A combustion reaction
Combustion reactions always involve molecular oxygen O2. Anytime anything burns (in the usual sense), it is a combustion reaction. Combustion reactions are almost always exothermic (i.e., they give off heat). For example when wood burns, it must do so in
oxidation-reduction reactions
electrons are transferred from one substance to another.
chemical reaction
transformation of a substance into a different substance
precipitation reaction
occur when cations and anions in aqueous solution combine to form an insoluble ionic solid called a precipitate. Whether or not such a reaction occurs can be determined by using the solubility rules for common ionic solids. Reactions such as these�that fo
evidence of a chemical reaction:
A color change
� The formation of a solid in a previously clear (unclouded) solution
� The formation of a gas when you add a substance to a solution
� The emission of light
� The emission or absorption of heat
Boiling water forms gaseous steam, but both water and steam are composed of water molecules, therefore:
no chemical change has occurred
The changes occurring at the atomic and molecular level determine whether a chemical reaction has taken place.
Only chemical analysis that shows that the initial substances have changed into other substances conclusively proves that a chemical reaction has occurred.
Chemical reactions may occur without any obvious signs, yet chemical analysis may show that a react
(aq)
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be represented
(g)
gas
(l)
liquid
(s)
solid
reactants
starting compounds/elements
products
ending compounds/elements
solving tips
If an element occurs in only one compound on both sides of the equation, balance it first. If there is more than one such element, balance metals before nonmetals.
If an element occurs as a free element on either side of the chemical equation, balance it
A compound is soluble in a particular liquid if :
it dissolves in that liquid
A compound is insoluble if :
it does not dissolve in the liquid.
An aqueous solution is a
homogeneous mixture of a substance with water.
When ionic compounds dissolve in water, they usually dissociate into :
their component ions.
strong electrolytes:
Substances (such as NaCl) that completely dissociate into ions in a solution.
strong electrolyte solutions.
Solutions such as NaCl(aq)
Pure water does not conduct electricity.
(b) Ions in a sodium chloride solution conduct electricity, causing the bulb to light.
When compounds containing polyatomic ions such as NO3? dissolve: the polyatomic ions dissolve as intact units
the polyatomic ions dissolve as intact units
Not all ionic compounds dissolve in water.
AgCl does not dissolve in water.
A compound is soluble in a particular liquid if:
it dissolves in that liquid
; a compound is insoluble if
it does not dissolve in the liquid
Precipitation Reactants
Reaction in aqueous solution that forms a solid.
Sodium carbonate in laundry detergent reacts with dissolved Mg2+ and Ca2+ ions to form solids that precipitate from solution.
These reactions are examples of precipitation reactions, reactions that form a s
The key to predicting precipitation reactions is understanding that only :
insoluble compounds form precipitates.
In a precipitation reaction, two solutions containing soluble compounds combine and an insoluble compound precipitates.
spectator ions
In the complete ionic equation, some of the ions in solution appear unchanged on both sides of the equation.
molecular equation
is an equation showing the complete neutral formulas for every compound in the reaction.
Complete ionic equations
show aqueous ionic compounds that normally dissociate in solution as they are actually present in solution.
net ionic equations
To simplify the equation, and to more clearly show what is happening, spectator ions can be omitted.
Equations such as this one, which show only the species that actually participate in the reaction, are called
To summarize:
A molecular equation is a chemical equation showing the complete, neutral formulas for every compound in a reaction.
A complete ionic equation is a chemical equation showing all of the species as they are actually present in solution.
A net ionic equation
Acid-base reactions
are reactions that form water upon mixing of an acid and a base.
Reactions involving the transfer of electrons are called :
oxidation-reduction reactions or redox reactions
rusting of iron, the bleaching of hair, and the production of electricity in batteries.
Many redox reactions involve the reaction of a substance with oxygen.
oxidation
is the loss of electrons.
reduction
the gain of electrons
OIL RIG
Oxidation Is Loss; Reduction Is Gain.
LEO GER
Lose Electrons Oxidation; Gain Electrons Reduction
Redox reactions are those in which the following occurs:
A substance reacts with elemental oxygen.
A metal reacts with a nonmetal.
More generally, one substance transfers electrons to another substance.
Combustion reactions
type of redox reaction.
Combustion reactions are characterized by the reaction of a substance with O2 to form one or more oxygen-containing compounds, often including water.
Combustion reactions are exothermic (they emit heat).
Compounds containing carbon
Synthesis Reactions
A+B= AB
In a synthesis reaction, two simpler substances combine to make a more complex substance. In this series of photographs we see sodium metal and chlorine gas. When they combine, a chemical reaction occurs that forms sodium chloride.
Decomposition Reaction
AB = A+B
a complex substance decomposes to form simpler substances.
When electrical current is passed through water, the water undergoes a decomposition reaction to form hydrogen gas and oxygen gas.
Single Displacement Reaction
A+BC = AC+B
one element displaces another in a compound.
When metallic zinc is immersed in a solution of copper(II) chloride, the zinc atoms displace the copper ions in solution.
Double displacement Reaction
AB+CD = AD+CB
two elements or groups of elements in two different compounds exchange places to form two new compounds.
A double-displacement reaction follows the general form
AB + CD ? AD + BC
The kinds of reactions that may be double displacements are pr
Chemical reactions:
One or more substances�either elements or compounds�change into a different substance.
Evidence of a chemical reaction:
The only absolute evidence for a chemical reaction is chemical analysis showing that one or more substances have changed into another substance.
However, one or more of the following often accompanies a chemical reaction: a color change; the formation of
Chemical equations:
Chemical equations must be balanced to reflect the conservation of matter in nature.
Aqueous solutions and solubility:
If a substance dissolves in water, it is soluble.
Some specific types of reactions:
precipitation reaction, acid-base reaction, gas evolution reaction, redox reaction, and combustion reaction.
Chemical reaction classifications are:
synthesis reaction, decomposition reaction, single-displacement reaction, and double-displacement reaction.