Presentation on theme: "What is a Chemical Reaction?"— Presentation transcript:
1 What is a Chemical Reaction? Two atoms can be mixed together to create a new compound (sodium & chlorine)Can also mix two compounds to create new compounds (baking soda & vinegar)New substances are produced in each case with properties different from the original substances.
2 Dalton’s Atomic Theory All matter is made up of small particles called atomsAtoms cannot be created, destroyed, or divided into smaller particlesAll atoms of the same element are identical in mass and size, but different in mass and size from atoms of other elementsJohn Dalton
3 Conservation of Mass Law of conservation of mass states: The total mass of the reacting substances (the reactants) is always equal to the total mass of the resulting substances (the products).Matter is neither created or destroyed in a chemical reaction.Atoms in the reactants are present in the products.
4 Writing Chemical Equations Lets look at how water is formed.First we can look at the word equation.Hydrogen + Oxygen WaterReactants on the left side of the arrowProducts on the right side of the arrowPlus sign means “reacts with”Arrow means “produce”
5 The Hindenburg Zeppelin Hydrogen + Oxygen WaterVideo on File
6 Diatomic Molecules Hydrogen - H2 Chlorine - Cl2 Oxygen - O2 Atoms can share electrons with the same atom.These molecules have two of the same atoms joined by a covalent bond.Since there are two of the same atoms the word diatomic is used. (“di” meaning two)Seven elements are diatomic:Hydrogen - H2Chlorine - Cl2Oxygen - O2Bromine - Br2Nitrogen - N2Iodine - I2Fluorine - F2
7 Skeleton Equations For water the skeleton equation is: H2 + O2 H2O According to Conservation of Mass the reactants and products must have the same number of atoms.We must balance the chemical equation.This is done by adding coefficients in front of the compounds.
8 Balancing the Reaction Important: Subscripts CANNOT be changed!!!!!!Hydrogen is balanced so you must balance the oxygen by adding another water moleculeH2 + O2 2H2ONow hydrogen is not balanced so we must add another hydrogen molecule2H2 + O2 2H2O
9 Check The AtomsAdd up all the atoms of both reactants and products to make sure the amounts are the same.2H2 + O2 2H2OReactants2 H2 Molecules4 H atoms1 O2 Molecule2 O atomsProducts2 H2O molecules4 H atoms2 O atoms
10 Tips for BalancingAdjust co-efficients, not chemical formulas (subscripts).Balance metals firstAdd co-efficients to individual elements lastIf a polyatomic ion appears in in both reactant and product, treat it as a single unit.Balance oxygen and hydrogen last.Don’t forget diatomic molecules.Count your atoms as a check
13 Chemical StatesThe state of the chemicals is important to the chemical reaction.State can be added by putting an abbreviation in parentheses after each chemical.StateAbbreviationExampleSolid(s)NaCl(s)Liquid(l)H2O(l)Gas(g)H2(g), O2(g)Aqueous(aq)NaCl(aq) (in water)
14 Water: Final Balanced Equation Hydrogen and Oxygen are both gasesWater is a liquidFinal balanced equation with the states of all components is:2H2(g) + O2(g) 2H2O(l)You will not be required to give the states for an equation
15 Resources - Links Khan Academy Balancing Equations pHET Balancing AppletBalancing Complex Equations with the Table Method Video
16 Resources – Table Example Step 1: Start with an unbalanced equation
17 Resources – Table Example Step 2: Draw boxes around all the chemical formulas
18 Resources – Table Example Step 3: Make an element inventoryBefore = ReactantAfter = Product
19 Resources – Table Example Step 4a: Balance the Equation and the InventoryBefore = ReactantAfter = Product
20 Resources – Table Example Step 4b: Final Steps…Before = ReactantAfter = Product
21 Resources – Extra Practice The following are Word Based Balancing ProblemsPage 137: Q14Page139: Q22, Q23, Q26