Chemical Formulas and Equations p Vocabulary 1. chemical formula 2. chemical equation 3. reactant 4. product 5. law of conservation of mass

1. Chemical Formulas p. 32 A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance. A chemical formula shows how many atoms of each kind are present in a molecule.

mono – 1hexa - 6 di - 2hepta – 7 tri - 3octa - 8 tetra - 4nona - 9 penta - 5deca - 10 Prefixes Used in Chemical Names Prefixes tell you how many atoms of each element are in a compound.

Science humor… Name the following compound: Ba(Na) 2 Banana!!! Ha, Ha, Ha!!! Chemical Equations p A chemical equation is a representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products. 3. A reactant is a substance or molecule that participates in a chemical reaction 4. A product is the substance that forms in a chemical reaction. A chemical equation uses chemical symbols and formulas as a shortcut to describe a chemical reaction.

From Reactants to Products p. 34 The starting materials in a chemical reaction are the reactants. The substances formed from a reaction are the products.

The Importance of Accuracy p. 35 The symbol or formula for each substance in the equation must be written correctly. For a compound, use the correct chemical formula. For an element, use the proper chemical symbol.

The Reason Equations Must Be Balanced p. 35 Atoms are never lost or gained in a chemical reaction. They are just rearranged. Every atom in the reactants becomes part of the products. When writing a chemical equation, make sure the number of atoms of each element in the reactants equals the number of atoms of those elements in the products. This is called balancing the equation. Hmmm… I bet this is fun!!

The Law of Conservation of Mass p. 35 Balancing equations comes from the work of the French chemist, Antoinne Lavoiser. Lavoisser found that the total mass of the reactants was ALWAYS the same as the total mass of the products. The law states that mass is neither created or destroyed in ordinary chemical or physical changes. This law means that a chemical equation must show the same numbers and kinds of atoms on both sides of the arrow.

How to Balance an Equation p. 36 To balance an equation, you must use coefficients. A coefficient is a number that is placed in FRONT of a chemical symbol or formula. For example, 3CO 2 represents carbon dioxide molecules. The number 3 is the coefficient. The number 2 is the subscript For an equation to be balanced, all atoms must be counted. You multiply each subscript in the formula, in this case 2, by the formula’s coefficient, in this case 3. It means there would be 3 atoms of carbon for every 6 atoms of oxygen.

Quiz Time! 1. What is the difference between reactants and products in a chemical reaction? Reactants are the starting substances and products are the substances that are formed as a result of a chemical reaction. Calculating Numbers of Elements and Atoms 2. DDT = C 14 H 9 Cl 5 Elements =3Atoms = Ascorbic acid = C 6 H 8 O 6 Elements =3 Atoms =20 4. Nitroglycerin = C 3 H 5 N 3 O 9 Elements =4 Atoms =20 5. Rubbing Alcohol = C 3 H 8 O Elements =3 Atoms = 12

6. If you see 4O 2 in an equation, what is the coefficient? 4 7. What is the difference between the formula CO 2 and the symbol Co? CO 2 is the formula for carbon dioxide. Co is the symbol for cobalt. More Science Humor… 8. What does a doctor do with an injured chemist? Helium 9. What does a doctor do with a sick chemist? Curium 10. What happens if the doctor can’t cure him or her? Barium