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What are chemical equations and how are they balanced?

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enotes | Valedictorian

Posted March 3, 2014 at 11:17 PM via web

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What are chemical equations and how are they balanced?

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Payal Khullar | College Teacher | (Level 2) Associate Educator

Posted March 4, 2014 at 5:04 PM (Answer #1)

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A chemical reaction happens when one chemical substance changes into another one. This chemical transformation might occur along with physical changes like release of heat or light, change in colour, etc. Chemical reactions obey the rules of nature. A chemical equation is nothing but a rule-based, mathematical or symbolic representation of a chemical reaction.

A chemical equation has two sides- left hand side and right side. The chemical elements at the left hand side (L.H.S) are called reactants and those at the right hand side (R.H.S) are called products. In simple terms, the reactants react to form the products. In order to balance a chemical equation, one has to take the following steps:

  • Identify the reactants and products of the chemical reaction and represent them using their chemical symbols or formulae.
  • Count the number of atoms of an element on the L.H.S. and R.H.S. The number of atoms of an element on the L.H.S should always be equal to that on the R.H.S. For doing this, one has to adjust the stoichiometric coefficient of the species that contains the element to be balanced. This is to be done for all the atoms of the chemical reaction.

We will take an example of an unbalanced chemical equation and balance it. 

H2 + O2 `->` H2O

In the above chemical reaction, Hydrogen and Oxygen react to form water. Now, there are two atoms of Hydrogen and two atoms of Oxygen on the L.H.S. But on the R.H.S, there are two atoms of Hydrogen and only one atom of Oxygen.

Note that we cannot disturb the number of Oxygen atoms in the Oxygen molecule (if we make O2 as O, it will no longer be Oxygen). We can only adjust the stoichiometric coefficients.

To balance it, thus, we can do the following:

H2 + O2 `->` 2H2O

Now, Oxygen is balanced as both L.H.S and R.H.S have two Oxygen atoms. Doing this step, however, made 4 atoms of Hydrogen on the R.H.S.

2H2 + O2 `->` 2H2O

Now the chemical equation is balanced!

Sources:

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ayl0124 | Student, Grade 12 | Valedictorian

Posted May 15, 2014 at 7:38 PM (Answer #2)

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A chemical equation displays a chemical reaction, using the molecular formulas. Some components of a chemical equation is the states of matter, catalysts, and the ratio of chemicals. Some reactions also have double arrows, which means the reaction is reversible. 

An important concept you must remember about balancing chemical equations is that matter cannot be created nor destroyed.

Take a simple chemical equation from a precipitate reaction.

2 NaOH (aq) + MgCl2 (aq) -> 2 NaCl (aq) + Mg(OH)2 (s)

The first thing you must do when balancing equations is making sure all the charges match up. Mg2+ has a 2+ charge and needs two Cl- ions. Similarly, it needs two OH- ions because of its 1- charge.

Count how many ions of each element there are. 

In the unbalanced equation:

NaOH + MgCl2 -> NaCl + Mg(OH)2

There are (in the reactants):

  • 1 Na+
  • 1 OH- (keep polyatomic ions as one single unit)
  • 1 Mg2+
  • 2 Cl-

There are (in the products):

  • 1 Na+
  • 2 OH-
  • 1 Mg2+
  • 1 Cl-

You can see some numbers do not match up. Add coefficients accordingly to make sure that the number of ions on each side of the reaction are equal. I suggest balancing metals first and elements such as H or O last. 

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