Types of Chemical Reactions

There are five main types of chemical reactions that we will be covering in this chapter:– Combination reactions– Decomposition reactions– Single-Replacement reactions– Double-Replacement reactions– Combustion reactions

Combination Reactions

In a combination reaction, two or more substances combine to form a single substance.

General Equation:

R + S RS

Example:

Mg(s) + O2 (g) MgO(s)

Decomposition Reactions

In a decomposition reaction a single compound is broken down into two or more products.

General Equation:

RS R + S

Example:

HgO(s) Hg(l) + O2

Single-Replacement Reactions

In a single-replacement reaction, one element replaces a second element in a compound.

General Equation:

T + RS TS + R

Example:

K(s) + H2O(l) KOH(aq) + H2 (g)

Double-Replacement ReactionsDouble-replacement reactions involve an exchange of positive ions (or cations) between two reacting compounds. These reactions generally produce a precipitate, a gaseous product, or water.

General Equation:

R+S- + T+U- T+S- + R+U-

Example:

K2CO3 (aq) + BaCl2 (aq) BaCO3 (s) + KCl(aq)

Combustion Reactions

In a combustion reaction an element or a compound (often a hydrocarbon) reacts with oxygen, often producing energy as heat and light. The products of these types of reactions are carbon dioxide and water.Example: The combustion of methane gas in air

__CH4 (g) + __O2 (g) __CO2 (g) + __H2O(g)

Combustion Reactions

The reaction between some elements and oxygen is also an example of a combustion reaction. For example:

__Mg(s) + __O2 (g) __MgO(s)

Here Mg acts as the fuel for the reaction and when reacted with O2 (g) will for an oxide – in this case magnesium oxide (MgO(s)). What other type of chemical reaction does this look like?

Combination Reactions

Complete and balance the following combination reactions:

Be + O2

H2 + O2 H2O

Decomposition Reactions

Complete and balance the following decomposition reactions:

HI

Mg(ClO3)2 MgCl2 +

Single-Replacement Reactions and Activity Series

For example:

Mg(s) + Zn(NO3)2 (aq)

Mg(s) + AgNO3 (aq)

Mg(s) + LiNO3 (aq)

Single-Replacement Reactions

Complete the equations for the following single replacement reactions that take place in aqueous solution. Balance each equation. If a reaction does not occur (use activity series) write “no reaction.”

Fe(s) + Pb(NO3)2 (aq)

Cl2 (g) + NaI(aq)

Ca(s) + H2O(l)

Double-Replacement Reactions and the Solubility Rules

Mixing the solutions of two ionic compounds can sometimes result in the formation of an insoluble salt called a precipitate.

In order for a double-replacement reaction to occur there must be fewer ions in solution when the two compounds are mixed. Otherwise all we have is a mixture.

Recall our conductivity demo – when ionic compounds dissociate they can conduct electricity.

Double-Replacement Reactions

We also have fewer ions in solution if we produce a gas or water.

Double-Replacement Reactions

Write the products for the following reactions. Then balance each equation.

NaOH(aq) + Fe(NO3)3 (aq)

Ba(NO3)2 (aq) + H3PO4 (aq)

Double-Replacement Reactions and the Solubility Rules

Should a precipitate form when aqueous solutions of Na2SO4 (aq) and Ba(NO3)2 (aq) are mixed?

Double-Replacement Reactions and the Solubility Rules

Should a precipitate form when aqueous solutions of NaCl(aq) and Zn(NO3)2 (aq) are mixed?

Combustion Reactions

Predict the product of the following combustion reaction:

S(s) + O2 (g)

Combustion ReactionsWrite a balanced equation for the complete combustion of each compound.– Heptane (C7H16)

– Glucose (C6H12O6)

Rates of Reaction

There are three main factors that effect the rates of chemical reactions:– The presence of a catalyst– Temperature– Concentration

Catalysts

The presence of a catalyst in a chemical reaction will speed up the reaction while not being used up in the reaction itself. Because a catalyst is neither a reactant nor a product, its formula is written above the yields sign () in a chemical equation.

Catalysts

For a reaction to occur between two substances (or reactants) particles of those substances must collide. Not only that, they must hit each other with enough force to cause a change to take place. The amount of energy the particles must have when they collide is called the Activation Energy.

Catalysts are used to lower activation energy.

Temperature

Most reactions go faster at high temperatures.– Ex: Baking a cake speeds up the reactions

that change the liquid batter into a spongy product.

Lowering the temperature slows down most reactions.– Batteries tend to last longer if they are kept

cool, slowing down the reaction that takes place within them.

Concentration

Concentration – The amount of substance present in a certain volume.

Raising the concentration of a reactant will speed up a reaction because there are more particles per volume.

More particles = more collisions = increase in reaction rate.