Using English to Predict Rendement of Product a Reaction

Rendement 

Rendement is actually a term in the field of chemistry studies. The yield represents the inaccuracy of the reaction result, which results always lower than the mathematical calculation. For example, in a chemical reaction, should produce a substance weighing 100 grams, mathematically, but in reality the results obtained only 90 grams. Unconsciously this also often happens in our daily lives.

In chemistry, the chemical yield, the yield of the reaction, or only the rendement refers to the amount of reaction product produced in the chemical reaction. Absolute rendement can be written as weight in grams or in moles (molar yield). The relative yield used as a calculation of the effectiveness of the procedure, is calculated by dividing the amount of product obtained in moles by the theoretical yield in moles:

To obtain a percentage yield, multiply the fractional yield by 100%.

One or more reactants in chemical reactions are often used redundantly. The theoretical rendement is calculated based on the number of moles of the limiting reagent. For this calculation, it is usually assumed that there is only one reaction involved.

The ideal chemical yield value (theoretical rendement) is 100%, a value highly unlikely to be achieved in its practice. Calculate the percentage of rendement that is by using the following equations percent rendemen = weight yield / weight of yield divided by the sample weight multiplied by 100%.

In determining the direction of a chemical reaction we must rely on an understanding based on a number of factors, and contents that are not always easy to assess. Although the assessment is prone to error, it is usually reliable where it seems reasonable to try, and that is certainly to answer ignorance.

In predicting chemical reactions there are many known factors such as, if there is no problem predicting a chemical reaction. Then if only enthalpy changes are known, then predictions usually apply to room temperature but are more or less reliable as well for higher temperatures. If the reaction occurring in the solution and the oxidation potential of the compound is relatively simple, and this oxidation potential buys a rough guide for possible reactions in the absence of a solvent. If the equilibrium constant is known, relating to ΔG0 = - RH in K gives us a change of free energy. But information on this is still lacking, so we must rely on our understanding of the preceding principles.

For chemical reactions at the temperature of the reactants and the products are produced. Here are the rules that may be useful and will be used.

Reactions tend to occur where the bonds of the orbital and some of the electrons are available and allow for attractive tensile interactions between atoms.

There is a possibility of electrons to be divided, and it always happens with energy changes. Therefore we can predict that the atoms of the atoms under the applicable conditions produce the same or different elements. The only elements of the atomic forests are not contained atoms of low external energy ie: "inert" elements or helium groups. Even this, when the circumstances are created, so through the influence of highly electronegative elements such as fluorine can be united by chemical bonds.

When that possibility exists, the tendency of atoms to form temperatures, then at the temperatures, then on the outcome there is little influence from the circumstances. In predicting reactions at ordinary temperatures, we can consider the preceding principles or bond strength and seek the total bond strength in the reactants or products. On this basis we can make prediction rules for definite possibilities or on reactions.

All chemical reactions can be classified into one of six categories:

ü Burning Reactions

The combustion reaction is when oxygen combines with other compounds to form water and carbon dioxide. These reactions are exothermic, which means they produce heat. For example naphthalene combustion reaction. C10H8 + 12 O2 -> 10 CO2 + 4 H2O

ü Reaction Synthesis

The synthesis reaction is when two or more simple compounds combine to form one more complex compound. These reactions appear in a general form:

A + B -> AB

One example of a synthesis reaction is a combination of iron and sulfur to form iron (II) sulfide:

8 Fe + S8 -> 8 FeS

ü Decomposition Reactions

The decomposition reaction is the opposite of the synthesis reaction - the complex molecule is broken down to make a simpler molecule. These reactions appear in a general form:

AB -> A + B

One example of a decomposition reaction is electrolysis of water to make oxygen and hydrogen gas:

2 H2O -> 2 H2 + O2

ü Single Displacement Reaction

This reaction is when one element alternates with another in a compound. These reactions appear in a general form:

A + BC -> AC + B

One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Mg + 2 H2O -> Mg (OH) 2 + H2

ü Double displacement reaction

This is when the anions and cations of two different molecules switch places, forming two completely different compounds. These reactions appear in a general form:

AB + CD -> AD + CB

One example of a dual displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Pb (NO3) 2 + 2 KI -> PbI2 + 2 KNO3

ü Acid-base Reactions

This is a special kind of double displacement reaction that occurs when acids and bases react with each other. H + ions in acid react with OH⁻ ions in the base, causing water formation. Generally, the product of this reaction is ionic and water salts:

HA + BOH -> H2O + BA

An example of an acid-base reaction is the reaction of bromide acid (HBr) with sodium hydroxide:HBr + NaOH -> NaBr + H2O

The efficiency of a chemical reaction can be determined by calculating the percentage of results. Almost in all reactions, we will get fewer results than expected. This happens because most of the reactions are equilibrium reactions, or because of some reaction conditions that cause the reaction not to run perfectly. Chemists can obtain reaction efficiency by calculating the following percentage of results:

Percentage of results = (actual results / theoretical results) x 100%

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. For example, the theoretical result of ferrous metals is 699.47 grams. While the real result is 525 grams. Therefore, the percentage of the results is:

% Yield = (525 grams / 699.47 grams) x 100% = 75.05%

The 75% yield percentage is not a too bad result.

In some chemical reactions, the reactants provided do not always correspond to the 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 / NH3 coefficient = 5,874 / 4 = 1,468

Mol O2 = 100 gram / 32.00 gram.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: Mole NO = 5: 4

Mol NO = 4/5 x Mol O2 = 4/5 x 3.125 mol = 2.5 mol NO

Mass NO = mole NO x Ar NO = 2.5 mol NO x 30.00 gram NO / mol NO = 75.00 gram NO

The value of 75.00 grams of NO is the theoretical result. If the actual result is 70.00 grams, the percentage of the reaction product is (70.00 gram / 75.00 gram) x 100% = 93.33%.

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