Reaction Types & Predicting Products

• List the five changes that are evidence a chemical reaction has occurred

• Color change — the substance changes color (e.g., iron rusting turns orange)
• Gas production — bubbles or fizzing appear (e.g., baking soda + vinegar)
• Precipitate forms — a solid appears in a liquid mixture
• Temperature change — the mixture gets noticeably hotter or colder
• Light or energy released — glowing, sparking, or flame

• What is the difference between reactants and products?

Reactants are the starting substances — they go on the left side of the arrow.
Products are the new substances that are formed — they go on the right side of the arrow.

• Know the symbols that indicate states of matter

These are written after each formula in an equation, like: NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)

• What is the law of conservation of mass?

Matter cannot be created or destroyed in a chemical reaction. The total mass of the reactants must equal the total mass of the products. This means every atom that goes in must come out — which is why we balance equations.

• What is the difference between a coefficient and a subscript? Which do you add to balance?

Coefficient = the big number in front of a formula. It multiplies the entire molecule. ✅ You change THIS to balance.

Subscript = the small number inside the formula. It tells how many of that atom are in one molecule. 🚫 NEVER change this — it changes the substance itself.

Example: In 2H₂O, the 2 is the coefficient (2 molecules) and the ₂ is the subscript (2 hydrogen per molecule). Total hydrogen = 2 × 2 = 4.

• List the rules for balancing equations

• Never change subscripts — only add or change coefficients
• Balance metals first, then non-metals, then oxygen, then hydrogen last
• Start with the most complex formula — anchor it with a coefficient of 1
• Use the odd-even trick — if an element is odd on one side and even on the other, double the odd side
• Keep polyatomic ions together — if SO₄, NO₃, PO₄, etc. appear intact on both sides, count them as one unit
• Always verify — recount every atom on both sides when done
• Reduce to lowest ratio — coefficients should be the smallest whole numbers possible

• Review rules for correctly writing chemical formulas

• The metal (cation) is always written first, the non-metal (anion) second: NaCl, not ClNa
• Use Roman numerals for transition metals to show charge: Iron(II) = Fe²⁺ → FeCl₂, Iron(III) = Fe³⁺ → FeCl₃
• Polyatomic ions with a subscript go in parentheses: Ca(OH)₂, not CaOH₂
• Use naming prefixes for covalent compounds: mono=1, di=2, tri=3, tetra=4, penta=5

• What is a diatomic element and what are the diatomic elements?

A diatomic element is one that naturally exists as a pair of two atoms bonded together when it's by itself (not in a compound).

"Have No Fear Of Ice Cold Beer" → H₂, N₂, F₂, O₂, I₂, Cl₂, Br₂

When these elements appear alone in an equation, always write them with a ₂ subscript.

• Which type of reaction would require you to use your activity series of metals?

Single Replacement — the activity series tells you whether the lone element is reactive enough to replace the element in the compound. Higher on the chart = more reactive = can replace. ↓ See the interactive Activity Series tool below.

• Which type of reaction would require the use of the solubility chart?

Double Replacement — after swapping the cations, the solubility chart tells you if a precipitate (insoluble solid) forms. If it does, the reaction happens. If all products are soluble, no reaction. ↓ See the interactive Solubility Chart below.

• Predict products — Solubility chart problems:

For these, swap the cations, then check the solubility chart. If all products are aqueous (soluble), write "No Reaction."