Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. It is the study of the relationship between the number of mole of the reactants and product of a chemical reaction. Stoichiometric equation is a short scientific representation of a chemical reaction. The quantities are expressed as grams or moles.

Rules For Writing Stoichiometric Equations:

It takes practice to be able to write balanced equations. Three step process.

Rules For Writing Stoichiometric Equations:

It takes practice to be able to write balanced equations. Three step process.

- Write the unbalanced equation.
- Balance the equation.
- Indicate the state of matter of the reactant and product.

- Chemical formulas of reactants are listed on the left hand side of the arrow with a positive sign between them.
- Chemical formula of the products are listed on the right hand side of the equations.More than one product , a positive sign is placed between them.
- Reactants and products are separated by putting an arrow between them to show the directions of the reaction.
- The equation thus obtained above all three steps is called Skeleton equation. For example the chemical reaction between iron and oxygen producing Fe
_{2}O_{3 is represented by the equation as }

Fe + O

_{2}→ Fe_{2}O_{3.}
The above equation is not a balanced one. In many cases skeleton equation is not a balanced one.

For example ;

SnO

_{2 }+ H_{2 }→ Sn + H_{2}O
The above equation is not a balanced one. So we must balance the equation by balancing coefficients before the various molecules and to ensure the number of atoms on the left side of the arrow corresponds exactly to the number of elements on the right.

In this case, two oxygen atoms on the left hand side of the equation and only one atom on the write hand side of the equation. So we putting a coefficient of 2 in front of water.

SnO

_{2}+ H_{2 }→ Sn +2 H_{2}O
Now check the equation is not a balanced one.Because 2 hydrogen atoms on the left hand side and 4 hydrogen atoms on the right hand side.Add coefficients of 2 for left hand side of the hydrogen.

SnO

_{2}+ 2H_{2 }→ Sn +2 H_{2}O
After balancing and adjusting coefficient, we check the equation is a balanced one. Each side of the equation has 1 Sn atom, 4 Hydrogen atom, 2 Oxygen atom.Finally we specifying the states of matter.

The final equation also indicates the physical state of each substance. The abbreviation are used in these states are,

Solid (s)

Liquid (l)

Gas (g)

Aqueous Solution (aq) .

In the above equation oxides are solid, hydrogen forms a diatomic gas, ton is a solid and water vapor indicates that water is in the gas phase.

SnO

_{2}(s) + 2H_{2}(g) → Sn (s) +2 H_{2}O(g)- Important conditions such as temperature, pressure, catalyst etc may be noted above or below arrow of the equation.Upward arrow indicate the gaseous product. Downward arrow indicate the precipitated product.

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