Technical Science Introduction to Chemistry Chemical Equations slides 1-18 By John W. Pluemer

Chemical Equations In this tutorial you will… Analyze a Chemical Equation Prove a Chemical Equation is Balanced Explain Reasons for Balancing Equations Explore Common Chemical Reactions

Analyze a Chemical Equation 1 of 5 Analyze a Chemical Equation Home One of the main functions of chemistry is to determine what will happen when substances react. A chemical equation is the method used to express what happens during a chemical reaction. The chemical equation below outlines a familiar chemical reaction. What is this telling you? 2Na + Cl2  2NaCl A chemical equation is really just a recipe. It tells you the amounts of specific ingredients that are required to make a certain amount of a product.

Analyze a Chemical Equation 2 of 5 Analyze a Chemical Equation Let’s take a closer look at that chemical equation. 2Na + Cl2  2NaCl Reactants Products The “results” on the right side of the equation are called the Products First, you should notice that the equation is broken into two parts with an arrow. The arrow represents the chemical reaction. The “ingredients” on the left side of the equation are called the Reactants

Analyze a Chemical Equation 3 of 5 Analyze a Chemical Equation Identify the reactants and the products in the following reactions. N2 + 3H2  2NH3 BaCO3  BaO + CO2 MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O Reactants Products

Analyze a Chemical Equation 4 of 5 Analyze a Chemical Equation Let’s take another look at that chemical equation. 2Na + Cl2  2NaCl Coefficients Subscripts The subscripts in this equation tell us… Na is in elemental form. 2 Cl atoms are bonded to form a molecule of chlorine gas. 1 Na is bonded to 1 Cl to make a molecule of sodium chloride. The small numbers following the chemical symbols are called Subscripts. (Subscripts of one are not written out.) Subscripts tell the number of atoms that are bonded together to make a single molecule of a substance. They determine the substance itself. The coefficients in this equation tell us… Two sodium atoms will react with One chlorine molecule to produce Two molecules of sodium chloride. You probably noticed the numbers associated with chemical formulas for the reactants and the products. Coefficients tell the number of atoms or molecules that are required for the reaction. Coefficients are the amounts of the reactants and products. The large numbers in front of the formulas are called Coefficients. (Coefficients of one are not written out.)

Analyze a Chemical Equation 5 of 5 Analyze a Chemical Equation Home What do the chemical equations below tell you? N2 + 3H2  2NH3 (NH3 is Ammonia) 2MgO + 4Si  2Mg + SiO2 1 molecule of nitrogen gas reacts with 3 molecules of hydrogen gas to form 2 molecules of ammonia. Nitrogen and hydrogen molecules are each formed from 2 atoms bonded together. Ammonia is formed from 1 N atom bonded to 3 H atoms. 2 molecules of Magnesium Oxide (each with 1Mg bonded to 1 O) react with 4 atoms of silicon to form 2 atoms of magnesium and 1 molecule of silicon dioxide (having 1 Si bonded to 2 O)

Remember: coefficients of 1 are not written out. Prove a Chemical Equation is Balanced Home An equation must be balanced to be useful. Remember: coefficients of 1 are not written out. The equation below is not balanced. Can you see what is missing? Na + Cl2  NaCl 2 1 2 There are no coefficients in the equation above. Coefficients determine the amounts of reactant and product. The amounts of reactant and product are correct when the coefficients make the equation balance.

Prove a Chemical Equation is Balanced 2 of 6 Prove a Chemical Equation is Balanced Prove the equation is balanced. 2Na + Cl2  2NaCl Atom Reactant Product Na 2 2 Cl 2 2 The Coefficient of 2 and the lack of subscripts, tells us there are 2 molecules of sodium chloride. Each molecule has 1 Na and 1 Cl. This gives a total of two sodium atoms and two chlorine atoms on the product side. Third: Count the number of atoms of each type on the product side. You will consider both coefficients & subscripts This reaction is balanced because there are same number and types of atoms on each side. Second: Count the number of atoms of each type on the reactant side. You will consider both coefficients & subscripts Remember, a balanced chemical equation has the same type and number of atoms on both the reactant and product sides. We need to keep track of types and numbers of atoms on each side of the equation. So… Let’s get organized by creating a table First: Identify the all of the different elements that are involved in this reaction. There are 2 types of atoms: Sodium & Chlorine The lack of a subscript and the coefficient of 2 on sodium, tells us that there are 2 Na atoms on the reactant side. The subscript of 2 and the lack of a coefficient on chlorine, tells us that there is one molecule of chlorine that contains 2 Cl atoms.

Prove a Chemical Equation is Balanced 3 of 6 Prove a Chemical Equation is Balanced Prove the equation is balanced. MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O Atom Reactant Product Mn 1 1 O 2 2 H 4 4 Cl 4 2 4 Remember, a balanced chemical equation has the same type and number of atoms on both the reactant and product sides. There are a total of 4 chlorine atoms on the product side of the equation; 2 from the MnCl2 and 2 from the Cl2. This reaction is balanced because there are same number and types of atoms on each side. Chlorine shows up in two products MnCl2 & Cl2. Cl2 tells us there is 1 molecule of chlorine gas with 2 Cl atoms bonded together. MnO2 tells us that there is one molecule of this compound and it has one manganese bonded to two oxygens. MnCl2 tells us there is one molecule that has 1 manganese bonded to 2 chlorines. So, there is 1Mn atom and 2 Cl atoms. 2H2O tells us that there are two molecules each having one oxygen bonded to two hydrogens. So there are four hydrogen and two Oxygen 4HCl tells us that there are four molecules each having one hydrogen bonded to one chlorine. So there are four hydrogen and four chlorine. Second: Count the number of atoms of each type on the reactant side. You will consider both coefficients & subscripts We need to keep track of types and numbers of atoms on each side of the equation. So… Let’s get organized by creating a table First: Identify the all of the different elements that are involved in this reaction. There are 4 types of atoms: Mn, O, H, & Cl Third: Count the number of atoms of each type on the product side. You will consider both coefficients & subscripts

Prove a Chemical Equation is Balanced 4 of 6 Prove a Chemical Equation is Balanced Prove the following reaction is balanced. 2NO + 2CO  N2 + 2CO2 Atom Reactant Product N 2 2 O 4 4 C 2 2

Prove a Chemical Equation is Balanced 5 of 6 Prove a Chemical Equation is Balanced Prove the following reaction is balanced. P4O10 + 4HNO3  4HPO3 + 2N2O5 Atom Reactant Product P 4 4 O 22 22 H 4 4 N 4 4

Prove a Chemical Equation is Balanced 6 of 6 Prove a Chemical Equation is Balanced Home Prove the following reaction is balanced. C6H12O6 + 6O2  6CO2 + 6H2O Atom Reactant Product C 6 6 H 12 12 O 18 18

Explain Reasons for Balancing Equations 1 of 5 Explain Reasons for Balancing Equations Home You know that a reaction is balanced when the coefficients make the number and type of atoms on each side of the equation equal. 2Na + Cl2  2NaCl You can also prove whether a reaction is balanced. But why is it so important to balance an equation? Why wouldn’t you want to write the equation like this… Na + Cl2  NaCl There are at least three reasons why it is important to balance a chemical reaction.

Now we are following The Law of Conservation of Matter. Explain Reasons for Balancing Equations Look at the unbalanced equation below. Na + Cl2  NaCl 2 2 Na Na Cl Na Cl Na Cl Now we are following The Law of Conservation of Matter. The Law of Conservation of Matter. This law states that matter can not be created or destroyed only changed in form. Where did that other chlorine go? It has to go somewhere. It can’t just disappear. This leads us to a very important law in chemistry. When the proper coefficients are in place and the equation is balanced, all the atoms can be accounted for. This means if we start with two atoms of chlorine we must end with two atoms of chlorine. The unbalanced equation above suggests that an atom of chlorine just disappeared. This is against the law. Notice there are two chlorine atoms on the reactant side but only 1 chlorine on the product side.

What coefficient in front of the H2 would make this equation balance? Explain Reasons for Balancing Equations Look at the partially balanced equation below. 2Fe + 3H2O  Fe2O3 + H2 3 Fe Fe O H O-Fe-O-Fe-O H-H H-H O H O H H-H Notice in this partially balanced equation that the iron and the oxygen are balanced. However, the hydrogens from water on the reactant side are not accounted for on the product side. Where did those hydrogen atoms go? As it turns out, the hydrogen atoms bonded together to form another product: Hydrogen Gas (H2) Hydrogen gas is odorless and colorless but explosive. That’s not a product you would want to overlook. What coefficient in front of the H2 would make this equation balance? If a chemical equation is not properly balanced, you may miss a potential product.

Explain Reasons for Balancing Equations 4 of 5 Explain Reasons for Balancing Equations What does the unbalanced reaction below tell you? Na + Cl2  NaCl 2 2 Na Na Cl-Cl Na-Cl Na-Cl An unbalanced equation is like a recipe that tells you all the ingredients but doesn’t tell you how much of each one to use Balancing the equation tell us how much of each reactant is required and how much of each product will be produced. Remember, chemical equations are recipes. They tell the amounts of the ingredients required and the amounts of product you can expect. This reaction, as written, tells you that sodium atoms (Na) react with chlorine gas molecules (Cl2) to form molecules of sodium chloride (NaCl) The amounts of each substance are determined by the coefficients that are assigned when the equation is balanced. We know the ingredients and products but we don’t know how much of each is needed.

Explain Reasons for Balancing Equations 5 of 5 Explain Reasons for Balancing Equations Home Why is it important to work with a balanced chemical equation? If an equation isn’t balanced, it implies that atoms suddenly appear or disappear. This goes against the Law of Conservation of Matter If an equation isn’t balanced, you may miss a product that is not easily observed. An equation is a chemical recipe. If it isn’t balanced, it is like a recipe that doesn’t include any amounts. It would be useless to try to make something from such a recipe.

Technical Science Introduction to Chemistry You have Completed Chemical Equations Created by John W. Pluemer