Using English To Predict Rendement of Product a Reaction

In chemistry, yield, also referred to as reaction yield, is the amount  of product obtained in a chemical reaction. The absolute yield can be given as the weight in grams or in  moles (molar yield). The percentage yield (or fractional yield or relative yield), which serves to measure the effectiveness of a synthetic procedure, is calculated by dividing the amount of the obtained desired product by the theoretical yield (the unit of measure for both must be the same):

The first step---identifying the type of reaction involved---is usually the most difficult. The primary reaction types students encounter are displacement, acid-base and combustion. They are easily identified if the tell-tale signs are known. Displacement reactions involve two ionic compounds with cations and anions, such as sodium sulfate, in which sodium (Na?) is the cation and sulfate (SO?²?) is the anion. Ionic compounds always consist of a metal and a nonmetal or polyatomic (multiple-atom) anion. Decomposition reactions involve a single compound breaking into two or more compounds. Acid-base reactions must involve an acid (identified by its chemical formula that begins with “H,” such as HCl). Combustion reactions involve hydrogen or a hydrocarbon (such as CH?) reacting with oxygen (O?).

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 vachieved 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%

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

1. 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

2. 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

 3. 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

4. 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

5. 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

6. 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:HCl + NaOH -> NaCl + H2O

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.

The theoretical yield is the amount predicted by a stoichiometry calculation based on the number of moles of all reactants present. This calculation assumes that only one reaction occurs and that the limiting reactant reacts completely. However the actual yield is very often smaller (the percent yield is less than 100%) for several reasons:

·       Many reactions are incomplete and the reactants are not completely converted to products. If a reverse reaction occurs, the final state contains both reactants and products in a state of chemical equilibrum.

·     Two or more reactions may occur simultaneously, so that some reactant is converted to            undesired   by-products.

·     Losses occur in the separation and purification of the desired product from the reaction mixture.

·    Impurities are present which do not react