Balancing Equations Section 7.3 in Textbook

Chemical Equations The substances involved in a chemical reaction before the change occurs are called the reactants The new substances formed after the change are called the products We say that reactants yield products

Using Equations to Represent Reactions Reactants  Products C(s) + O2(g)  CO2(g) “1 carbon reacts with 1 oxygen molecule yields 1 molecule of carbon dioxide” The letters behind the chemical indicates whether the substance is solid (s) or (cr), liquid (l), aqueous solution (aq), or gas (g).

Writing Chemical Equations A chemical equation is a shorthand for the expression of the reaction. For example: Hydrogen gas reacts with Oxygen gas to produce Dihydrogen monoxide. : can be written in shorthand as: H2 + O2  H2O

Conservation Obeyed In any chemical reaction, the conservation of mass is observed Principle of the conservation of mass states: matter can not be created or destroyed in a chemical reaction Therefore, the mass of the reactants and the mass products must be the same

Coefficients A numbers in front of compounds or elements in a chemical equation represent the number of particles in the reaction The coefficients are used to balance the equation to obey the law of conservation of mass H2 + O2  H2O 2 2

Balancing Equations Changing the subscripts changes the compound. When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts. Changing the subscripts changes the compound.

Steps to Balancing Equations There are four basic steps to balancing a chemical equation. 1.Write the correct formula 2.Find the number of atoms for each element on each side. 3.Determine where to place coefficients. 4.Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced)

Some Suggestions to Help You -Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last. -IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) -(Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units

Balancing Equations Keep track of the elements in a table, adjusting the amount of atoms as you put in coefficients You must go back and forth putting in coefficients until all of the atoms’ numbers are equal

Balancing Equations Practice 2.) Ca(NO3)2 + H2SO4  CaSO4 + HNO3

Balancing Equations Practice 3.) Fe + Cl2  FeCl3

Balancing Equations Practice 4.) Fe + O2  Fe2O3

Balancing Equations Practice 5.) Zn + HCl  ZnCl2 + H2

Balancing Equations Practice 6.) Cu + AgC2H3O2  Cu(C2H3O2)2 + Ag

Balancing Equations Practice *7.) H2O2  H2O + O2

Balancing Equations Practice *8.) Na + H2O  NaOH + H2

Balancing Equations Practice *9.) C2H6 + O2  CO2 + H2O

Balancing Equations Practice 10.) Fe + H2O  Fe3O4 + H2

Balancing Equations Practice 11.) Al2(SO4)3 + Ca(OH)2  Al(OH)3 + CaSO4