Warm-Up Nov.7,2013 What are the clues that a chemical reaction has occurred? Remember: Write your name, block #, the date, the question, and your answer. Look to your notes if you can’t remember the format!!!

1. A gas bubbles off. 2

2. A new solid material is formed (a precipitate.) 3

3. Color change. 4

4. Heat and/or light are emitted. 5

Law of Conservation of Mass & Balancing Chemical Equations

Objectives Objectives 8.P.1.4 Explain how the idea of atoms and a balanced chemical equation support the law of conservation of mass. Student Friendly Objective:   I can use diagrams to model chemical reactions.   I can explain the Law of Conservation of Mass.   I can explain how chemical reactions are represented so that mass is conserved.   I can balance chemical equations and explain why they are balanced

Vocabulary Subscript Vs Coefficient Subscript Vs Coefficient Reactant Vs Product Reactant Vs Product Atom Vs Molecule Atom Vs Molecule Law of Conservation of Mass Law of Conservation of Mass Word Equation Word Equation Skeleton Equation Skeleton Equation Balanced equation Balanced equation

Subscripts C 12 H 22 O 11 C 12 H 22 O 11 There are 12 atoms of Carbon There are 12 atoms of Carbon There are 22 atoms of Hydrogen There are 22 atoms of Hydrogen There are 11 atoms of Oxygen There are 11 atoms of Oxygen If there is not a subscript listed, it is understood to be 1. If there is not a subscript listed, it is understood to be 1. Example: NaCl Example: NaCl There is one atom of Sodium There is one atom of Sodium There is one atom of Chlorine There is one atom of Chlorine

You Practice! NaHCO 3 Sodium – 1 Hydrogen – 1 Carbon – 1 Oxygen -3 HCl Hydrogen – 1 Chlorine - 1

Coefficient 2H 2 SO 4 This means there are 2 compounds of Sulfuric Acid. Think: H 2 SO 4 H 2 SO 4 Counting the atoms: Hydrogen – 4 Sulfur – 2 Oxygen - 8

You Practice!! 3H 3 PO 4 Hydrogen – 9 Phosphorus – 3 Oxygen H 2 O Hydrogen – 4 Oxygen - 2

Chemical Equations Chemical equations express what is happening in a chemical reaction using symbols. 2K + Cl 2 2KCl 2K + Cl 2 2KCl Reactant Product Reactant Product yields

Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. Law of Conservation of Matter Law of Conservation of Matter The Law of Conservation of MatterLaw of Conservation of Matter Kotz web ChemicalFactory 100% 80% 20%

The key to chemical reactions! The Law of Conservation of Mass In a chemical reaction, no atoms are created or destroyed. The atoms in the reacting molecules simply re-arrange to form new molecules. Mass is “conserved.” 16

Balancing Equations The mass of the reactants must equal the mass of the products The mass of the reactants must equal the mass of the products Or the number and type of atoms in the reactants is equal to the number and type of atoms in the products Or the number and type of atoms in the reactants is equal to the number and type of atoms in the products

Balancing Equations ReactantsProducts H22 hydrogen + oxygen  water O 2 O 2  H2OH2OH2OH2O H 2 H 2 +O21

Balancing Equations H 2 + O 2  H 2 O 2 ReactantsProducts H22 O22 hydrogen + oxygen  hydrogen peroxide X YOU CANNOT CHANGE THE SUBSCRIPTS

Balancing Equations H 2 + O 2  H 2 O ReactantsProducts H22 O21 hydrogen + oxygen  water 2

Balancing Equations H 2 + O 2  H 2 O ReactantsProducts H24 O22 hydrogen + oxygen  water 2

Balancing Equations 2 H 2 + O 2  H 2 O ReactantsProducts H44 O22 hydrogen + oxygen  water 2 (g) (l)

Chemical Equations Reactants – the substances that exist before a chemical change (or reaction) takes place. Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

CH O 2  CO H 2 O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

Cl H H H HH H H H 2 + Cl 2  HCl H 2 + Cl 2  2 HCl reactants products H Cl reactants products H Cl (unbalanced) (balanced) Unbalanced and Balanced Equations

Practice… ___N 2 + ___H 2  ___NH 3 N = N = H = H = ___C 2 H 6 + ___O 2  ___CO 2 +___H 2 O C =C= H = H = O = O =

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What does H look like? What does H look like? What does H 2 look like? What does H 2 look like? What does 2H look like? What does 2H look like? What does 2H 2 look like? What does 2H 2 look like? H H H HH H H H H

What does CH 3 look like? What does CH 3 look like? What does 3CH look like? What does 3CH look like? What does 2C + 2H look like? What does 2C + 2H look like? What does C 2 + H 2 look like? What does C 2 + H 2 look like? What does 2CH 3 look like? What does 2CH 3 look like? CHH H HH H C C C CHH H C HH H C C H H + HH C C +