (O2). A compound is a substance made of more than one kind of atom, such as water (H2O) or table salt (NaCl). Question: How are chemical reactions classified? 1. Match: Most chemical reactions can be classified as one of four types. Using the chemical equations in the Gizmo as a guide, match the following definitions to the type of reaction. B One reactant is broken down into two or ____ more products. A. Synthesis E A fuel is combined with oxygen to ____ produce carbon dioxide and water. B. Decomposition A Two or more reactants combine to form ____ one product. C. Single replacement D Two compounds react to form two ____ different compounds. D. Double replacement C A compound reacts with an element to ____ form a new compound and a different element. E. Combustion 2. Practice: Balance each of the chemical equations below. (Some equations may already be in balance.) In the space to the right, classify the reaction as a synthesis, decomposition, single replacement, or double replacement reaction. 1 AgNO + ___ 1 KNO3 1 KCl  ___ 1 AgCl + ___ A. ___ 3 Double replacement _______________________ 1 H2O + ___ 1 SO3  ___ 1 H2SO4 B. ___ Synthesis _______________________ 1 Cl2  ___ 1 I2 2 KCl + ___ C. ___ 2 KI + ___ Single replacement _______________________ 4 NaHCO  ___ 2 Na CO + ___ 2 H2O + ___ 2 CO2 D. ___ 3 2 3 Decomposition _______________________ 1 H2 1 ZnCl2 + ___ 2 HCl  ___ 1 Zn + ___ E. ___ Single replacement _______________________ 1 BaCl2 + ___ 1 Na2SO4  ___ 1 BaSO4 + ___ 2 NaCl F. ___ Double replacement _______________________ 1 C3H8 + ___ 3 CO2 + ___ 4 H 2O 5 O2  ___ G. ___ Combustion _______________________ 2 3 Cu 3 CuCl2  ___ 2 AlCl3 + ___ H. ___ Al + ___ Single replacement _______________________