2. Building Science Champions

3.  Describe the information conveyed in a chemical equation.  Apply the principle of conservation of mass to chemical reactions.  Identify and describe three classes of chemical reactions.

4.  Chemical equation  Subscript  Reactant  Product  Conservation of mass  Coefficient  Synthesis  Decomposition  Replacement

5.  Chemical Equations are short, easy ways to show a chemical reaction by using elements’ symbols instead of words.  Symbols are easy to understand.

6.  The formula will show the ratio of elements in a compound.  C 12 H 22 O 11 is the chemical formula for sugar.  The letter corresponds to a particular element on the periodic table.  The subscript corresponds to the element that precedes the subscript.  If there is no subscript after a letter then there is one (1) of that particular element.  CO 2

7.  A chemical equation summarizes a chemical reaction.  The material you begin with is the REACTANT.  The completed reaction is the PRODUCT. Reactant + Reactant Product + Product = YIELDS

8.  When there are two or more reactants they are separated by a plus sign.  When there are two or more products they are separated by a plus sign.  The ratio of products to reactant can change. Reactant + Reactant Product Reactant Product + Product Reactant + Reactant + Reactant Product

9.  Regardless of the total number of reactants and products involved, all the atoms at the start of the reaction have to be present at the end of the reaction.  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 product.

10.  The law of conservation states: ▪ “Matter cannot be created nor destroyed during a chemical reaction.”

11.  Chemical equations are short hand for chemical reactions.  Subscripts go to the element before them.  To the left of the yield signs are reactants and to the right are products.  There can be multiple products and reactants.  Matter cannot be created nor destroyed.

12.  How do masses of the atoms in the reactants of a chemical reaction compare with the atoms in the products?  The number of atoms remain equal and the total of mass is unchanged.

13.  A chemical reaction must show the same number of each type of atom on both sides of the equation.  When this happens the equation is BALANCED.

14.  H 2 + O 2 H 2 O  Does the left side equal the right side?  2 Hydrogen and 2 Oxygen on the left  2 Hydrogen and 1 Oxygen on the right  Not equal. So what can be done to balance the equation?

15.  Add a coefficient of 2 in front of the H 2 O  Coefficient is the number placed in front of chemical formulas in an equation.  A coefficient tells how many atoms or molecules there are.  The coefficient is factored out until the next sign.  H 2 + O 2 2H 2 O  Left side – 2 Hydrogen and 2 Oxygen  Right side – 4 hydrogen and 2 Oxygen  How can we balance them out?

16.  Place a 2 in front of the H 2 in the reactant.  2H 2 + O 2  2H 2 O  Left side – 4 Hydrogen and 2 Oxygen  Right side – 4 Hydrogen and 2 Oxygen  We are balanced!!!!!!!!!!!!!!!!!

17.  Left side – 1 Magnesium and 2 Oxygen  Right Side – 1 Magnesium and 1 Oxygen  Is the equation balanced?  Now what?  Add 2 in front of Magnesium in the reactant and Magnesium in the product. 2Mg + O2 2MgO  Are we balanced?

18.  C + Cl2 CCl4  C + 2 Cl2CCl4  Al2O3 Al + O2  2 Al2O34 Al + 3 O2  ***You can only change coefficients you CANNOT change subscripts. ***

19.  There are 3 major classifications of chemical reactions:  Synthesis  Decomposition  Replacement

20.  When two or more substances combine to make a more complex substance the process is called synthesis.  Put things together.  Simple + Simple Complex  More reactants than products 2 SO 2 + O 2 + 2 H 2 O2 H 2 SO 4 Sulfur dioxide + Oxygen + water yields sulfuric acid

21.  Decomposition breaks down reactants into smaller products.  Complex Simple + Simple  More products than reactants 2 H2O2 2 H2O + O2 Hydrogen peroxide yields water and oxygen gas

22.  When one element replaces another in a compound, or when 2 elements in different compound trade places, this is replacement.  Reactant + Reactant Product + Product CaCO 3 + 2 HCl CaCl 2 + H 2 O 3 2 CuO + C2 Cu + CO 2

23.  Chemical equations show chemical reactions  Matter cannot be created nor destroyed  Three types of chemical reactions  Synthesis  Decomposition  Replacement

24.  Anderson, M. et all (2012) Physical Science. McGraw-Hill: Columbus  Frank, D.V et al (2001). Physical Science. Prentice Hall: New Jersey