Unit 4 – Chemical Equations & Reactions Conceptual Chemistry Unit 4 – Chemical Equations & Reactions

Objective 1 Read and express information given in chemical formulas.

Chemical Formula Shows the type and number of atoms present in a substance.

Chemical Formula In the chemical formula, subscripts show how many atoms are in the compound. C6H10N2O2 C = 6 H= 10 N= 2 O= 2

Chemical Formula The large numbers in front of the chemical formula, called coefficients, show the number of particles. 3C6H10N2O2 C6H10N2O2 = 3 total

Practice Problems: How atoms of each element are in the following? AlCl3 4 H2O 10 Fe3P2 6 Zn(NO3)2 Al2(SO3)3

Objective 2 Balance chemical equations.

Chemical Equation Reactants  Products Ex: 2 KClO3  2 KCl + 3 O2 Reactant = KClO3 Products = KCl + O2

Symbols (s) = (l) = (g) = (aq) = + =  = ∆ = H2 (subscripts) =   (l) = (g) = (aq) = + =  = ∆ = H2 (subscripts) = 2 H2 = (Coefficients) =

Balancing Equations The law of conservation of mass states that matter cannot be created or destroyed. The number of atoms reacting must equal the number of atoms produced. A chemical change rearranges these atoms into new substances.

To balance equations, follow these steps: 1. Count atoms on each side of the arrow. They should be equal. If not, you need to balance them. 2. Balance both sides by using coefficients. (They multiply through everything inside of that compound.) NEVER change subscripts! 3. Double check work.

Practice Problems ____ KClO3  ____ KCl + ____ O2 ____AlBr3 + ____ K2SO4  ____ KBr + ____ Al2(SO4)3 ____ C3H8 + ____ O2  ____ CO2 + ____ H2O

Objective 3 Describe chemical reactions and calculate percent yield.

Percent Yield Used to determine completeness of a reaction Actual Yield: actual amount of products produced in an experiment Theoretical Yield: maximum amount of products predicted from conservation of mass Percent Yield = Actual Yield x 100% Theoretical Yield

Practice Problem When a measured amount of hydrogen gas reacted with a measured amount of oxygen gas, 2.5 g of water was produced. The expected amount was 3.0 g. What was the percent yield?