Chemical Equations Is a chemical reaction that is written using chemical formulas Can also be written in words Vinegar + Baking Sodium + Water + Carbon Soda acetate dioxide HC 2 H 3 O 2 + NaHCO 3 NaC 2 H 3 O 2 + H 2 O + CO 2 Video

Chemical Reaction Substances (elements or compounds) that are separated or combined to form new substances –Bonds are being broken or formed

REACTANTS “Ingredients” What you start with These exist before the chemical reaction begins On the left side of the arrow

Chemical Equations 2H 2 + O 2 2H 2 0 Reactants Produces Products (Reaction) (Stuff before the reaction) (Stuff after the reaction) Video Yields

PRODUCT The finished product “End result” The result of a chemical reaction The new substance(s) that is formed On the right side of the arrow

Chemical Equations 2H 2 + O 2 2H 2 0 Reactants Produces Products (Reaction) (Stuff before the reaction) (Stuff after the reaction) Video Yields

Chemical Equations 2H 2 + O 2 2H 2 O Coefficient: Subscript: The little number attached to the lower right of the symbol that tells us the number of atoms for that element. If there is NO subscript, then there is only one atom of that element in the compound. Big number in front, identifies the number of molecules. (Multiply this number by the subscript)

Chemical Equations Chemical name vs. Common name –Many chemicals have common household names. –In chemical equations their chemical name is used. EX. (the reaction between baking soda and vinegar) HC 2 H 3 O 2 (liquid) + NaHCO 3 (solid)  NaC 2 H 3 O 2 (solid) + H 2 O (liquid) + CO 2 (gas) Sodium hydrogen carbonate + acetic acid  Sodium acetate + Water + Carbon Dioxide

Law of Conservation of Mass matter cannot be created or destroyed Atoms can only be re-arranged. (Atoms in the reactants = Atoms in the product) EX: Think about classes in school, same # of students and teachers, they are just arranged different based on the period

So… The chemical equation must be balanced. Balanced Equation: The number of atoms in each element MUST be the same on the Reactant side as the Product side Reactants Products

Is the Equation Balanced? Lets try a few to see…

Flow Map Create a flow map of the steps to check if a chemical equation is balanced or unbalanced.

Step 1 Draw a line to separate the reactants from the products C + O 2 CO 2

Step 2 List the elements on each side of the equation C + O 2 CO 2 COCO COCO

Step 3 List the number of atoms for each element on both sides. (subscript only applies to symbol it is attached after, if there is a coefficient the number stops at the arrow or a plus sign) C + O 2 CO 2 COCO COCO =1 =2 =1 =2

Step 4 See if the number of atoms of each element are equal on both sides of the equation. C + O 2 CO 2 COCO COCO =1 =2 =1 =2

Example 2 2H 2 O 2H 2 + O 2 HOHO HOHO =4 =2 =4 =2

Now you try: 1.2H 2 O 2H 2 + O 2 2.2Na + 2H 2 O 2NaOH + H 2 3.CH 4 + O 2 CO 2 + H 2 O 4.CH 4 + 2O 2 CO 2 + 2H 2 O 5.3Fe 2 O 3 + CO 2Fe 3 O 4 + CO 2 6.2HCl + CaCO 3  CaCl 2 + H 2 O + CO 2

Now you try: 1.2H 2 O 2H 2 + O 2 2.2Na + 2H 2 O 2NaOH + H 2 3.CH 4 + O 2 CO 2 + H 2 O 4.CH 4 + 2O 2 CO 2 + 2H 2 O 5.3Fe 2 O 3 + CO 2Fe 3 O 4 + CO 2 6.2HCl + CaCO 3  CaCl 2 + H 2 O + CO 2

Summary Statement Explain why equations must be balanced and relate it to the law conservation of mass. Be prepared to share

Balancing Act Atoms are not CREATED or DESTROYED during a chemical reaction. Scientists know that there must be the SAME number of atoms on each SIDE of the EQUATION. To balance the chemical equation, you must add COEFFICIENTS in front of the chemical formulas in the equation. You cannot ADD or CHANGE subscripts!

How many Atoms in the Formula? 1. H 4 H – 4 2. H 2 O H – 2 O – 1 3. C 6 H 12 O 6 C – 6 H – 12 O – Fe 4 Fe NaCl Na - 6 Cl Fe 4 O 3 Fe - 12 O - 9

Chemical Reactions and Energy Chemical reactions always involve energy changes. Making and breaking bonds involves energy changes

Energy in Chemical Reactions Endothermic Reaction: reaction that absorbs energy (endo – go in) Feels cold Exothermic Reaction: reaction that releases energy in the form of heat (exo- go out) Feels hot

Section 1 Review pg Are the following chemical equations balanced? Why or why not? a. Ca + Cl  CaCl b. Zn + Ag S  ZnS + Ag c. Cl + NaBr  NaCl + Br 2.What evidence might tell you that a chemical reaction has occurred? 3.What is the difference between an exothermic and an endothermic reaction? 4.What forms of energy might be needed for a chemical reaction to take place?