Chemical equation

A chemical equation i hate this class it suckz ass

Form

A chemical equation consists of the chemical formulas of the substances that are mixed (called the reactants), and the chemical formula of the substances that result from the chemical reaction (called the products). The two are separated by an → —usually read as "yields"— and each chemical formula is separated from others by a plus sign. Sometimes a triangle is drawn over the arrow symbol to denote energy must be added to the substances for the reaction to begin.

As an example, a reaction where hydrogen combines with oxygen to produce water can be denoted

H
₂+ O → H
₂O

This can be read as "H two plus O, yields H two O". Occasionally, rather than reading the letter and its subscript, the chemical formulas are read using compositional nomenclature (such as dihydrogen monoxide for H₂O). However, atomic oxygen is extremely rare in nature, oxygen is more frequently found in O₂ compounds. But making H₂ and O₂ react does not produce H₂O since that would be an unbalanced reaction (see "Balancing chemical equations" below).

For this reason, each chemical formula may be preceded by a scalar coefficient indicating the proportion of that substance necessary to produce the reaction in formula. For instance, the formula for the burning of methane

CH
₄+ 2 O
₂→ CO
₂+ 2H
₂O

indicates that twice as much O₂ as CH₄ is needed, and when they react will produce twice as much H₂O as CO₂. This is because during the reaction,each atom of carbon needs exactly two atoms of oxygen to combine with, to produce the CO₂, and every two atoms of hydrogen need an atom of oxygen to combine with to produce the H₂O. If the proportions of the reactants are not respected, when they are forced to react either not all of the substance used will participate in the reaction, or the reaction that will take place will be different from the one noted in the equation.

Balancing chemical equations

The law of conservation of mass dictates the quantity of each element does not change in a chemical reaction. Thus, each side of the chemical equation must represent the same quantity of any particular element. Similarly, the charge is conserved in a chemical reaction. Therefore, the same charge must be present on both sides of the balanced 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.

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 Nas 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 total and 2 O. Again, this is a problem, there must be an equal amount of each element on both sides. To fix this 2 more Na 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 on both sides of the equation. The left hand side has 4 P and the right hand side has 4 P. So the P atoms are balanced. The left hand side has 2 O and the right hand side has 10 O.

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

P₄ + 5O₂ → 2P₂O₅

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

Ionic equations

An ionic equation is a chemical equation in which electrolytes are written as dissociated ions. Ionic equations are used for single and double displacement reactions which occur in aqueous solutions. 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 ions and do not participate directly in the reaction, as they exist with the same oxidation state 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 or acid/base 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 with phosphoric acid because the insoluble salt barium phosphate is produced in addition to water.

Double displacement reactions that feature a carbonate reacting with an acid have the net ionic equation:

2 H⁺ + CO₃^2- → H₂O + CO₂

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

External links

• Chemical Equation Balancer - An open source chemical equation balancer.
• Classic Chembalancer - Play Chembalancer, a free online game at FunBasedLearning.com, to learn how to balance equations by inspection
• Online calculator, determines of the coefficients of a chemical equation
• Online Chemical Equation Balancer Balances equation of any chemical reaction (full or half-cell) in one click.
• Balance chemical equations Teaches how to balance chemical equations