Do I need a magic 8 ball for this?

• When predicting products of chemical equations, you will only be given the reactant side of the equation.

– Reactants Products

• In order to determine the products, you must recognize the reaction type.

There are five reaction types that we will consider.

1. Synthesis

2. Decomposition

3. Single Replacement

4. Double Replacement

5. Combustion

If it is a Synthesis reaction. . .

• Synthesis follows the general equation– A + B AB– This means that the reactants come together.

• In Synthesis reactions, there will be only one product.

• There will be more than one reactant.

If it is a Synthesis reaction. . .

• These reactants can be either elements or compounds.

• If there are only two elements, than the reaction is Synthesis.

If it is a Decomposition reaction. . .

• Decomposition reactions have the general equation of– AB A + B– This means that the reactant will be broken

down into simpler substances.

• In a Decomposition reaction, there will only be one reactant.

If it is a Single Replacement reaction. . .

• Single Replacement reactions follow the general equation of– AB + C AC + B– This means that the single element may

replace part of the compound.

• Reactants will have one compound and one element.

If it is a Double Replacementreaction . . .

• Double Replacement reactions follow the general equation of– AX + BY AY + BX– In these reactions, the reactants switch parts

to create two new products.

• There must be two compounds on the reactants side.

If it is a Combustion reaction. . .

• Combustion reactions do not have a specific general equation.

• These may overlap with Synthesis reactions, but they do have different products.

• Combustion reactions will always have O2 on the reactants side.

• Knowing the reaction type will allow us to realize what we must do.

• Each reaction type will have a different process to reach the correct product.

Synthesis Products

• H2 + N2 – There are two elements. This is a Synthesis

reaction.– Draw the Lewis structure for each element.

Synthesis Products

– The Lewis Dot Structure shows how many bonds each atom can make.

– How many bonds can hydrogen make?• One single bond

Synthesis Products

– How many bonds can nitrogen make?• One triple bond• One double bond and one single bond• Three single bonds

Synthesis Products

– Looking at both elements, choose the bonds that suit the situation.

– For our hydrogen and nitrogen, single bonds are the answer.

Synthesis Products

• Looking at the Lewis dot structures, determine the ratio of elements.

Synthesis Products

• Our product will have the formula of NH3.

Synthesis Products

• H2 + N2 NH3

• This is our equation with our predicted products.

• Is it the final equation?– No

• What is wrong?– It’s not balanced.

Synthesis Products

• Final step is to balance the equation.

• 3H2 + N2 2NH3

Decomposition Products

• Ba(OH)2

• There is only one reactant, so it is a Decomposition reaction.

• There must be at least two products.

• Look at the reactant.

• What two compounds could have made it?

Decomposition Products

• Ba(OH)2

• When there is a hydroxide group (the OH), then there will be water as one of the products.

• Next, we must look at the element attached to the hydroxide group. – Elements combining with water tend to be in

oxide form.

Decomposition Products

• Ba(OH)2 H2O + BaO

• The last step is always to balance equations.

• This equation is always balanced.

Decomposition

• Some nonmetal oxides, such as the halogen oxides, also decompose upon heating– Cl2O5

Decomposition

• Other nonmetal oxides, such as dinitrogen pentoxide, decompose to an element and a compound:– 2N2O5 (g) → O2 (g) + 4NO2 (g)

Decomposition

• Many metal salts containing oxoanions decompose upon heating. These salts either give off oxygen gas, forming a metal salt with a different nonmetal anion, or they give off a nonmetal oxide, forming a metal oxide. For example, metal nitrates containing Group 1A or 2A metals or aluminum decompose to metal nitrites and oxygen gas:

• Mg(NO3)2 (s) → Mg(NO2)2 (s) + O2 (g)

Decomposition

• All other metal nitrates decompose to metal oxides, along with nitrogen dioxide and oxygen:

• 2Cu(NO3)2 (s) → 2CuO (s) + 4NO2 (g) + O2 (g)

Decomposition

• Salts of the halogen oxoanions decompose to halides and oxygen upon heating:

• 2KBrO3 (s) → 2KBr (s) + 3O2 (g)

Decomposition

• Carbonates, except for those of the alkali metals, decompose to oxides and carbon dioxide.

• CaCO3 (s) → CaO (s) + CO2 (g)

Decomposition

• A number of compounds—hydrates, hydroxides, and oxoacids—that contain water or its components lose water when heated. Hydrates, compounds that contain water molecules, lose water to form anhydrous compounds, free of molecular water.

• CaSO4 · 2H2O (s) → CaSO4 (s) + 2H2O (g)

Decomposition

• Metal hydroxides are converted to metal oxides by heating:

• 2Fe(OH)3 (s) → Fe2O3 (s) + 3H2O (g)

Decomposition

• Most oxoacids lose water until no hydrogen remains, leaving a nonmetal oxide:

• H2SO4 (l) → H2O (g) + SO3 (g)

Decomposition

• Oxoanion salts that contain hydrogen ions break down into the corresponding oxoanion salts and oxoacids:

• Ca(HSO4)2 (s) → CaSO4 (s) + H2SO4 (l)

Single Replacement Product

• Single Replacement reactions do not always occur.

• For these reactions, we must look at an activity series.– An activity series shows the reactivity of

elements.– If the single element in the reaction is less

reactive than the element in the compound, the reaction will not occur.

Single Replacement Product

• Open your textbooks to page 293

• Now let’s look at– Al + HCl

• Look at the reactivity series. In this case, the aluminum is attempting to replace the hydrogen.

Single Replacement Product

• The Aluminum will replace the hydrogen.

• So what happens?

Single Replacement Product

• We know our two products will be hydrogen by itself and aluminum bonded with chlorine.

• Looking at hydrogen first, what do we know about hydrogen?– It’s diatomic.

– It will be written as H2.

Single Replacement Product

• Now we look at our aluminum and chlorine.

• Once again draw Lewis structures.

• AlCl3• Our final equation

– Al + HCl H2 + AlCl3

• Last thing to do is balance.

Single Replacement Product

• 2Al + 6HCl 3H2 + 2AlCl3

Double ReplacementProduct

• Ca(OH)2 + HCl

• In this reaction, there will be two compounds on the reactants side.

• There will also be two compounds on the product’s side.

Double ReplacementProduct

• These reactions produce water, a precipitate or a gas.

• Ca(OH)2 + HCl

• In this reaction, there is a hydroxide group, and a hydrogen.

• Water will be one of the products: H2O

Double ReplacementProduct

• The other product will result from the remaining elements.– Ca– Cl

• Calcium has two valence electrons.

• Chlorine has seven.

• From an ionic standpoint, the calcium needs two chlorines to form an ionic bond.

Double ReplacementProduct

• CaCl2 is the other product.

• Once again, the last step is to balance the equation.

• Ca(OH)2 + 2HCl 2H2O + CaCl2

Combustion Products

• Often composed of hydrocarbons– C(n)H(m)

• Reacting with O2

• CH4 + O2

• In cases of hydrocarbons, there will be two products– CO2 and H2O

Combustion Products

• The last step is to balance.

• CH4 + 2O2 2H2O + CO2

The End