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Chemical equation
 
 
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A chemical equation may be described as a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 or a means of writing out and describing such a phenomenon. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin
Jean Beguin

Jean Beguin was an iatrochemist noted for his 1610 Tyrocinium Chymicum , which many consider to be one of the first chemistry textbooks. In the 1615 edition of his textbook, Beguin made the first-ever chemical equation or rudimentary reaction diagrams, showing the results of reactions in which there are two or more reagents....
 in 1615.

law of conservation of mass
Conservation of mass

The law of conservation of mass/matter, also known as law of mass/matter conservation says that the mass of a closed system will remain constant, regardless of the processes acting inside the system....
 dictates the quantity of each element does not change in a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
.






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Encyclopedia


A chemical equation may be described as a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 or a means of writing out and describing such a phenomenon. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin
Jean Beguin

Jean Beguin was an iatrochemist noted for his 1610 Tyrocinium Chymicum , which many consider to be one of the first chemistry textbooks. In the 1615 edition of his textbook, Beguin made the first-ever chemical equation or rudimentary reaction diagrams, showing the results of reactions in which there are two or more reagents....
 in 1615.

Balancing chemical equations

The law of conservation of mass
Conservation of mass

The law of conservation of mass/matter, also known as law of mass/matter conservation says that the mass of a closed system will remain constant, regardless of the processes acting inside the system....
 dictates the quantity of each element does not change in a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
. Thus, each side of the chemical equation must represent the same quantity of any particular element. Similarly, the charge is conserved
Charge conservation

Charge conservation is the principle that electric charge can neither be created nor destroyed. The quantity of electric charge is always conserved....
 in a chemical reaction. Therefore, the same charge must be present on both sides of the unbalanced equation.

One balances a chemical equation by changing the scalar number for each molecular formula. Simple chemical equations can be balanced by inspection, that is, by trial and error. Another technique involves solving a system of linear equations
System of linear equations

In mathematics, a system of linear equations is a collection of linear equations involving the same set of variables. For example,is a system of three equations in the three variables ....
.

Example #1: Na + O2 ? Na2O

In order for this equation to be balanced, there must be an equal amount of Na on the left hand side as on the right hand side. As it stands now, there is 1 Na on the left but 2 Na's on the right. This is solved by putting a 2 in front of the Na on the left hand side:

2Na + O2 ? Na2O


In this there are 2 Na atoms on the left and 2 Na atoms on the right. In the next step the oxygen atoms are balanced as well. On the left hand side there are 2 O atoms and the right hand side only has one. This is still an unbalanced equation. To fix this a 2 is added in front of the Na2O on the right hand side. Now the equation reads:

2Na + O2 ? 2Na2O


Notice that the 2 on the right hand side is "distributed" to both the Na2 and the O. Currently the left hand side of the equation has 2 Na atoms and 2 O atoms. The right hand side has 4 Na's total and 2 O's. Again, this is a problem, there must be an equal amount of each chemical on both sides. To fix this 2 more Na's are added on the left side. The equation will now look like this:

4Na + O2 ? 2Na2O


This equation is a balanced equation because there is an equal number of atoms of each element on the left and right hand sides of the equation.

Example #2:
P4 + O2 ? 2P2O5


This equation is not balanced because there is an unequal amount of O's on both sides of the equation. The left hand side has 4 P's and the right hand side has 4 P's. So the P atoms are balanced. The left hand side has 2 O's and the right hand side has 10 O's.

To fix this unbalanced equation a 5 in front of the O2 on the left hand side is added to make 10 O's on both sides resulting in

P4 + 5O2 ? 2P2O5


The equation is now balanced because there is an equal amount of substances on the left and the right hand side of the equation.

Ionic equations


An ionic equation is a chemical equation in which electrolyte
Electrolyte

An electrolyte is any substance containing free ions that behaves as an electrical conductor medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutions, but molten electrolytes and solid electrolytes are also possible....
s are written as dissociated ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s. Ionic equations are used for single
Single displacement reaction

A single-displacement reaction, also called single-replacement reaction, is when an element or ion moves out of one compound and into another....
 and double displacement reactions which occur in aqueous solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s. For example in the following precipitation reaction: CaCl2(aq) + 2AgNO3(aq) → Ca(NO3)2(aq) + 2AgCl(s)

the full ionic equation would be: Ca2+ + 2Cl- + 2Ag+ + 2NO3- → Ca2+ + 2NO3- + 2AgCl(s)

and the net ionic equation would be: 2Cl-(aq) + 2Ag+(aq) → 2AgCl(s)

or, in reduced balanced form, Ag+ + Cl- → AgCl(s)

In this aqueous reaction the Ca2+ and the NO3- ions remain in solution and are not part of the reaction. They are termed spectator ion
Spectator ion

A spectator ion is an ion that exists as a reactant and a product in a chemical equation. Spectator ions can be observed in the reaction of aqueous solutions of sodium chloride and copper sulfate:...
s and do not participate directly in the reaction, as they exist with the same oxidation state
Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
 on both the reactant and product side of the chemical equation. They are only needed for charge balance of the original reagents.

In a neutralization
Neutralization

In chemistry, neutralization is a chemical reaction in which an acid and a base or alkali react to produce salt and water.During the process, hydrogen ions H+ from the acid or a hydronium H3O+ and hydroxide ions OH- or oxide ions O2- from the base react together to form a water mo...
 or acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
/base
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
 reaction, the net ionic equation will usually be:

H+ + OH- → H2O

There are a few acid/base reactions that produce a precipitate in addition to the water molecule shown above. An example would be the reaction of barium hydroxide
Barium hydroxide

Barium hydroxide is the chemical compound with the chemical formula Ba2. Also known as baryta, it is one of the principal compounds of barium....
 with phosphoric acid
Phosphoric acid

Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula Hydrogen3PhosphorusOxygen4....
 because the insoluble salt barium phosphate is produced in addition to water.

Double displacement reactions that feature a carbonate
Carbonate

In chemistry, a carbonate is a salt or ester of carbonic acid....
 reacting with an acid have the net ionic equation:

2 H+ + CO32- → H2O + CO2

NaCl(aq)+AgNO3(aq)?AgCl(s)+NaNO3(aq).

If every ion is a "spectator ion", then there was no reaction, and the net ionic equation is null.

See also

  • Solubility
    Solubility

    Solubility is often seen as a property of a substance; for instance the solubility of a solid substance usually refers to the concentration of the substance in a liquid that has reached equilibrium with the substance in solid phase ....
  • Chemistry
    Chemistry

    Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....


External links

  • - Play Chembalancer, a free online game at FunBasedLearning.com, to learn how to balance equations by inspection
  • , determines of the coefficients of a chemical equation
  • Balances equation of any chemical reaction (full or half-cell) in one click.
  • Teaches how to balance chemical equations