"The price of greatness is responsibility." Sir Winston Churchill

From Wikipedia, the free encyclopedia.

This article needs to be cleaned up to conform to a higher standard of quality. This article has been tagged since July 2005. See Help:Editing and Category:Wikipedia help for help, or this article's talk page.

A chemical equation is a mathematical method used to display the ‘before’, the ‘transition’, and ‘after’ stages for chemical reactions, wherein substances are changed into other substances. The species to the left of the arrow represent the reactants, the arrow represents the transition stage, and the species to the right of the arrow represent the products. The four basic chemical equations are:

A → B

A → B + C

A + B → C

A + B → B + C

For example, the combustion of methane in oxygen is:

CH₄ + 2 O₂ → CO₂ + 2 H₂O,

and the reversible reaction of the Haber process is

N_2(g) + 3H_2(g) ↔ 2NH_3(g) + ΔH.

Contents [hide] 1 Reading Chemical Equations 2 Balancing Chemical Equations 3 See also 4 External links

 

Reading Chemical Equations

• Each side of an equation represents a mixture of chemicals. The mixture is written as a set of molecular formulas, separated by + symbols.
• Each formula is preceeded by an optional scaler number (if no scaler number is written, it is implied that the number is 1). The scaler numbers indicate the relative quantity of molecules in the reaction. For instance, the string 2H₂O + 3CH₄ represents a mixture containing 2 molecules of H₂O for every 3 molecules of CH₄.
• The two sides of the equation are separated by an arrow. If the reaction is non-reversable, a right-arrow (→) is used, indicating that the left side represents the mixture of chemicals before the reaction, and the right side indicates the mixture after the reaction. For a reversible reaction, a two-way arrow is used.

Example: 4Na + O₂ → 2Na₂O

This equation represents a non-reversible reaction. In this reaction, sodium(Na) and oxygen(O₂) are converted to a single molecule, Na₂O (containing 2 sodium atoms and 1 oxygen atom). We can also see that for every 4 sodium atoms at the beginning of the reaction, a single O₂ molecule will participate, and 2 Na₂O molecules will result.

 

Balancing Chemical Equations

In a chemical reaction, the quantity of each element does not change. Thus, each side of the equation must represent the same quantity of any particular element. Also in case of net ionic reactions the same charge must be present on both sides of the equation. Then, and only then, the equation is balanced. Given an unbalanced equation, one may balance it by changing the scaler number for each molecular formula.

Simple chemical equations can be balanced by inspection, that is, by trial and error. Generally, it is best to balance the most complicated molecule first.

Let's look at a few examples and walk through it:

Ex #1. Na + O₂ → Na₂O

In order for this equation to be balanced, there must be 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. We solve this problem by putting a 2 in front of the Na on the left hand side, Like this:

    2Na + O2 → Na2O

So now we see, there are 2 Na's on the left and 2 Na's on the right. But what about the O's? We now must check to see if the O's are balanced on both sides of the equation. On the left hand side there are 2 O's and the Right hand side only has one. This is still an unbalanced equation. To fix this we must put a 2 in front of the Na₂O on the right hand side. Now our 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's and 2O's. 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 let's add 2 more Na's on the left side. The equation will now look like this:

    4Na + O2 → 2Na2O

So now, as you can see, we have a balanced equation because there is an equal amount of element's on the left and right hand sides of the equation.

Ex #2. P₄ + O₂ → P₄O₁₀

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's balance. Let's look at the O's. The left hand side has 2 O's and the right hand side has 10 O's. To fix this unbalanced equation we must put a 5 in front of the O₂ on the left hand side to make 10 O's on both sides. Let's take a look at what this looks like:

        P4 + 5O2 → P4O10

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

Ex #3. C₂H₅OH + O₂ → CO₂ + H₂O

This equation is more complex than the previous examples; it will take a few steps. The most complicated molecule here is C₂H₅OH, so we begin by placing the coefficient 2 before the CO₂ to balance the carbon atoms.

        C2H5OH + O2 →  2CO2 + H2O

Since C₂H₅OH contains 6 hydrogen atoms, the hydrogen atoms can be balanced by placing 3 before the H₂O, like this:

        C2H5OH + O2 →  2CO2 + 3H2O

Finally we balance the oxygen atoms. Since there are 7 oxygen atoms on the right and only 3 on the left, we balance it by placing a 3 before O₂, to produce the balanced equation:

        C2H5OH + 3O2 →  2CO2 + 3H2O