OB: All about decomposition reactions

Decomposition reactions are the opposite of synthesis, where a larger reactant is broken down into 2 or more smaller products

AB A + B or XYZ X + YZ

In a decomposition reaction there is always ONE REACTANT, and 2 or more products

Examples….

Lead II oxide decomposes into lead and oxygen

2PbO 2Pb + O2 (balanced)

Demo Diagram #2 Decomposition Reaction (new sheet of paper, name on top too)

Decomposition reactions require one reactant to break down into 2 or more smaller products

Abstract: ABC AB + C

Word equationhydrogen peroxide decomposes into water & oxygen gas

Skeleton equation H2O2 H2O + O2

Balanced Chemical Reaction

2H2O2(L) 2H2O(L) + O2(G)

[back and forth, back and forth, pull your hair if you need to. Count the atoms on the reactant side and compare to the product side.

Four hydrogen in reactant, four in product, four oxygen in reactant, 2 + 2 = 4 in product]

This reaction is SO SLOW, that watching it is for the birds (you can put that in your notes).

You can’t hurry love, you just have to wait… but in chemistry you can hurry things up.

You need to add a CATALYST

2H2O2(L) 2H2O(L) + O2(G)

By adding the potassium iodide catalyst, things go much faster. Write that catalyst above the arrow in the reaction. That shows it’s been added, but it does not affect the reaction except for how fast it goes. (real fast!). The exact same reaction occurs with a catalyst as without, but when things happen fast, they appear to be different. NO DIFFERENCE in products, or amount of energy released, just FASTER.

KI

Draw a picture

H2O2

becomes water

No catalyst, slow, decomposition happens, energy is released slowly

Add some KI catalyst

Excitement pops out the top, because the reaction is LOTS faster than before.

This is the end of the demo diagram #2

Use the following decomposition reaction word equations to create skeleton equations which you will balance properly with PHASE SYMBOLS.

Magnesium nitride decomposes into magnesium & nitrogen.

Use the following decomposition reaction word equations to create skeleton equations which you will balance properly with PHASE SYMBOLS.

Magnesium nitride decomposes into magnesium & nitrogen.

Mg3N2(S) 3Mg(S) + N2(G)

Magnesium carbonate decomposes into carbon dioxide & magnesium oxide

Magnesium carbonate decomposes into carbon dioxide & magnesium oxide

MgCO3(S) CO2(G) + MgO(S)

Iron (II) oxide decomposes

Iron (II) oxide decomposes

2FeO(S) O2(G) + 2Fe(S)

AMMONIA gas decomposes

Hydrogen monochloride gas decomposes to hydrogen & chlorine gases

Tonight: Reactions HW #1 to be collected Wed.

AMMONIA decomposes

NH3(G) N2(G) + H2(G)

2NH3(G) N2(G) + 3H2(G)

Hydrogen monochloride gas decomposes to hydrogen & chlorine gases

HCl(G) H2(G) + Cl2(G)

2HCl(G) H2(G) + Cl2(G)

Tonight: Reactions HW #1 to be collected Wed.