(c) S. Coates 2012

 Everything around us is made of atoms. These atoms are constantly interacting with each other.  We call those interactions chemical reactions, and they are happening EVERYWHERE. (c) S. Coates 2012

 Evidence for Chemical Reactions  Chemical reactions involve observable changes. Make a List: What are some OBSERVABLE CHANGES that take place while roasting marshmallows? (Think of the fire and the marshmallow) (c) S. Coates 2012

 Evidence for Chemical Reactions  The list you just came up with can be sorted into TWO lists… 1. Changes in Properties 2. Changes in Energy These are the TWO Main kinds of Observable Changes that take place in a chemical reaction. (c) S. Coates 2012

1. Changes in Properties include: Gases Produced Bubbles may appear in liquid Color Change Smell Change Solid may appear when 2 solutions are mixed (*THIS IS CALLED A PRECIPITATE) (c) S. Coates 2012

 Watch the video below and look for CHANGES IN PROPERTIES. CHANGES IN PROPERTIES (c) S. Coates 2012

1. Changes in Properties  Q: What change in property did the Diet Coke go through during the chemical reaction in the video?  A: Increased “fizziness” or CO 2 was the most observable change. (c) S. Coates 2012

 For example, sometimes TWO liquids will mix together and will form a SOLID. We call this solid a PRECIPITATE. We call this solid a PRECIPITATE (c) S. Coates 2012

2. Changes in Energy: Some reactions ABSORB energy Other reactions RELEASE energy You can usually tell if something is absorbing or releasing energy because there is a CHANGE IN TEMPERATURE. (c) S. Coates 2012

2. Changes in Energy: Reactions that ABSORB energy are called ENDOTHERMIC Reaction that RELEASE energy are called EXOTHERMIC (c) S. Coates 2012

 The BIGGEST observable characteristic of a chemical reaction is the production of NEW MATERIALS  The NEW MATERIALS will have properties that are different from those of the starting materials. (c) S. Coates 2012

 Chemical Reactions occur when chemical bonds break or when new bonds form! Magnesium Metal (Mg) Oxygen(O) Magnesium oxide (MgO) (c) S. Coates 2012

2. Changes in Energy  Chemical Reactions happen because of the way chemicals are stuck together or “bonded”.  Some bonds are strong and hard to change…think of Glass.  Some bonds are weak…think of Wood. (c) S. Coates 2012

 STOP AND REVIEW 1. What are some examples of evidence for a chemical reaction? 2. What two kinds of energy changes can take place during a chemical reaction? 3. What happens to the chemical bonds in a substance during a chemical reaction? 4. When a solid forms as two solutions are mixed together, what is that solid called? (c) S. Coates 2012

 Think about our class. We have a group of students and a teacher. (c) S. Coates 2012

 When the bell rings, you all leave and a new group of students comes in, and all of you go to a new class room. (c) S. Coates 2012

 The number of students and teachers in the school has not changed. But their arrangement is different and the new groups interact differently. (c) S. Coates 2012

 We use symbols when writing chemical reactions.  Using these symbols makes it easier and faster to read and write reactions.  How else do you use symbols as a short-cut in daily life? (c) S. Coates 2012

 A chemical equation is a shorter, easier way to show chemical reactions, using symbols instead of words.  These symbols come from the Periodic Table of the Elements. These one or two letter abbreviations are unique for each element (or type of atom). (c) S. Coates 2012

Use a Periodic Table to determine what each of these symbols stand for: Record the symbol and what it stands for. Au Fe Pb Al Ag Ca Sn C (c) S. Coates 2012

Au Fe Pb Al Ag Ca Sn C GoldLeadSilverTin Iron Aluminum Calcium Carbon (c) S. Coates 2012

 You have already seen many chemical formulas… H2OH2O  What does the “H” stand for?  What does the “O” stand for?  What does the little “2” stand for? Hydrogen Oxygen There are TWO hydrogen atoms (c) S. Coates 2012

Here are some familiar items. Use a Periodic Table of the Elements to record what these compounds are made of… CompoundFormula AspirinC9H8O4C9H8O4 BleachNaClO SugarC 12 H 22 O 11 RustFe 2 O 3 Rubbing AlcoholC3H8OC3H8O Lowercase “L”, not an I. (c) S. Coates 2012

CompoundFormulaMade of…. AspirinC9H8O4C9H8O4 9 Carbons, 8 Hydrogens, and 4 Oxygens BleachNaClO1 Sodium, 1 Chlorine, 1 Oxygen SugarC 12 H 22 O Carbons, 22 Hydrogens, and 11 Oxygens RustFe 2 O 3 2 Irons, 3 Oxygens Rubbing Alcohol C3H8OC3H8O3 Carbons, 8 Hydrogens, and 1 Oxygen (c) S. Coates 2012

 Structure of a chemical equation: Every chemical equation is written THE SAME WAY… Reactant + Reactant  Product + Product Sometimes there are more than 2 reactants. Sometimes there is only 1 reactant. Sometimes there are more than 2 products. Sometimes there is only 1 product. (c) S. Coates 2012

 See if you can answer the following questions for this chemical reaction : CaCO 3 CaO + CO 2 (Heated) 1.How many reactants are there? 2.What is/are the reactant(s)? 3.How many products are there? 4.What is/are the product(s)? (c) S. Coates 2012

CaCO 3 CaO + CO 2 *Notice that the atoms we began with are the same atoms we end with, just in a different order! (Heated) CaOC 3 OO 2 (c) S. Coates 2012

 The amount of matter involved in a chemical reaction does not change.  The total mass of the reactants MUST EQUAL the total mass of the products.  We call this principle Conservation of Mass. (c) S. Coates 2012

 How do you know if the mass of the products is equal to the mass of the reactants?  Subscript Numbers!  If you add up the NUMBER of EACH element on the reactant side and compare it to the NUMBER of the SAME element on the product side you can tell if the mass of the reactants is equal to the mass of the products. CaCO 3  CaO + CO 2 (c) S. Coates 2012

 For example: Na + Cl  NaCl 1. Count up the number of Na and Cl atoms on the reactant side. Na = 1Cl = 1 2. Count up the number of Na and Cl atoms on the product side. Na = 1Cl = 1 3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal. Yes! The masses are equal! (c) S. Coates 2012

 Here’s another: Fe 2 + S 2  Fe 2 S 2 1. Count up the number of Fe and S atoms on the reactant side. Fe = 2S = 2 2. Count up the number of Fe and S atoms on the product side. Fe = 2S = 2 3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal. Yes! The masses are equal! (c) S. Coates 2012

 But what if the numbers are NOT equal? H 2 + O 2  H 2 O 1. Count up the number of H and O atoms on the reactant side. H = 2O = 2 2. Count up the number of H and O atoms on the product side. H = 2O = 1 3. Compare the numbers. Are they the same? NO! The masses are NOT equal! That makes this equation “unbalanced” (c) S. Coates 2012

 Try another one… CO 2 + H 2 O  C 6 H 12 O 6 + O 2 1. Count up the number of C, H, and O atoms on the reactant side. C = 1H = 2O = 3 2. Count up the number of H and O atoms on the product side. C = 6H = 12O = 8 3. Compare the numbers. Are they the same? NO! The masses are NOT equal! That makes this equation “unbalanced” (c) S. Coates 2012

 What do you do when an equation is “unbalanced?”  That’s something you’ll be learning in high school Chemistry.  For now you just need to understand whether and equation is balanced or unbalanced. (c) S. Coates 2012

 Let’s summarize:  Chemical reactions can cause changes in properties and changes in energy.  Chemical reactions occur when the bonds between atoms break, or when new bonds between atoms are formed.  We can write equations for chemical reactions by using symbols  Chemical reactions must follow the Law of Conservation of Mass. (c) S. Coates 2012