Using English to Predict Rendement of Product a Reaction




In chemistry, it is often important to know how efficient a reaction is. This is because when a reaction is carried out, the reactants may not always be present in the proportions written in the balanced equation. As a result, some of the reactants will be used, and some will be left over when the reaction is completed.

Theoretical, Actual, and Percents Yields

A reaction should theoretically produce as much of the product as the stoichiometric ratio of product to the limiting reagent suggests. This number can be calculated and is called the theoretical yield. However, the amount of product actually produced by the reaction will usually be less than the theoretical yield and is referred to as the actual yield. This is because often reactions have "side reactions" that compete for reactants and produce undesired products.

To evaluate the efficiency of the reaction, chemists compare the theoretical and actual yields by calculating the percent yield of a reaction:

Percent yield = (actual yield/theoretical yield) ×100

To calculate percent yield using this equation, it is not necessary to use a particular unit of measurement (moles, mL, g etc.), but it is important that the two values being compared are consistent in units. The theoretical yield of a reaction is 100 percent, but this value becomes nearly impossible to achieve due to limitations.

To accurately calculate the yield, the equation needs to be balanced. Next, identify the limiting reagent. Then the theoretical yield of the product can be determined and, finally, compared to the actual yield. Then, percent yield can be calculated.

Example: In some chemical reactions, the provided reactant does not always correspond to its stoichiometric ratio. This means, we will run out of one of the reactants and still leave another reactant. The former reactant is known as a limiting reagent. The limiting reagent determines the amount of product to be produced by a chemical reaction. Here we will discuss how to determine the limiting reagents through the following example:

4 NH3(g) +  5 O2(g) →  4 NO(g) +  6 H2O(l)

We start with 100 grams of ammonia gas which is reacted with 100 grams of oxygen gas. Which reactants are limiting reagents? How many grams of nitrogen monoxide (NO) gas can be produced?

To determine which reactants are limiting reagents, we can use a ratio (mole ratio) to the reaction coefficient. We calculate the number of moles each and then divide by their respective reaction coefficients based on equations of equalizing chemical reactions. The ratio of moles to the smallest coefficients is a limiting reagent.

Mol NH3 = 100 gram/17,024 gram.mol-1 = 5,874 mol

Mol NH3/coefficient NH3 = 5,874/4 = 1,468

Mol O2 = 100 grams/32,00 grams.mol-1 = 3,125 mol

Mol O2/ coefficient O2 = 3,125/5 = 0,625

The ammonia gas has a ratio of mole to the coefficient of 1.468. Meanwhile, oxygen gas has a value of ratio of 0.625. Thus, oxygen gas is a limiting reagent. The calculation of the product to be produced depends on the oxygen gas mole.

The stoichiometric ratio of NO to O2 is 4: 5

Mol O2 :  Mol NO  =  Reaction coefficient O2 :  Reaction coefficient NO

3,125 : Mol NO = 5 : 4

Mol NO = 4/5 x Mol O2 = 4/5 x 3,125 mol = 2,5 mol NO

Mass NO = mol NO x Ar NO = 2,5 mol NO x 30,00 grams NO/mol NO = 75,00 grams NO
Value 75,00 grams NO is a theoretical result. If the real result is 70.00 grams, the percentage of the reaction product is equal to (70,00 grams/75,00 grams) x 100 % = 93,33%.

We can also calculate how much ammonia gas is left. The mole gas calculations of ammonia used in the reaction depend on the mole of oxygen gas as a limiting reagent.

The stoichiometric ratio of NH3 to O2 is 4 : 5

Mol O2 :  Mol NH3 =  Reaction coefficient O2 :  Reaction coefficient NH3

3,125 : Mol NH3= 5 : 4

Mol NH3 = 4/5 x Mol O2 = 4/5 x 3,125 mol = 2,5 mol NH3

Mass NH3 = mol NH3 x Ar NH3 = 2,5 mol NH3 x 17,024 grams NH3/mol NH3 = 42,56 grams NH3

Thus, the amount of ammonia gas remaining (not used) is as much as 100 grams - 42.56 grams = 57.44 grams.

Komentar

  1. Mutia19 Mei 2017 pukul 02.20

    What is the relation between percent yield and predicting product of a reaction?

    BalasHapus
    Balasan
    1. Nurul Rahmiah19 Mei 2017 pukul 04.51

      Product prediction is as expected, forecast or forecast how big the product produced from a reaction and percent of the results can be formulated actual results / Results in theory) x 100%. Well, percent of the results with product predictions are closely related.

      Hapus
  2. weni19 Mei 2017 pukul 02.21

    Could you give me definition of predict and rendemen ? . and Your opinion, what is the point we predict the rendement?

    BalasHapus
    Balasan
    1. Nurul Rahmiah19 Mei 2017 pukul 06.04

      Prediction is a guess what might happen based on observations and statements about what will happen or may happen in the future while the yield refers to the amount of reaction product produced in a chemical reaction. Rendement is used as a calculation of the effectiveness of the procedure.

      Hapus
  3. shabrina19 Mei 2017 pukul 04.19

    what is the called the theoretical yield?

    BalasHapus
    Balasan
    1. Nurul Rahmiah19 Mei 2017 pukul 05.19

      The theoretical result is how many products are obtained based on stoichiometric calculations.

      Hapus
  4. Anonim19 Mei 2017 pukul 05.08

    How to know how efficient a reaction is?

    BalasHapus
  5. Arifahrachel19 Mei 2017 pukul 05.15

    What is the difference between the theoretical results and the actual results?

    BalasHapus
    Balasan
    1. Nurul Rahmiah19 Mei 2017 pukul 05.24

      The real result is how many products are obtained after the reaction is over. The theoretical result is how many products are obtained based on stoichiometric calculations. The comparison of these two results provides an explanation of how efficient the reaction is.

      Hapus
  6. Unknown21 Mei 2017 pukul 07.37

    What causes some reactants to lag when the reaction is over?

    BalasHapus

Posting Komentar

Postingan populer dari blog ini

Video: Rahmi's final assignment (Group 7-The Halogens)

Gambar
  Group 7-The Halogens Please watch my video: https://youtu.be/Fx7bkOz9Uko Group 7 – the halogens The Group 7 elements are called the halogens. They are placed in the vertical column, second from the right, in the periodic table. Chlorine, bromine and iodine are the three common Group 7 elements. Group 7 elements form salts when they react with metals. The term ‘halogen’ means 'salt former'. Properties and uses of the halogens This table summarises some of the properties and uses of three halogens: Element Properties Typical use Chlorine Green gas Sterilising water Bromine Orange liquid Making pesticides and plastics Iodine Grey solid Sterilising wounds Iodine forms a purple vapour when it is warmed. Predicting properties The halogens show trends in physical properties as you go down the group. Melting point and boiling point The halogens have low melting poi...
Baca selengkapnya

Acid Rain (Causes and Effects)

Gambar
What is Acid Rain? Acid rain, or acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.  This can include rain, snow, fog, hail or even dust that is acidic.   What Causes Acid Rain?   Acid rain results when sulfur dioxide (SO 2 ) and nitrogen oxides (NO X ) are emitted into the atmosphere and transported by wind and air currents.  The SO 2 and NO X react with water, oxygen and other chemicals to form sulfuric and nitric acids.  These then mix with water and other materials before falling to the ground. While a small portion of the SO 2 and NO X that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels.  The major sources of SO 2 and NO X in the atmosphere are: Burning of fossil fuels to generate electricity. ...
Baca selengkapnya

Halogen (compare and contrast between Fluorine and Bromine)

Gambar
HALOGEN As we know the element of group 7A produce salts with metals, so they are called halogen, from a greak word halos- genes, meaning   “salt former”. This group contains fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). Astatine is radioactive element. Halogen have 7 valence electrons. Since their atomic number are less than that of the following noble gases by one, they have -1 oxidation state in their stable compounds. Florine has only -1 oxidation state in its compounds. Florine is the most electronegative element of the periodic table. Within this group the electronegativity decreases from fluorine to iodine. Halogen are the element with the highest electronegativity in each period, so halogens are the most active nonmetals of each period. Figure 1. group 7A. halogens Physical properties Halogen are found as diatomic molecules in nature, such as F 2 , Cl 2 , Br 2 , I 2 . They are unstable in their   monoatomic forms. In the d...
Baca selengkapnya