Basic Chemical Stoichiometric Material

Understanding Stoichiometry

Stoichiometry comes from two Greek syllables Stoicheion meaning "element" and Metron which means "measurement".

Stoichiometry is a subject in chemistry involving the linkage of reactants and products in a chemical reaction to determine the quantity of each reacting agent.

More easily,

   "Stoichiometry is a subject in chemistry that studies the quantity of matter in a chemical reaction."


If there is a chemical reaction, you may want to know how many substances the reaction results? Or if you want to do a chemical reaction to produce a certain amount of product, then you have to adjust how many reactants in the reaction. These are all discussed in stoichiometry.

Before doing Stoichiometric calculations, the equation of the reaction we have must be equalized first. Before doing the calculation of Stoichiometry, the equation of the reaction we have must be equalized first.

Equalization of Chemical Reaction

Chemical reactions are often written in bentu equations using element symbols. The reactants are the substances that are on the left, and the product is the substance that is on the right, then both are separated by arrows (can be one or two alternating arrows). Example:  

2Na(s)+HCl(aq)→2NaCl(aq)+H2(g)

The equation of a chemical reaction is like a prescription in the reaction, thus indicating everything associated with the reaction, whether it is an ion, an element, a compound, a reactant or a product. All.

Then as in the recipe, there is a proportion of the equation shown in the figures in front of the molecular formula.

When considered again, the number of H atoms on the reactant (left) is not equal to the number of H atoms on the product (right). Then this reaction needs to be synchronized. The equalization of chemical reactions must satisfy some chemical laws of matter.

The Law of Conservation of Mass

Mass Losing Law: The mass of the product is equal to the mass of the reactants

Fixed Comparative Law (Proust Law)

  Fixed Comparison Law: The chemical compound consists of chemical elements with the ratio of the mass of elements that remain the same.

The Law of Multiple Comparisons (Dalton's Law)

  The Law of Multiple Comparisons: If an element reacts with other elements, then the ratio of the weight of the element is a simple integer

So from the equation: 

2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g)

We can know that 2 moles of HCl react with 2 moles of Na to form 2 moles of NaCl and 1 mole of H2. By equalizing this reaction, it can be known the quantity of each substance involved in the reaction.

Hence the equalization of this reaction is very important in solving stoichiometric problems.

Example:

Lead (IV) Hydroxide reacts with Sulfuric Acid, by reaction as follows:

Pb(OH)4+H2SO4→Pb(SO4)2+H2O

If we look good either:

Unsur	Reaktan (jumlah mol)	Product  (jumlah mol)
Pb	1	1
O	8	9
H	6	2
S	1	2

Then this equation is not equivalent. Therefore we need to equate this equation. In the reactant there are 16 atoms, but on its products there are only 14 atoms. This equation needs to add coefficients so that the number of atoms of the elements is the same.

In front of H2SO4 it is necessary to add coefficient 2 so that the number of sulfur atoms corresponds, then in front of H2O it is necessary to add coefficient 4 so that the number of oxygen atoms is appropriate. Then the equivalent reaction is:

Pb(OH)4+2H2SO4→Pb(SO4)2+4H2O

Unsur	Reaktan (jumlah mol)	Product  (jumlah mol)
Pb	1	1
O	12	12
H	8	8
S	2	2

The condition in which the equation of the reaction is equal is when it satisfies the following two criteria:

1.The number of atoms of each element on the left and right sides of the equation has been the same.

2.The number of ions on the left and right has been the same (using redox reaction equation)

Stoichiometric Calculations on Equivalent Chemical Equations

In stoichiometry, an equivalent chemical equation provides information to compare each element in a reaction based on a stoichiometric factor. The stoichiometric factor is the ratio of the moles of each reacting substance / substance.

In real life, this is an example:

To make a delicious cup of coffee, a recipe is required that is 9 cube sugar with 3 tablespoons of coffee.

Stoichiometric illustration in Life

This is a fix and patent recipe. So what if we have 12 sugar cubes and three spoons of coffee powder, how many cups of coffee can be made?

Yes! The answer is 1 cup of coffee, with the remaining ingredients 3 sugar.

How about we have 27 sugars and 8 spoons of coffee. How many cups of coffee can be made?

Of course 2 cups of coffee with the remaining 9 sugar and 2 coffee spoons. All absolutely must follow the recipe.

The key is that all must follow the prescription, if in stoichiometry, the equivalent reaction equation is the recipe, so we must follow the recipe.

Understanding Molar Mass

Before performing stoichiometric calculations, we need to know what a molar mass is. The molar mass is the ratio between the mass and moles of an atom.

To know the Molar Mass of an element then we only need to read it in the periodic table of elements. As for knowing the Molar Mass compound we need to calculate it based on the molecular formula of the compound.