1. Chemical Equations Putting chemical changes into words

2. A chemical equation is a symbolic representation of a chemical reaction.

3. Equation Example: The burning of methane gas in oxygen is: CH 4 + 2 O 2 → CO 2 + 2 H 2 O

4. Review: Element Symbols  All elements are represented by a 1 or 2 letter symbol For example For example C = Carbon C = Carbon Ne = Neon Ne = Neon O = Oxygen O = Oxygen  The symbols are shown on the periodic table

5. Chemical Formulas  Shows the elements & number of atoms of each element in a molecule  H 2 SO 4 Elements Elements Hydrogen; 2 atoms Hydrogen; 2 atoms Sulfur: 1 atom Sulfur: 1 atom Oxygen: 4 atoms Oxygen: 4 atoms 7 atoms total 7 atoms total Subscript

6. Coefficients  A chemical formula may begin with a number.  If there is no number, then “1” is understood to be in front of the formula. This number is called the coefficient. This number is called the coefficient.

7. Coefficients The coefficient represents the number of molecules of that compound or atom needed in the reaction. The coefficient represents the number of molecules of that compound or atom needed in the reaction. For example: For example: 2H 2 SO 4 – 2 molecules of Sulfuric Acid2H 2 SO 4 – 2 molecules of Sulfuric Acid

8. Coefficients  2H 2 SO 4 – 2 molecules of Sulfuric Acid A coefficient is distributed to ALL elements in a compound A coefficient is distributed to ALL elements in a compound 2 – H 2 (for a total of 4 H atoms)2 – H 2 (for a total of 4 H atoms) 2 – S (for a total of 2 S atoms)2 – S (for a total of 2 S atoms) 2 – O 4 (for a total of 8 O atoms)2 – O 4 (for a total of 8 O atoms)

9. Reading Chemical Equations  Each side of an equation represents a combination of chemicals.  The combination is written as a set of chemical formulas, separated by + symbols. CH 4 + 2 O 2 → CO 2 + 2 H 2 O Coefficient

10. Reading Chemical Equations  The two sides of the equation are separated by an arrow. The combination of chemicals before the reaction are on the left side of the arrow, called the reactants The combination of chemicals before the reaction are on the left side of the arrow, called the reactants The right side indicates the combination of chemicals after the reaction, called the product. The right side indicates the combination of chemicals after the reaction, called the product.

11. For Example:  In this reaction, sodium (Na) and oxygen (O 2 ) react to make a single molecule, Na 2 O  The reactant in this equation are  The reactant in this equation are Na + O 2  The product in this equation is  The product in this equation is Na 2 O Na + O 2 → Na 2 O

12. Conservation of Mass  During any chemical reaction, the mass of the products is always equal to the mass of the reactants.  All the mass can be accounted for: Burning of wood results in products that appear to have less mass as ashes; where is the rest? Gases and smoke. Burning of wood results in products that appear to have less mass as ashes; where is the rest? Gases and smoke.  Law of conservation of mass

13. Balancing Equations  The Law of Conservation of Mass states that in a chemical reaction, the quantity or amount of each element does not change.  This means that each side of the equation must represent the same quantity of each element; in other words have the same number of each kind of atom

14. Balancing Equations Na + O 2 → Na 2 O  ReactantsProducts  Na 1 Na 2  O 2 O 1 In order for this equation to be balanced, there must be equal amount of Na on the left hand side and on the right hand side.

15. Balancing Equations Na + O 2 → Na 2 O Right now, there is 1 Na atom on the left but 2 Na atoms on the right. We solve this problem by putting a 2 in front of the Na on the left hand side, Like this: 2Na + O 2 → Na 2 O

16. Balancing Equations 2Na + O 2 → Na 2 O  ReactantsProducts  Na 2 Na 2  O 2 O 1

17. Balancing Equations 2Na + O 2 → Na 2 O  There are 2 Na's on the left and 2 Na's on the right. But what about the O?  We now must check to see if the O's are balanced on both sides of the equation.  On the left hand side there are 2 O's and the right hand side only has one. This is still an unbalanced equation.

18. Balancing Equations 2Na + O 2 → Na 2 O  To fix this we must put a coefficient of 2 in front of the Na 2 O on the right hand side. Now our equation reads: 2Na + O 2 → 2Na 2 O

19. ReactantsProducts Na 2Na 4 O 2 O 2  Notice that the 2 on the right hand side is "distributed" to both the Na 2 and the O.  Currently the left hand side of the equation has 2 Na's and 2 O's.  The right hand side has 4 Na's total and 2 O's.

20. Balancing Equations 2Na + O 2 → 2Na 2 O Again, this is a problem, there must be an equal amount of each chemical on both sides. To fix this let's add 2 more Na's on the left side. The equation will now look like this: 4Na + O 2 → 2Na 2 O

21.  Is this balanced? ReactantsProducts Na 4 Na 4 O2 O2 Same number of each atom on each side of the equation- YES IT IS BALANCED

22. Practice  http://phet.colorado.edu/en/simulation/bala ncing-chemical-equations http://phet.colorado.edu/en/simulation/bala ncing-chemical-equations http://phet.colorado.edu/en/simulation/bala ncing-chemical-equations  Khan academy  http://www.youtube.com/watch?v=RnGu3x O2h74 http://www.youtube.com/watch?v=RnGu3x O2h74 http://www.youtube.com/watch?v=RnGu3x O2h74

23. Plants make chlorophyll in the plants leaves.

24. The color changes in autumn leaves are due, in part, to the ending of a chemical reaction. The plants stop making chlorophyll while existing chlorophyll is breaking down. The brilliant colors of fall foliage result when green chlorophyll in leaves breaks down. The colors of other substances in the leaves become visible.

25. The copper-covered Statue of Liberty has stood in upper New York Bay for more than a 100 years. The green color of the Statue of Liberty comes from a change to the statues copper metal covering. These changes are a result from chemical reactions.

26. Matter changes whenever energy is added or taken away. In every physical and chemical change, the total amount of energy stays the same. This principle is called the Law of Conservation of Energy.

27. Sources http://en.wikipedia.org/wiki/Chemi cal_equations http://en.wikipedia.org/wiki/Chemi cal_equations

28. Chemical Reactions are…  When one or more substances are changed into new substances.  Reactants- the stuff you start with  Products- what you make

29.  The products will have NEW PROPERTIES different from the reactants you started with  Arrow points from the reactants to the new products