Balancing and Chemical Formulas

1. Balancing and Chemical Formulas

2. What is a chemical equation? A representation of a chemical reaction using symbols of the elements to indicate the amount of substance, usually in moles, of each reactant and product.

3. Reading A Chemical Equation The two sides of the equation are separated by an arrow. • The combination of chemicals before the arrow is called the REACTANTS. • The combination of chemicals after the arrow is called the PRODUCTS. P4(aq)+ O2(g)  P2O5 (aq) Reactants Product

4. What are the little letters in parenthesis? H2CO3(aq) → H2O(l) + CO2(g) They indicate the states of matter of the reactants and products. • (g) for gaseous substances. • (s) for solids. • (l) for liquids. • (aq) for compounds in solution in water.

5. SnO2(s) + 2H2(g) Sn(s) + 2H2O(g) The Parts of a Chemical Equations • Label the following chemical equation: reactants products subscript coefficient state of matter yield sign

6. A Balanced Equation • Has equal numbers of atoms of each element in the reactants and in the products.

7. Why Do We Balance Equations? • The law of conservation of mass states that matter can neither be created or destroyed • Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction • the number of a particular atom is the same on both sides of a chemical equation

8. Law of Conservation of MassExamples Hydrogen gas and oxygen gas combine to create water. 2H2 + O2 2H2O • The large numbers, known as coefficients, indicate how many moles of each compound there are. This helps to satisfy the LCM! • They apply to every element in the compound (2H2O means 4 H’s & 2 O’s) • They are the coefficients should be in the lowest whole number ratio Particles are rearranged, not created or destroyed!

9. RULES TO BALANCE EQUATIONS • You cannot change subscripts: • Ex: H2O is water • H2O2 is hydrogen peroxide • These are not the same thing

10. How do you balance an equation? The only “tool” at your disposal in balancing equations is a “coefficient” • Whole number • Written to the left of a formula • Multiplies the number of atoms of each element present in the compound

11. How do you balance an equation? Coefficients act as a scalar (also called a multiplier) • Ex: 6H2O has 12 hydrogen and 6 oxygen • Ex: 3Al2(SO4)3 has 6 aluminum, 9 sulfur, and 36 oxygen Just remember that all the formulas in the initial equation are correct, the ONLY thing you can do to balance an equation is by adding COEFFICIENTS. AGAIN, you CAN NOT change the subscripts.

12. list the atoms that are involved on each side of the arrow Mg + O2MgO Lets start balancing… Chemical Equation: Mg + O2MgO Mg O Mg O

13. Mg + O2 MgO Mg + O2MgO Mg O Mg O 1 1 2 1 Then start balancing: [1] Just count up the atoms on each side 1 1 2 1 [2] The numbers aren’t balanced so then add “A COEFFICIENT” to make up for any shortages 2 2 2 And adjust totals

14. 2 1 2 Mg + O2MgO 2 2 Mg O But the numbers still aren’t equal, so add another “COEFFICIENT” 2 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE HAVE A Balanced EQUATION !!

15. Some pointers in balancing • Only balance one element at a time • Use a pencil • easier to change coefficients as needed • Leave oxygen for last • Leave hydrogen for second to last. • Keep polyatomic ions together if they are the same on both sides. Pb(NO3)2 + Na2S --> PbS + NaNO3

16. Let’s Practice ____NH3 + ____O2___NO + ___H2O ___KNO3+___H2CO3___K2CO3+___HNO3