TM 13: Using english to calculate

Definition Stoichiometry

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.

In confusion huh? Okay, this is simple.
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 performing Stoichiometric calculations, 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 the same as 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 Loss Law: The mass of the product is equal to the mass of the reactants

Fixed Comparative Law (Proust Law)
Fixed Comparative Law: Chemical compound consists of chemical elements with the ratio of 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 persmaaan:
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.

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 or substance.

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.

The Concept of Moles and Molar Mass
In SI systems, one mole is defined as the sum of the material composed of entities (atoms, molecules, or other particles) a sum of the atoms in 12 grams of carbon-12. The value of the number of atoms called the  6,022×10²³  Avogadro number, NA.
The molar mass, defined as the mass of 1 mol entity (atom, ion, molecule, unit of formula) of matter. The unit of the molar mass is grams / mol.

Problems example:
Determine Molar Mass from H2O?
Answer:

2 (1.00794g / mol) + 1 (15.9994g / mol) = 18.01528g / mol
The molar mass of Hydrogen is 1.00794g / mol multiplied by 2 because there are two hydrogen atoms in one water compound. Then the molar mass of oxygen is added.
The obtained Molar mass can be used to calculate the mole of a compound. If there is not yet understand about mole please go to wikipedia about mole understanding.
The formula of the interest of the mole of the compound is:
Mol = m / Mr
with;
Mol : mol Compounds
m : Mass Compound (gr)
Mr : Molar Mass (Reality Mass).

Sample Problem Involving Chemical Stoichiometric Calculations

Propane burns by reaction equation:
C3H8 + O2 → H2O + CO2
If 200 g of propane is burned, then how much H2O is formed?

Completion:
 

First: Resolve the equation of the reaction!
C3H8 + 5O2 → 4H2O + 3CO2

Second: Calculate C3H8 mole!
Mol = m / Mr -> mol = 200 g / 44 g / mol -> mol = 4.54 mol

Third: Calculate the ratio of H2O: C3H8 -> 4: 1 (* based on the comparison coefficient on the equation of the reaction)

Fourth: Calculate the mole of H2O by comparison
Mol H2O: 4 = mol C3H8: 1
-> mol H2O: 4 = 4.54 mol: 1
-> mol H2O = 4.54 x 4 = 18.18 mol

Fifth: Convert from mol to gram.
Mol = m / Mr -> m = mol x Mr -> m = 18.18 mol x 18 = 327.27 grams.