Warm Up 01/19/2017 In your journal, write about the importance of nomenclature. You have about 5 minutes to complete this and I will come around to check it.

Unit 5 - Introduction to Chemical Reactions Module 2: Conservation of Mass in Chemical Reactions and Balancing Chemical Equations

Law of the Conservation of Mass Mass cannot be created or destroyed in chemical reactions Matter can be and is changed by the rearrangement of atoms, but the mass cannot change Therefore, the same atoms of matter still exist after a chemical reaction as were present before the reaction

Balancing a Chemical Reaction Equations describe chemical reactions showing the reactants and products Since mass must be conserved, the same number of atoms of each element must be present in the products as were in the reactants Individual atoms do not react alone – many atoms react at the same time Atoms are counted using moles The number of moles of each reactant and product must be adjusted to have the same number of atoms on both sides of the reaction That process is known as balancing the reaction

How Are Reactions Balanced? It is a process of counting atoms The chemical formula of the compounds or elements cannot be changed – you may not change anything about the reactants or the products themselves Only the coefficients (the number of moles) can be changed Changing the number of moles (coefficients), changes the number of atoms of every element in the compound Coefficients (moles) are changed until the same number of each atom are on both sides of the reaction

Balancing Process List the elements involved in the reaction Count the number of moles of each element on both sides of the reaction Adjust the number of moles using coefficients so that the first element is balanced Recount the number of moles of each element Repeat the process until the same number of moles is present for every element in the reaction Check the result to make sure that the balanced reaction is the lowest whole number ratio of the reactants and products

Steps to Balancing a Chemical Equation Step 1: Write a chemical formula for the reactions using formulas and symbols Hydrogen and Oxygen combine to make water H2 (g) + O2 (g) H2O (l) Step 2: Count the atoms in reactants and products Numbers and Kinds of Atoms H2 (g) + O2 (g) H2O (l) H 2 O 1

Steps to Balancing a Chemical Equation Step 3: Choose coefficients that balance the equation Remember, never change subscripts of a correct formula to balance an equation H2 (g) + O2 (g) H2O (l) 2H2 (g) + O2 (g) 2H2O (l) Step 4: Check the result to make sure that the balanced reaction is the lowest whole number ratio of the reactants and products

Steps to Writing and Balancing a Chemical Equation Step 1: Identify the type of reaction Reaction: magnesium bromide and sodium fluoride produce magnesium fluoride and sodium bromide This is a double replacement reaction Step 2: Identify whether reactants and products are ionic or covalent compounds All are ionic compounds Step 3: Write elements with oxidation numbers Magnesium bromide: Mg+2 and Br‐1 Sodium fluoride: Na+1 and F‐1 Magnesium fluoride: Mg+2 and F‐1 Sodium bromide: Na+1 and Br‐1

Steps to Writing and Balancing a Chemical Equation Step 4: Write compounds. Be sure charges balance out to zero! Because Mg+2 has an overall positive charge of +2, you must have a negative charge of ‐2 to balance out to zero. You need 2 atoms of Br‐1 This compound becomes MgBr2 Na+1 and F‐1 becomes NaF Mg+2 and F‐1 becomes MgF2 Na+1 and Br‐1 becomes NaBr Step 5: Write out the equation MgBr2 + NaF è MgF2 + NaBr Step 6: Balance the equation MgBr2 + 2NaF è MgF2 + 2NaBr