1. Conservation of Matter Mr. Luke’s Physical Science

2. Imagine:  After the beginning of 1 st period there are 500 students (take mass of all)  The teachers and students are atoms  Classrooms are molecules  Bell rings and you move to the next class (chemical reaction)  At the end of the reaction (class change), the same number of atoms exist, but the students and teachers are grouped together in different molecules/rooms.  Mass will remain constant through the reaction (same number of students and teachers).

3. Law of Conservation of Matter During a chemical reaction, matter is neither created nor destroyed. The total mass of the reactants must equal the total mass of the products.

4. Components of a Chemical Equation: Component:Definition: Element Symbol Chemical Formula Subscript Coefficient Coefficient x Subscript= # of atoms The letter or letters that represent an element. Ex: N, H, Pb A combination of symbols that represents the elements in a compound and their proportions. Ex: H 2 O, CO 2, NaCl A number in a chemical formula that tells the number of atoms in a molecule or the ratio of elements in a compound. Ex: CO 2 = 1C & 2 O A number in front of a chemical formula in an equation that indicates how many molecules of each reactant and product. Ex: 2 (H 2 O)

5. Examples: MoleculeFormulaElements# of atoms Hydrogen peroxideH2O2H2O2 1. 2. 1. 2. Natural gasCH 4 1. 2. 1. 2. Sugar C 12 H 22 O 11 1. 2. 3. 1. 2. 3. Element & Coefficient & Subscript = Chemical Formula = Chemical Equation (Reaction) Chemical equations are representations of chemical reactions!

6. Types of Reactions: ReactionsDefinition Synthesis (composition) Decomposition Replacement When two or more elements or compounds combine. The Cookie ( ingredients product) When compounds break down into simple products. Reverse Cookie (Product Ingredients) When one element replaces another in a compound. The Blender Cl 2 + 2KBr = 2KCl + Br 2

7. Steps to Balancing Equations:  1. Write the Equation Mg + O 2 MgO  2. Count the Atoms Mg + O 2 MgO 1 2 1 1  3. Use Coefficients to Balance the Atoms Mg + O 2 2 MgO 2 2 Mg + O 2 2 MgO 2 2 2 2  4. Look Back and Check

8. Showing that matter is CONSERVED!  2HCl + Zn H 2 + ZnCl 2 Replacement Balanced !

9. Practice: ReactantsProducts What type of Reaction?  A. ____ HgO ____ Hg + ____ O 2 ________________

10. Practice:

11. C. _____ NaCl (electricity ______ Na + _______ Cl 2 _____________

12. Hints:  Think Lowest Common Multiples  If there is an odd or you get stuck, double all coefficients  Look to balance the easy elements first  Look at balancing the oxygens  Add all the atoms of an element for each side of the equation