The evaporation of a puddle of water Rust forming on a metal fence

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2 The evaporation of a puddle of water Rust forming on a metal fence

3 Recall that chemical changes occur when one substance rearranges itself to form a new substance A burning candle Toasting a marshmallow Iron rusts Silver tarnishes Chemical changes are also called CHEMICAL REACTIONS!

4 What evidence of a chemical reaction did we observe with the decomposition of glucose?

5 During a chemical reaction, matter (mass) cannot be created or destroyed! Law of Conservation of Matter Defined by Antoine Lavoisier in early 1700s Even though the matter may change from one form to another, the same number of atoms exists before and after the change takes place! All atoms present going in MUST COME OUT!

6 No matter is created or destroyed by such changes! The total amount of matter remains constant

7 The mass of the reactants the substances there before the reaction occurs must equal the mass of the product the substances there after the reaction takes place Mass of Reactants Mass of Products

8 Decomposition of HgO using heat

9 Chemical reactions are represented in chemistry by writing a chemical equation Reactants are shown on the left Products are shown on the right Arrow indicates direction of the chemical change and reads as yields or produces

10 Identify the product(s) and reactant(s) in the following reaction: Identify the product(s) and reactant(s) in the following reaction: water hydrogen + oxygen NiCl NaOH Ni(OH) 2 +2 NaCl

11 Iron Hard, gray-colored metal Rust Flaky, orange-red solid

12 This is written as: Iron + Oxygen Iron (III) Oxide

13 TAKE A LOOK AT THE NUMBERS Fe Fe Fe Fe O 2 O 2 O 2 Fe 2 O 3 Fe 2 O 3 How many Iron molecules? How many Oxygen molecules? What about the PRODUCT?

14 With iron (III) oxide, the MASS STAYS THE SAME! The total number of iron atoms and oxygen atoms in the reactants is the same as that in the product. The atoms were just rearranged! No new atoms were created and none were destroyed!

15 All atoms present in the reactants must be accounted for among the products! Same number of each type of atom on the product side as on the reactant side of the arrow Referred to as balancing the chemical equation

16 Subscripts Shows number of atoms in a compound Coefficients Number written in front of the chemical formulas (element symbols) in a balanced chemical equation Indicates relative numbers of reactants and products

17 3 H 2 SO 4 H S O Fe(NO 3 ) 3 + 3LiOH How many atoms of each type are represented by the following formulas? Fe N O Li H 2 NH 4 NO 3 + H 2 S N H O S 2 K + 2 H 2 O K H O

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19 So, let s look at the steps we need to take to BALANCE chemical equations: Let s work with the following equation: P + O 2 P 2 O 5 19

20 Step 1: Create a RAP table What s a RAP table?? It s a table that shows us: What atoms are present in the reaction How many atoms are present Are the atoms reactants or products?

21 P + O 2 P 2 O 5 #Reactant Atom #Product 1 P 2 2 O 5

22 Step 2: Go to the first atom that s not balanced and balance it! Since P atoms are not balanced, what do we need to do to balance it? Multiply it by 2! 2 x #Reactant Atom #Product 1 P 2 2 O 5

23 In step 2, we balanced the number of P atoms by multiplying the reactant side by 2 This now becomes the new coefficient in the chemical equation Modify the equation to reflect the change: 2P + O 2 P 2 O 5 #Reactant Atom #Product 2 P 2 2 O 5

24 Step 3: Move to the next unbalanced atom What is it? #Reactant Atom #Product 2 P 2 2 O 5 How can we balance the oxygen? Multiply reactants by 5 and products by 2 #Reactant Atom #Product 2 P 2 5 x 2 O 5 X 2

25 #Reactant Atom #Product 2 P 2 10 O 10 Adjust the chemical equation to reflect your changes: 2P + 5O 2 2 P 2 O 5 But notice that by changing oxygen, we also changed phosphorus! We need to go back and fix this!

26 Step 4: Write out the updated RAP table How can we balance the phosphorus? Multiply the # of reactant P atoms by 2! 2 x #Reactant Atom #Product 2 P 2 10 O 10

27 #Reactant Atom #Product 4 P 4 10 O 10 Adjust the chemical equation to reflect your changes: 4P + 5O 2 2 P 2 O 5 Do we have a balanced chemical equation now? Yes we do!

28 Look at this balanced chemical equation: 2AgNO 3 + MgCl 2 2AgCl + Mg(NO 3 ) 2 When an equation has polyatomics in it and the polyatomic appears on BOTH the reactant and product side of the equation, COUNT THE ENTIRE POLYATOMIC as an ATOM! So, the RAP table for the above equation would be: If the same polyatomic does not appear on both sides, break the polyatomic down into individual atoms! #R atom #P 2 Ag 2 2 NO Mg 1 2 Cl 2 28

29 Look at your chemical equation of the decomposition of glucose Write the chemical equation using formulas of each reactant and product Is the reaction balanced? How do you know? If not, BALANCE IT using coefficients!

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31 Learning to read a sentence or paragraph to extract out a chemical equation can be tough Follow these hints to be successful: Learn the diatomic gases HIGHLIGHT THEM ON YOUR PT! H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 Know the states of matter symbols Solid (s) Liquid (l) Gas (g) If you read the word solution, use the matter symbol (aq) Use your periodic table and pink ion sheet to correctly write the formulas of the compounds and elements from the names given Balance using coefficients AFTER ALL SUBSCRIPTS ARE CORRECT DO NOT ALTER THE CHEMICAL FORMULAS ONCE WRITTEN WITH CORRECT SUBSCRIPTS!

32 Read description of chemical reaction What are reactants, products, and their states (solid, liquid, gas, aqueous)? Write appropriate formulas using Periodic Table and Pink Sheet! Write the unbalanced equation that summarizes the above step

33 Make a RAP table Proceed element by element to determine what coefficients are necessary so that same number of each type of atom appears on both the reactant side and product side DO NOT CHANGE THE FORMULA OF ANY REACTANT OR PRODUCT! YOU CAN ONLY CHANGE COEFFICIENTS! Check to see that the coefficients are the smallest whole number that give the balanced equation

34 A solid piece of zinc reacts with hydrochloric acid to produce a solution of zinc chloride and hydrogen gas as the products