Chemistry: Writing & Balancing Chemical Equations

Def: Chemical Reaction → when matter combines or breaks apart to produce new kinds of matter with different properties

Four Evidences of a Chemical Reaction:

• Color Change

• Release of a gas

• Precipitate → solid that forms from solutions being combined

• Change in heat or light

Def: Reactants → starting substances (written on the left)

Def: Products → the finishing substances (written on the right)

Important Note: when writing and balancing, the equation must have the same number and type of each element on both sides of the chemical reaction

Symbols:

• ¨+¨ → add to; reacts with; mixed with

• ¨→¨ → yields; produces; forms

• (s) → solid; (l) → liquid; (g) → gas; (aq) → aqueous

• arrow with a triangle above → heat was added

• arrow with a formula above → catalyst (a substance that speeds up the rate of a reaction without being used up in the reaction by lowering activation energy)

• two half arrows facing opposite directions → reaction of reversable

• Î → gas was released

• down arrow → precipitate was formed

• NR → no reaction took place

Diatomics → Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine

Types of Reactions:

• Combination Reaction: element + element → compound

• Decomposition Reaction: 1 reactant → 2 or more products

• Single Replacement Reaction: element + compound → compound + element

  • Activity Series Chart

  • If the element is higher than the cation, then it will replace it. If not, no reaction

• Double Replacement Reaction: 2 reactants + 2 compounds → 2 products + 2 compounds (precipitation reaction)

• Combustion Reaction: same products. CH4 + 2O2 → CO2 + 2H2O

Acids:

• Hydrochloric → HCl

• Sulfuric → H2SO4

• Phosphoric → H3PO4

• Nitric → NHO3

Write & Balance Reactions:

• Write the formula for reactants to the left, the formula for product to the right

• Balance equation using coefficients (number in front of formula)

  • When balancing, do hydrogen and oxygen last

Other Types of Reactions:

• Exothermic: exo- → out; releasing heat; reactions have more energy than products (combustion reaction)

• Endothermic: endo- → takes in; absorbs energy; products have more energy than reactions