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Forward Reaction

In a chemical reaction the two very important aspects are how fast the reaction is occurring and to what extent the reaction going to completion. The description of these extents is often defined in terms of whether the reaction is moving forward or to the right or backward or to the left. The forward and backward reactions have their own limitations and advantages along with several conditions that apply.

In any chemical reaction when the reactants react with each other under specific conditions like temperature, pressure and catalysts to form the products we conclude the direction of reaction as forward. In chemical reactions where equilibrium is reached and considered under reversible then the products thus formed become the reactants for the backward reaction. In irreversible chemical reactions the change could be attributed only for forward direction as conditions do not apply for the reaction to turn back and form the reactants.

A + B $\leftarrow \rightarrow $ C + D

Where A and B are reactants in the forward (towards right) reaction and once the equilibrium is reached C and D becomes the reactants for the backward (towards left) reaction. In many chemical changes, reactants are converted partially only. In such reactions, the concentration of both reactants and products remain constant when a particular stage is reached and these reactions however in between forward and backward reactions. This is said to be the state of chemical equilibrium. During the state of chemical equilibrium the rate of forward and rate of backward reaction are said to be equal.

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Definition of Forward Reaction

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The definition of forward reaction for any chemical change would be about the reactants reacting and producing the products on the right side of the arrow. Any forward reaction would move to the right side where products or product is formed.

Theoretically almost all the chemical reactions are reversible and the reactants are formed back from products regularly. There are certain conditions which guide the forward reaction to reach equilibrium with the backward reaction and trigger the breaking down of products to get back the reactants.

What is Forward Reaction?

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The reaction which shows the direction of a chemical change towards the formation of products under specific conditions is better known as forward reaction.
  • The forward reaction could be enhanced if the concentration is increased or the pressure of the system is increased resulting in more collision rate and forming more products. The higher collision rate and more products show the forward reaction more vividly.
  • The increased range of temperature meanwhile results in breaking down of products which triggers the backward reaction forming the reactants.
  • There are other factors like rate constants for both forward and backward reactions. These rate constants are different for every chemical change.
  • Similarly when we consider the concentrations of the reactants, the higher the reactants concentration, the faster the reaction will go forward. As the concentration of reactants progressively reduces, the concentration of products increases gradually.
Once the chemical equilibrium is reached when the rates of forward and backward becomes equal, then reverse reaction takes over once the products breakdown and moves backward.

Since the depletion of reactants results in the formation of products during a chemical change, the forward reaction rate would decrease as well. With the decrease in forward reaction rate, the reverse reaction rate slowly goes up. These changes in both quantity and rate carry on till the reaction reaches a state of equilibrium when no net product formation takes place.
  • A forward reaction could be endothermic in nature where the temperature increase will shift the equilibrium towards right.
  • A forward reaction could also be exothermic in nature where the increase in temperature will shift the equilibrium of the chemical change from right to left side.

Examples of Forward Reaction

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When we consider the forward reaction of any chemical change we observe that in endothermic reactions the increased temperature of the system moves the reaction in a direction where this increased temperature could be negated.

While in chemical reactions which are exothermic in nature, lower temperature definitely favors the reaction to move forward or to the right.

N_{2} (g) + $O_{2}$ (g) $\leftarrow \rightarrow$  2 $NO(g)$

In the above mentioned reaction, the increase in temperature shifts the equilibrium towards right side and forms nitric oxide.

$PCl_{5}$ $\leftarrow \rightarrow$  $PCl_{3}$ + $Cl_{2}$ 

Here, phosphorus penta chloride decomposes into phosphorus tri chloride and chlorine.

CO (g) + $Cl_{2}$ (g) $\leftarrow \rightarrow$ $COCl_{2}$ (g)

Carbon monoxide reacts with chlorine gas to produce phosgene gas. Next we could discuss about Haber’s process where nitrogen gas reacts with hydrogen gas to produce ammonia. The reaction forward is exothermic in nature.

$N_{2}$ (g) + $3H_{2}$ (g) $\leftarrow \rightarrow$ $2NH_{3}$ (g)

The forward reaction is favored due to the higher concentration of reactants which tends to negate in a manner which helps in decrease the reactants concentration by producing more products.

2 $SO_{2}$ (g) + O2 (g) $\leftarrow \rightarrow$ $2SO_{3}$ (g)

4 HCl (g) + $O_{2}$ (g)  $\leftarrow \rightarrow$ 2Cl2 (g) + $2H_{2}O$ (l) 

Organic Reactions

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In organic reactions, each of the functional groups of organic molecules shows distinct patterns of reactivity. Organic reactions are classified on the basis of reaction mechanisms and thus we have polar reactions, pericyclic reactions and free radial reactions.

These organic reaction categories have own characteristics and the differentiation is based purely on the manner of mechanism and effects.

Polar reactions:
The polar organic reactions take place when the atoms which are bonded together dissociate and any one of these dissociated atoms carry larger share of electrons resulting in cation and anion. These cleavages are heterolytic in nature.

Free radical reactions:
Unlike the polar reactions these reactions involve radicals. When a molecule dissociate by homolytic cleavage it produces two of these radicals and although the radicals are uncharged the incomplete octet makes these very unstable and reactive. The instability is managed only after these radicals form a bond.

Pericyclic reactions:
These types of organic reactions are carried out by reorganizing the electron pairs of the bond simultaneously by cyclic transitions.
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