using english to calculate OF CHEMICAL STOIKIOMETRI

CALCULATION OF CHEMICAL STOIKIOMETRI

CALCULATION WITH CHEMICAL RESUME

AND EQUATION REACTIONS

One important aspect of chemical reactions is the quantitative relation between substances involved in chemical reactions, either as reagents or as a result of the reaction. Stoichiometry (stoi-kee-ah-met-tree) is a field in chemistry involving quantitative relationships between substances involved in chemical reactions, either as reagents or as a reaction product. 

Stoichiometry also involves the ratio of atoms between elements in a chemical formula, for example the ratio of the H atoms and the O atoms in the H2O molecule. The word stoichiometry comes from the Greek word stoicheon which means element and metron which means measure. A French chemist Jeremias BenjaminRichter (1762-1807) was the man who first laid down the basic principles of stoichiometry.

Why should we study stoichiometry? One reason, because studying chemistry can not be separated from doing experiments in the laboratory. Sometimes in our laboratory we have to react a number of grams of substance A to produce a number of grams of substance B. 

 Stoichiometry is closely related to chemical calculations.

To solve the problem of chemical calculation, the stoichiometric principles are

used, they are chemical equation and mole concept. In this lesson we will learn 

first about the principles of stoichiometry, then after that we will study

stoichiometric application on chemical calculations along with examples 

of problems and how to solve them.

The concept of a mole can be used to determine the chemical formula of 

a compound, both an empirical formula (the smallest comparison of 

atoms in a compound) and a molecular formula (number of atoms in a compound). 

1. Empirical formula, is the formula that gives the smallest comparison of 

the elemental atoms that make up each molecule of a compound2. The molecular 

formula is a formula that states exactly the atomic elements that make up 

each molecule of a compound.

Example: Compound Empirical formula Molecular formula
           Water        H2O           H2O
           Benzene      CH             C6H6
           Glucose      CH2O          C6H12O6
           amoniak      NH3           NH3 

The empirical formula can be determined by knowing the mole ratio of the elements that constitute a

 compound. Whereas the molecular formula can be determined if the empirical formula and the relative 

molecular mass (Mr) of the compound are known.

The atomic ratio of the elements in a chemical formula is indicated by a round number, and not by a

 fractional number. For example, carbon monoxide (CO) has a ratio between C atoms and O atoms 

equal to 1: 1, which means the ratio of atoms to make 1 molecule of CO without any residual

 atom C or O atom we must take 1 atom C and 1 atom O according to The ratio of the atoms

 in the chemical formula of the compound.1 atom C + 1 atom O → 1 molecule CO To make 1 dozen CO molecules,

 we must take 1 dozen C atoms and 1 dozen O atoms according to the 1: 1 atomic ratio.

 1 dozen atoms C + 1 dozen atoms O → 1 dozen CO moleculesTo make 1 gross (144) CO molecule,

 the equation would be:1 gross atom C + 1 gross atom O → 1 gross molecule COSo any unit of number 

of atoms used, most important is the ratio of atoms C and the same O atom, ie 1: 1.

 According to Avogadro:"Gases of the same volume, if measured at temperatures and pressuresSame,

will have the same number of molecules ".

Therefore the ratio of the volume of hydrogen gas, oxygen gas, and water vaporIn the reaction 

of moisture formation = 2: 1: 2 then the ratio of the number of moleculesHydrogen, oxygen, 

and water vapor are also 2: 1: 2. The number of atoms of each element is notDecreases or increases 

in chemical reactions.

2. Avogadro's Mix and Fixed ConceptWhen you react one carbon atom (C)

with one molecule of oxygen (O2) it will form one molecule of CO2.

But actually what you react is not a single carbon atom with one molecule of oxygen,

but a large number of carbon atoms and a large number of oxygen molecules. 

Since the number of atoms or the number of molecules reacting is so great then to say it, 

the chemists use "mol" as the unit of the number of particles (molecules, atoms, or ions).

Gas Volume in Non-Standard StateCalculation of gas volume is not in the standard state (non-STP) 

used the following two approaches. A. The ideal gas equationAssuming the gas

to be measured is ideal, the equation that links the number of moles (n) of gas,

pressure, temperature, and volumethat is:

The ideal gas law:

P. V = n. R.

TWhere:

 P = pressure (atmospheric unit, atm)

 V = volume (liters, L)

 N = number of moles of gas (mol unit) R = gas constant (0.08205 L atm / mol K)

 T = absolute temperature (° C + 273.15 K)

With gas conversion at the same temperature and pressureAccording to Avogadro's law, 
the ratio of gases having the same number of moles has the same volume. Mathematically 
can be expressed as follows.V1 / V2 = n1 / n2Where:N1 = mol gas 1 V1 = gas volume
1N2 = mol gas 2 V2 = gas volume 2 4. Molarity (M)The amount of substances present
in a solution can be determined by using the concentration of the solution expressed 
in molarity (M). Molarity states the number of moles of substances in 1 L of solution. 
Mathematically stated as follows.Where:M = molarity (unit M)Mass = in units 
gMr. = molar mass (unit g / mol)V = volume (mL unit).

D. Molecular Formulas and Elemental Content in Compounds

The ratio of mass and elemental content in a compound can 
be determined from its molecular formula.
1. Determination of Empirical Formulas and Molecular Formulas
The chemical formula shows the atomic type of element and the 
relative amount of each element contained in the substance.
 The number of substances contained in the substance isindicated by the index number.
The chemical formula can be an empirical formula and a molecular formula.
"Empirical formula, the formula which states the smallest comparison of atomatoms
Of the elements that make up the compound ".
"The molecular formula, the formula yamg states the number of atoms of
The elements that make up one molecule of the compound ".
Molecular formula = (Empirical formula) n
Mr. Molecular formula = n x (Mr. Empirical Formula, N = integers
The determination of the empirical formula and the molecular 
formula of a compound can be achieved by the following steps.
1. Find the mass (percentage) of each constituent compound,
2. Change to mole unit,
3. The mole ratio of each element is an empirical formula,
4. Find the molecular formula by: (Mr. empirical formula)
 n = Mr. molecular formula, n can be calculated,
5. Multiply n obtained from the count by the empirical formula.

A compound comprises 60% carbon, 5% hydrogen, and the remainder is nitrogen.

 Mr. compound it = 80 (Ar: C = 12; H = 1; N = 14). Determine 

the empirical formula and the molecular formula of the compound!

Answer:

Percentage of nitrogen = 100% - (60% + 5%) = 35%.

Suppose the mass of the compound = 100 g

Then mass C: H: N = 60: 5: 35

Comparison of mol C: mol H: mol N = 5: 5: 2,5 = 2: 2: 1

Then the empirical formula = (C2H2N) n. (Mr. empirical formula)

 n = Mr. molecular formula

(C2H2N) n = 80

(24 + 2 + 14) n = 80

40n = 80

N = 2

Thus, the molecular formula of the compound = (C2H2N) 2 = C4H4N2.

3.  Chemical Count

The determination of the amount of reactants and the reaction products involved in the

 reaction must be calculated in units of moles. That is, the units that are known must be 

converted into mol form. This method is called the mole approximation method.

4. Pereaksi Pembatas

In a chemical reaction, the mole ratio of the mixed reagents is not always the same as the 

ratio of the reaction coefficient. This means that there are reagents that will run out first.

Such reagents are called limiting reagents. How can this happen?

X + 2Y -> XY2

The above reaction shows that according to the reaction coefficient, one mole of X takes two moles of Y.
 The above figure shows that three molecules of X are reacted with four molecules 

of substance Y. After the reaction takes place, the number 

of X-substance molecules reacting only two molecules and one Molecule left.

 Meanwhile, four Y-substance molecules are reacting. Then this Y 

substance is called a limiting reagent. The limiting reagent is a 

reactant that reacts and does not remain at the end of the reaction. 

In chemical counts, the limiting reagents can be determined by dividing 

all the moles of the reactant by their coefficients, then the reactants 

having the smallest yield value being the limiting reagents.problems 

example Known reaction as follows S (s) + 3F2 (g) -> SF6 (g).If reacted 

with 2 mol of S with 10 moles of F2, determine:A. How many SF6 mols are formed?


S + 3F2 –> SF6
S + 3F2 -> SF6 

From the reaction coefficient shows that 1 mol of S requires 3 moles

of F2. The possibilities are as follows.A. If all S reacts then F2 

is required:This is possible because F2 is available 10 mol.