4.2 Synthesis and Decomposition Reactions

Synthesis Reactions Involves smaller atoms or molecules combining to form a larger molecule Two or more reactants combine to make one product element + element → compound Synthesis reactions of non-metals create molecular compounds Synthesis reactions can involve compounds coming together compound + compound → new compound

General Equation

Synthesis Reactions involving Hydrogen Usually forms a molecular compound H2(g) + Cl2 (g) → HCl(g) H2(g) + Cl2 (g) → 2HCl(g)

Example Ex. 1) Hydrogen + oxygen → water H2(g) + O2(g) → H2O (l) 2H2(g) + O2(g) → 2H2O (l) balanced!

Synthesis Reactions Involving Other Reactions Can be more difficult to predict C(s) + O2 (g) → CO2(g) OR 2 C(s) + O2(g) → 2 CO(g) In these cases, the only way to identify the reaction products is by conducting chemical tests.

Examples Sodium + chlorine → sodium chloride Na (s) + Cl2(g) → NaCl (s) 2Na(s) + Cl2(g) → 2NaCl(s) 3 )Copper + Oxygen → copper (ll) oxide Cu(s) + O2(g) → CuO(s) 2Cu(s) + O2(g) → 2CuO(s)

Synthesis Involving Compounds This is an important reaction that impacts aquatic ecosystems. Carbonic Acid: raises the pH of our oceans. Eats at the shells of shelled animals and causes other problems for ocean life. CO2 (aq) + H2O → H2CO3 (aq)

Decomposition Reaction Opposite to synthesis Involves a large molecule splitting to form smaller molecules or elements One reactant breaks apart into two or more products The general equation for a decomposition reaction is: compound → element + element

Examples! 1) Water → Hydrogen + Oxygen H2O (l) → H2 (g) + O2 (g) 2) Triiodine mononitride→ Nitrogen + Iodine l3N (s) → N2(g) + l2 (l) 2l3N (s) → N2(g) + 3l2 (l) balanced!