Chemical Reactions

Nature of Reactions A chemical reaction is when you create a new substance with unique physical and chemical properties.

Reaction Representation Chemists use symbols to represent what happens in a chemical reaction. This representation is called a chemical equation. Na + Cl 2  NaCl

Parts of an Equation Reactants –What is going into the equation. Products –What is coming out of the equation. Law of Conservation of Mass Atoms cannot be created or destroyed. The mass of the reactants entering the equation must equal the mass of the products exiting the equation. “What goes in, must come out!!”

Parts of an Equation Arrow  –“yields” (“creates”, “produces”, “equals”) Subscript –The little number after the element that tells how many of each element is present. H 2 OZnCl 2 Al 2 O 3 Valence Charge (aka…oxidation number) –The charge represented in the chemical equation to represent how the element will react with the other reactants.

Parts of an Equation Coefficient –The big number written before the elements when balancing the chemical equations. 2HCl3Al 2 S 3 Representation of Gases –(diatomic elements) Gases are always written with a subscript of 2 when they are alone in the equation H 2 O 2 N 2 Cl 2 F 2

Parts of an Equation Example of the parts: 2Al S -2  Al 2 S 3 Coefficient Reactants Valence Charge Products Yields Subscripts

Label the Parts 2Ag +1 I -1 + Mg +2 Cl 2 -1  2AgCl + MgI 2 Label Each of these in the above equation. 1.Coefficients = Square 2.Valence Charge = Triangle 3.Subscripts = Circle 4.Reactants = One Underline 5.Products = Two Underlines 6.Yields = Sunshine

Balancing Equations Due to the law of conservation of mass.. –“what goes in, must come out” of an equation. In order to have the same number of atoms of each element that you started with…you must add coefficients. (big #s) You will place the coefficient in front of the symbol and will multiply by the subscripts.

Remember 2Al 2 O 3 Coefficient Subscripts Coefficients will multiply by the subscripts….2x2….2x3

Let’s Practice Counting Atoms

Let’s Try Balancing Equations 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 a the equation. To balance the chemical equation, you must add coefficients to the different parts of the equation.