PREDICTING RENDEMENT OF PRODUCT A REACTION

Predicted The Product Of Chemical Reaction

To write a simple document, some reliable rules are needed to assess the direction of a chemical reaction. And this judgment depends on several factors.

1. If free energy is known, there is no problem in prediction.

2. If only known enthalpy changes, predictions usually apply to ordinary temperatures are cheaper reliable for higher temperatures.

3. If any of them can be affected, the prediction is relatively simple and potential can be overcome in the possibility of reaction in the absence of solvent.

4. If the equilibrium constant is known, the relationship, G = - RH ln K gives free energy change, or reaction at ordinary temperatures where the entropy changes are not expected to be large, its relative strength in the reactants and the product can be estimated as a guide for the course of the reaction. On this basis, we may use this rule:

Principle 1: chemical reactions that occur with the bonds of electrons and electrons that can be used together and allow the interaction of attraction between atoms.

         The electron sac allows it to be shared then it always goes on with energy changes. We may be able to predict with confidence that all the atoms possessed or the outer orbital that is emptied will join at a limit or capability below the average of either the same element or different elements. Only the elements whose atoms are not incorporated under normal conditions are the atoms that do not contain the vacuum of their low external energy are called elements of iner or helium classes.

Principle 2: two elements can bond if the bonds formed are stronger than the average bond in a free state.

For example, the reaction between Cl2 and P. Cl2 in a stable state has an atomization energy of 29 kk / g atoms. The phosphorus atom is joined in a large set of molecules in which each atom joins to three different covalent bonds where the heat or atomisation strength is about 80kk / g of atoms. But it is easily disconnected by PCl3 molecules. The heat of PCl3 formation is 26 kcal / ek. The difference remains small, if all P and Cl2, whose atoms are separately like monoatomic gases, will join together to form P (s) and Cl2 (g), or bind to form a PCl3 molecule.

         When the atoms in each compound retain the power to stay together, the compound form will produce very strong strong binders if sufficiently polar. The same factor that affects tungsten, for example, possesses very high atomisation heat which allows the elements to form highly stable polar compounds, so that the energy lost in separating the tungsten atoms is very large from the energy retrieval when it joins with atoms such as halogens.

            But when the elements have the same electronegativity, the bond between the different elements of its polarity will be weak and if the strength does not have to be very strong of each element. For example, on the oxides of N it is not easily formed by comparison which is not stable. The heat of formation follows NO = 21.6; NO2 = 8,1; N2O = 19.5; N2O3 = 20.00; N2O4 = 2,30; And N2O5 = 3.6 kcal / mol.

Principle 3: Two molecules or ions tend to join if one pair of outer electrons can be shared with atoms that have empty orbitals.

In reaction with a very large atomic number known to the reaction type. This includes the linear arrangement of all the molecules at the addition of components, the joining of two simple components to form a component compound, and addition poli- lesation (this type occurs with the addition of joint molecules, in the absence of spiliting of some other products). This principle leads to a relatively stable incorporation.

Example:

                        CaO + SO3 → CaSO4

CaO is a very stable element, with the heat of atomization of 254 kcal / mol. However, having a relatively high negative partial, so that O in CaO includes a good donor potential. The three O bound to S, have less donor capacity, but enough to allow S to be bound to CaO. As a result, the O negative binds to S forming SO4. The heat of CaSO4 standard formation is 342 kcal / mol, in contrast to CaO 152kcal / mol, and SO3 95kcal / mol, otherwise summed only 247 kcal / mol.

In general, all negative charged oxides are effective as donors which provide electrons for the acceptor. The acceptor must have a high electron-electron attraction of the positive atoms on the donor oxide. For example, Na (0.40 charge) in NaO2 to receive electrons from O in CaO will be more attracted towards Ca because Ca has a load of 0.57 so it has a strong appeal of Na. In addition, there will be no tone of combining the two oxides as in N2O5 and SO3 because none of the O is negative enough as an effective donor.

Finally, acknowledged amphoteric oxides such as water may act as donor and acceptor in a reaction, depending on the character of the other oxide. This reaction tends to occur between halides (especially F) and sufides, with sulfides as metals and non-metallic halides. For example, on the formation of halide and sulfide complexes.

                       

CaCl2 + 6 H2O → CaCl2.6H2O

This type of reaction depends on the ability of O on water to provide electrons, better than chloride ions, with the previous assumption that O has more electron pairs than chloride ions. Water molecules can bind to calcium ions. A similar reaction will not proceed with kcl because K is of large size and weak nucleus load, so it is less effective as electron-electron binder.

All synthesis and adisin reactions take place with the reduction of entropy and therefore less able to take place with the addition of temperature. At high temperatures where the entropy goes beyond the enthalpy, it is more likely that a decomposition reaction occurs

Principle 4: An element tends to move to another of a compound if more than 1 polar bond is produced.

This principle indirectly describes the exchange of places between less active metals and very active metals. For example, Na can replace Al instead of Cl and, more and more easily replace H from water. However this only seems to imply a positive action from Na. It is very accurate to recognize the tendency of the embodiment of chlorine and O to have a high negative charge.

Principle 5: A large trend is for metathesis reactions to aid the arrangement of most polar bonds.

Some examples of synthesis of organometallic compounds from halides with highly electronegative metals and organometallic compounds with highly active metals.

HgCl2 + 2CH3MgCl → Hg (CH3) + 2MgCl2

A very polar bond exists between Mg and Cl, with charge Cl -0.17 in HgCl2 and -0.34 in MgCl2. Hydrolysis of binary compounds is common, non-metals with low electronegative nonmetals or metals.

NaH + H2O → 2NH3 + NaOH

Osigen is a element with very large electronegative being very negative in OH - (- 0.67) than in H2O (-0.25). The Mg-O bond is very polar.

Mg3N2 + 6H2O → 2NH3 + 3Mg (OH) 2

The type or reaction that is often used as a prediction depends on:

- Synthesis: The direct combination of elements or compounds

- Substitution: Transfer of one element or compound from a complex by another element or compound.

- Metathesis: Double composition or exchange of pairs.

Synthesis

      When all elements are almost different in electronegativity, the bonds between two different elements tend to be polar. Polar bonds tend to be stronger than non-polar bonds. The bonds between the two different elements tend to be very strong on average or bond in free elements. The heat of the formation of the binar compound is so large that it is negative (exothermic), and in general the greater the difference in the electronegativity and the bonded polarity results.

Substitution

      The relationship between bonding polarity and bond strength can be used only on general estimates because it ignores other factors such as bonding arrangements and bond lengths. Thus, this principle can be used entirely when other factors do not vary widely. In particular, the keelektronegatifity of a unsure if large will tend to have a high negative charge. In essence, the description of this principle tends to the degree of electronegativity for the turn of the element having the weak electronegativity of the component with the electron. The degree of electronegativity strength can be seen at: I <Br <Cl <F. Or by other conversion of hydride, sulfide, bromide, nitride, and iodod with heating in water.

Metathesis

          Metathesis is caused by a polar bond which is usually the strongest bond. This should meet:

1) most polar bonds are not necessarily very strong though often very strong,

2) the reaction does not have to occur in the strongest bond or the most stable compound, because sometimes free energy can be released when the compound is very stable and the less stable compounds exchange charge to form two new compounds with intermediate stability but above the average of the reactants . However, this rule is very useful although limited to many types of chemical charge is very important.

          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 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

Example

Stoichiometry - rendemen?
Commercial acetic acid (97% C2H4O2) reacted with excess PCl5 will produce acetyl chloride (C2H3OCl). If the acetyl chloride produced is 75 g and the reaction efficiency (rendement) 78.2%, then the amount of acetic acid reacted is ..

The answer: 97% = 0.97
78.2% = 0.782

Rendmen = yield yield / theoretical rendement
0.782 = 75 / theoretical rendement
Theoretical rendemen = 75 / 0.782
Theoretical rendement = 95.9 gr

The resulting theoretical yield of acetic acid was 95.9 gr

Percent of acetic acid = 97% = 0.97
Mean, acetic acid = 05.9 x 0.97
Acetic acid = 93 grams

Thus, the amount of acetic acid treated was 93 grams