Chemical Reactions – Part 1 Balancing Chemical Equations

Lesson Essential Question… How do I balance a chemical equation?

Parts of a Chemical Reaction 2 NaCl (aq) + Ag 2 SO 4(aq) Na 2 SO 4(aq) + 2 AgCl (s) Reactants??? Products??? Yields??? States of matter at room temperature before reaction started. ??? State of matter after the reaction. Use solubility rules to determine state. ??? States of Matter (aq) – aqueous (s) – solid (ppt or solid) (l)- liquid (ex. H 2 0, Br 2 ) (g) – gas (ex. H 2, O 2 ) COEFFICIENTS These numbers are from balancing the equation. They are the number of “moles” of each compound indicating the ratio of each reactant to product formed.

Think back to the Law of Conservation of Matter What did it say? “No matter can be created nor destroyed in an ordinary chemical reaction.”

With that in mind… Evaluate the chemical reaction below. Does it support the Law of Conservation of Matter? H2H2 O2O2 H2OH2O H H O O H H O + Lets look at it on the molecular level. Lets look at hydrogen first. On the reactant side there are two hydrogen atoms. On the product side there are two hydrogen atoms. So far hydrogen is balanced. For oxygen: there are two oxygen atoms on the reactant side. On the product side there is one oxygen atom so another water molecule needs to be added to the product side. H H O Now there are four hydrogen atoms on the product side. Add another hydrogen molecule to the reactant side giving a total of four hydrogen atoms on the reactant side. H H The equation is now balanced according to the Law of Conservation of Matter so how do we show that with the chemical equation? COEFFICIENTS 2 2

Try Balancing this combustion reaction… CH 4 O2O2 CO 2 O O H H O + Lets look at it on the molecular level. Lets look at hydrogen first. On the reactant side there are four hydrogen atoms. On the product side there are two hydrogen atoms. So you need to add another water molecule. Now there are four oxygen atoms on the product side. Add another oxygen molecule to the reactant side giving a total of four oxygen atoms on the reactant side. The equation is now balanced according to the Law of Conservation of Matter so how do we show that with the chemical equation? COEFFICIENTS 2 2 H2OH2O+ H H H H C O O C H H O O O There is one carbon on the reactant side There is one carbon on the product side This symbol on top of the “yields” arrow indicates that heat or burning was involved.

Try Balancing These Equations… 1. Al + Fe 3 N 2 AlN + Fe 2. NaClO 3 NaCl + O 2 3. BF 3 + Li 2 SO 3 B 2 (SO 3 ) 3 + LIF 4. Sn(NO 2 ) 4 + Pt 3 N 4 Sn 3 N 4 + Pt(NO 2 ) 4 5. B 2 Br 6 + HNO 3 B(NO 3 ) 3 + HBr