CHEMICAL REACTIONS

CHEMICAL CHANGES When bonds break and new bonds form. Chemical changes are also called chemical REACTIONS.

WRITING CHEMICAL REACTIONS A chemical equation is a written version of a chemical reaction. Chemical equations are written from left to right (just like math equations) An arrow is used in place of the equals sign and means “is changed to,” “yields,” or “becomes” Starting Materials  Ending Materials

REACTANTS One or more substances that START the reaction. Written on the LEFT side of the arrow.

PRODUCTS One or more substances that END the reaction. Written on the RIGHT side of the arrow.

2H 2 + O 2  2H 2 O Circle the REACTANTS. Draw a square around the PRODUCTS Product is 2H 2 O Reactants are 2H 2 and O 2

LAW OF CONSERVATION OF MATTER Matter cannot be created or lost, just rearranged The amount of products will ALWAYS equal the amount of reactants. If you start with 10 grams of reactants, you will end up with 10 grams of products.

Types of Reactions There are THREE different types of reactions: Synthesis Decomposition Replacement

Synthesis Reactions Synthesis means to put things together. In a synthesis reaction you begin with two or more reactants and end with one product. A + B  C Example: 2H 2 + O 2  2H 2 O

Decomposition Reaction In a decomposition reaction, one reactant breaks down into simpler products. You begin with one reactant and end up with two or more products A  B + C Example: 2H 2 O 2  2H 2 + O 2

Replacement Reaction In a replacement reaction, one element trades places with another element. AB + C  A + BC Example: 2CuO + C  4Cu + CO 2

What type of reaction? C+ O > CO 2 2Ag 2 O ----> 4Ag + O 2 CaO + H 2 O ----> Ca(OH) 2 Zn + H 2 SO > ZnSO 4 + H 2

GOT BALANCE?? Mg + O 2  MgO Na + O  Na 2 O Sn + Cl 2  SnCl 2 If a reaction is not balanced, YOU have to balance it!!!

BALANCING EQUATIONS STEP #1: Pick an element. (save H’s and O’s for last!) STEP #2: Count the number of atoms of that element on both sides of the arrow. STEP #3: If they are equal, go back to Step #1 and pick another element.

BALANCING EQUATIONS STEP #3 (Part 2): If numbers of atoms are NOT equal, place COEFFICIENTS into the equation to make them equal. (REMEMBER THAT COEFFICIENTS ARE THE BIG NUMBERS!!!) STEP #4: Repeat all of the steps for all elements STEP #5: Check your final equation.

C 2 + O 2  CO 3 Is this equation balanced or unbalanced? This equation is unbalanced There are 2 Carbons in the reactants, and only one in the products. There are 2 Oxygens in the reactants and 3 in the products.