Chapter 8

CHEMICAL REACTIONS

COMPONENTS OF A CHEMICAL REACTION

Reactants Catalyst Product(s) MnO2

Fe(s) + O2(g)Fe2O3(s)

State designations (s=solid, g=gas, l=-liquid, aq=aqueous)

 Arrow separates reactants from products

A skeleton equation is one that may not be balanced. If good formulas are written and the equation is balanced, you are done!

All formulas and states are written correctly. A catalyst is a substance that speeds up a

reaction but is not used in the reaction. 

BALANCING CHEMICAL EQUATIONS

In a balanced equation, the number and types of atoms on the reactant side must equal the number and types of atoms on the product side.

Rules for balancing

1. Determine correct formulas.2. Write reactant formulas left of arrow and

product formulas right of arrow.3. Count the number of atoms of each element

on each side of the equation (polyatomic ions can be counted as a single unit if they appear on both sides of the equation.)

4. Balance using coefficients. Coefficients may only be placed in front of a formula!

5. Check for conservation of mass6. Make sure coefficients are in the lowest

whole number ratio.

SYNTHESIS REACTIONS

Also called combination reactions General format: A + B C When a nonmetal oxide reacts with water, an acid is

produced. An acid is generally hydrogen bonded with a

nonmetal or polyatomic ion. SO2(g) + H2O(l) H2SO3 (aq) Nonmetal oxide + water acid

SYNTHESIS REACTIONS

When a metal oxide reacts with water, a base is produced.

A base consists of a metal and a(n) hydroxide ion.

CaO(s) + H2O(l) Ca(OH)2

Metal oxide water base 

DECOMPOSITION REACTIONS

General format: A B + C Difficult to predict products unless the

decomposing compound is binary. Usually requires energy to proceed.

DECOMPOSITION REACTIONS

Metal hydrogen carbonates are a special type of decomposition reaction.

A metal hydrogen carbonate undergoes decomposition when heated.

Format: metal hydrogen carbonate Metal carbonate + H2O + CO2

DECOMPOSITION REACTIONS

Metal carbonates can further decompose with prolonged heating.

General format: metal carbonate metal oxide +CO2

SINGLE REPLACEMENT REACTIONS

General format:A + BX B + AX (Metal switches)

or Y + AX X + AY (Halogen switches) Whether a RXN will proceed depends on the activity

of the metals or halogens involved. The activity series of metals and of halogens is used to

determine whether a RXN will proceed. A RXN will proceed if the elemental reactant is higher

in the series than the combined metal (or halogen)

DOUBLE REPLACEMENT REACTIONS

Involves the exchange of ions between two compounds.

General format: AX + BY AY + BXThese reactions usually take place when two ionic compounds are in aqueous solution

DOUBLE REPLACEMENT REACTIONS

For a double replacement reaction to occur one of the following is usually true: One product is only slightly soluble and precipitates

from solution. (a precipitate is a solid that is formed during a reaction of aqueous solutions)

One product is a gas that bubbles out of the mixture. One product is a molecular compound such as

water.

NEUTRALIZATION REACTIONS

An acid (HX) reacts with a base (BOH) to form an ionic compound and water.

General format: HX + BOH BX + HOH

Special type of double replacement reaction

COMBUSTION REACTIONS

A fuel reacts with oxygen to form water and carbon dioxide.

General format: fuel + O2 CO2 + H2O These are sometimes difficult to balance. Oxygen, carbon dioxide and water are always

located as described in the general format.

NET IONIC EQUATIONS

Once you have written and balanced a single or double replacement reaction, you may separate the ionic compounds into their constituent ions.

All aqueous solutions dissociate and must be separated

The resulting equation is called the complete ionic equation

NET IONIC EQUATIONS

Ions that appear exactly the same on each side of the equation are called spectator ions.

Spectator ions may be eliminated and the equation rewritten to obtain the net ionic equation.

NET IONIC EQUATIONS

Complete, balanced equation: AgNO3(aq) + NaCl(aq) AgCl(s) +

NaNO3(aq)

NET IONIC EQUATIONS

Dissociate all aqueous substances for complete ionic equation. Do not dissociate the solid!

Ag+(aq)+ NO3-(aq) + Na+(aq) + Cl-(aq)

AgCl(s) + Na+(aq) + NO3-(aq)

NET IONIC EQUATIONS

Cross out the spectator ions to get the net ionic equation

Ag+(aq)+ NO3-(aq) + Na+(aq) + Cl-(aq)

AgCl(s) + Na+(aq) + NO3-(aq)

 Ag+(aq) + Cl-(aq) AgCl(s)

Balancing the EASY way

1. Pick the largest compound2. Place a 1 in front. 3. Pick one of the elements (two places not three)4. Balance that element5. Repeat 3 4 56. If you are unable to balance one element, place a

2 in front of the starting compound and repeat.