2What is a reaction?A chemical reaction occurs when the bonds between the outermost parts of atoms are formed or brokenChemical reactions involve changes in matter, the making of new materials with new properties, and energy changesThe equation for a reaction shows the reactants and products as well as their relative amounts within the reaction
3ReactantsThe reactants in a chemical equation are the atoms that react to form a different substanceThey will typically be on the left hand side of the equationIn word equations the reactants will also typically be mentioned first
4ExampleIodine crystals react with chlorine gas to produce iodine trichloride.The reactants are iodine crystals and chlorine gasI2 and Cl2
5ProductsThe products in a chemical reaction are what is formed from the reactionIn a chemical equation they will typically be on the rightIn word equations they are usually listed after the reactants to show what the reactants “created” (created is in quotes for a reason)
6Example We will use the same previous example: Iodine crystals react with chlorine gas to produce iodine trichloride.The product in this reaction would be iodine trichlorideICl3
7Iodine + Chlorine Iodine trichloride Word EquationsWhen writing a word equation, and eventually a chemical equation, you will place reactants on one side and products on the otherIodine crystals react with chlorine gas to produce iodine trichloride.In our example we would have end up having:Iodine + Chlorine Iodine trichloride
8The plus sign indicates that two items on that particular side of the equation are separate but within the same reactionThe arrow indicates the direction of the reactionThere are also situations where there are two arrows pointing in the opposite directions, but we are not going into those yet
9Practice Sodium metal and chlorine gas react to form sodium chloride Iron metal and chlorine gas yield iron III chlorideWater is formed when hydrogen and oxygen gases reactSodium chloride and lead II nitrate react to produce lead II chloride and sodium nitrate
10Answers Sodium + Chlorine Sodium Chloride Iron + Chlorine Iron III ChlorideHydrogen + Oxygen Water (dihydrogen monoxide)Sodium Chloride + Lead II Nitrate Lead II Chloride + Sodium Nitrate
11Real chemical equations Chemists do not write out the words each time for two reasons:First, its time consuming. Using shorthand symbols like the chemical symbols we have been using for the last few months is quickerSecond, the chemical symbols tell us more about the molecule and make spotting reaction types often easier than when using words
12So in order to write a word equation as a chemical equation, all you simply have to do is replace the words with their respective chemical symbolsRemember that there will be ionic compounds, covalent compounds, and there will be polyatomic ions present in many equations as well. Do not forget how to identify them and when to use parenthesis!
13Iodine + Chlorine Iodine trichloride ExampleIodine crystals react with chlorine gas to produce iodine trichloride.The word equation was:Iodine + Chlorine Iodine trichlorideThis means our chemical equation will be:I2 + Cl2 ICl3
14Our practice examples Sodium + Chlorine Sodium Chloride Iron + Chlorine Iron III ChlorideHydrogen + Oxygen Water (dihydrogen monoxide)Sodium Chloride + Lead II Nitrate Lead II Chloride + Sodium Nitrate
19Balancing an equationThe law of conservation of matter states that matter can neither be created nor destroyedThis means that the previous chemical equations were not correct due to their lack conservationSome of them had one or two different amounts of the same elements on the opposite sides of the SAME EQUATION!This cannot happen
20When balancing an equation you can only manipulate the coefficients Fe2O CO 3 CO FeThe underlined numbers are the coefficientsYou CANNOT CHANGE THE SUBSCRIPTS!
21What is on one side must be on the other This means you cannot have sodium on one side and not on the otherBack to our group example:Iodine + Chlorine Iodine trichlorideWhich became:I2 + Cl2 ICl3
22Steps to Balancing Equations Assemble the correct formulas for all the reactants and products, using “+” and “→”Count the number of atoms of each type appearing on both sidesBalance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!(hint: Some prefer to save O until the very last)Double-Check to make sure it is balanced.
23Balance itI2 + Cl2 ICl3First, we’ll balance out the chlorines by adding a coefficientI Cl2 ICl3Still not balanced yet. We have six chlorines in the reactant, but only 3 in the products. Add another coefficientI Cl2 2 ICl Now count the atomsReactants: 2 I and 6 ClProducts: 2 I and 6 Cl Balanced!