Unit 4 Chemical Equations Counting Atoms Counting Atoms

Unit 4: Chemical Equations Counting Atoms

Counting Atoms H 2 O subscript How many H? How many O? Subscripts only apply to the atom that they immediately follow.

Counting Atoms If elements or compounds are inside of parentheses, then the subscript that follows the parentheses applies to everything inside (just like in math class). Ba(OH)2 Atoms of Barium: Atoms of Oxygen: Atoms of Hydrogen:

Counting Atoms Practice Ca 3(PO 4)2 Atoms of Calcium: Atoms of Phosphorus: Atoms of Oxygen: Al 2(SO 4)3 Atoms of Aluminum: Atoms of Sulfur: Atoms of Oxygen:

Unit 4: Chemical Equations Balancing Equations

Balancing Equations Remember the law of conservation of mass? • When a chemical reaction occurs, no atoms are created or destroyed – they are just rearranged • Amount of each element on the left side (reactants) must equal the amount of the same element on the right side (products) reactants products

Balancing Equations – The Steps! 1. Put coefficients in front of each substance to get the quantities on the left side = the right side 2. 2 Na + Cl 2 2 Na. Cl Ø Use the smallest whole number coefficients possible.

1. 2. 3. 4. Balancing Equations - Hints Start with one of each reactant and product. Save hydrogen for 2 nd to last. Save oxygen for last. Diatomic elements: HOFBr. INCl (only when alone) Example: hydrogen gas is written H 2 5. Phases: • Solid = (s) • Liquid = (l) • Gas = (g) • Aqueous (dissolved in water or solution) = (aq)

Balancing Equations Example #1 Now let’s balance this equation… __C 3 H 8 (g) + __O 2 (g) __CO 2 (g) + __H 2 O (l)

Balancing Equations Practice #1 Balance the following chemical equation: __Pb. S 2 (s) + __O 2 (g) __Pb. O 2 (s) + __SO 2 (g)