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USING ENGLISH TO CALCULATE (resume 5)

 STOICHIOMETRY
How to measure the amount of a compound contained in a material? This is a basic question that has been answered by the early chemists. They answer it with a chemical concept called Stoichiometry.

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. 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? 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 elemental 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
"The mass of the product is equal to the mass of the reactants"

Fixed Comparative Law (Proust 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) 
"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.

Ideal Gas Law
For an ideal gas or a gas that is considered to be valid applies the formula:
PV = n RT

\frac{P_1V_1}{n_1 RT_1} = \frac{P_2V_2}{n_2 RT_2}
Note:
P = pressure (atmosphere)
V = volume (liters)
N = mol = gram / Mr
R = gas constant (lt.atm / mol.K)
T = temperature (Kelvin)

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. 
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.
ilustrasi Stoikiometri dalam Kehidupan 
  
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 cube sugar. How about we have 27 sugar cube and 8 spoons of coffee. How many cups of coffee can be made? Of course 2 glasses of coffee with the remaining 9 sugar cube 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 equation of the reaction. 

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. 

CONCEPT MOL
In chemistry the unit of quantity used is mol
One mole is a number of substances containing 6.02 x 10 ^ 23 particles 

The relationship of Moles to the number of particles 
Number of Particles = mol x 6.02 x 10 ^ 23 
Mol = Number of particles / 6.02 x 10 ^ 23

Relation of Moles to Mass 
*For element:
  Mol = gram / Ar
  Gram = mol x Ar  
*For compounds:
  Mol = gram / Mr
  Gram = mol x Mr

Relation of Mole to Gas Volume
*Every mole of gas of any standard state (0oC, 1 atm) has a volume of: 22.4 liters.
  Volume of gas = mol x 22.4
  Mol = Volume / 22.4
Image result for materi lengkap stoikiometri bahasa inggris inggris 


Komentar

  1. Unknown1:43 AM

    Can you find the relative atomic mass of Mg (OH) 2?

    BalasHapus
    Balasan
    1. Aulia Rahmi4:22 PM

      Ar Mg = 24
      Ar O = 16
      Ar H = 1
      Mr Mg(OH)2 = (1 x 24) + (2 x 16) + (2 x 1)
      = 24 + 32 + 2
      = 58 g/mol

      Hapus
  2. Unknown2:14 AM

    How to apply the concept of stoichiometry?

    BalasHapus
    Balasan
    1. Aulia Rahmi4:37 PM

      In everyday life, we often encounter matters relating to stoichiometry, whether contained in nature, laboratories, industries or factories, and the environment around us. One example of stoichiometry in our environment for example, the food we consume every day after digested and converted into energy for the body. Another example is a housewife who has a hobby of planting orchids and other ornamental plants, he wanted to spray his favorite plants with direct fertilizer kedaunnya, this makes him have to make a solution with a certain concentration.

      As we can find for example, nitrogen and hydrogen combine to form ammonia which is used as fertilizer and fuel produced by petroleum, there are also some raw materials necessary if we want to obtain a certain amount or yield

      An example in an industry is a mining plant that can explain the quality of the ore, since the percent of the mass composition of the elements in the compound can be calculated rapidly. It is also included in the law of chemistry on the law of mass comparison.

      Hapus
  3. Unknown5:32 AM

    Hydrocarbons (CxHy) of 10cm3 in perfect burn with 20 cm 3 of oxygen gas and yield 10 cm 3 of carbon dioxide gas. If the gas is measured at the same temperature and pressure, determine the molecular formula of the compound?

    BalasHapus
    Balasan
    1. Aulia Rahmi4:33 PM

      At the same temperature and pressure, the ratio of volume = coefficient ratio.
      Equation of reaction
      CxHy + O2 ----> CO2 + H2O

      Volume ratio = 10: 20: 10
      = 1: 2: 1
      CxHy + 2 O2 ----> CO2 + 2H2O
      (the coefficient of H2O is obtained from equalizing the number of O)

      Number of C left = number of C right
      X = 1
      The number of H left = the number of H right
      Y = 4
      Then the molecular formula is CH4

      Hapus
  4. Yulia Saltiani5:50 AM

    A compound having the empirical formula CH 3. If Mr compound is 30, determine the molecular formulas of these compounds?

    BalasHapus
    Balasan
    1. Aulia Rahmi4:42 PM

      Ar C = 12
      Ar H = 3
      Empirical formula = Mr
      CH3 = 30
      (CH3) n = 30
      12n + 3n = 30
      15n = 30
      n = 30/15
      n = 2
      So the molecular formula is C2H6

      Hapus
  5. Unknown3:19 PM

    If 1 liter of gas NO mass 1 gram, how many grams of 2 liters of O2 gas if measured at the same temperature and pressure?

    BalasHapus
    Balasan
    1. Aulia Rahmi4:51 PM

      At the same pressure and temperature, apply:
      Mol NO: volume NO = mol O2: O2 volume
      (1/30): 1 = mol O2: 2
      Mol O2 = 2: 30
      Mass O2 = mol O2 x Mr. O2
      Mass O2 = (2/30) x 32 = 2,134 grams

      Hapus

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