Question

Define a reversible reaction. Give an example.

Short answer

Answer: A reversible reaction is a chemical reaction where reactants can convert into products and products can convert back into reactants, reaching a state of equilibrium. An example is the esterification reaction between acetic acid (CH3COOH) and methanol (CH3OH), which form methyl acetate (CH3COOCH3) and water (H2O). The reverse reaction, hydrolysis, involves the ester and water reacting to regenerate the original acid and alcohol.

Step-by-step solution

Definition of a Reversible Reaction

A reversible reaction is a chemical reaction in which the reactants can convert into products and the products can convert back into the reactants. These reactions generally reach a dynamically stable state, called equilibrium, where the rates of the forward and reverse reactions are equal.

Providing an example

An example of a reversible reaction is the esterification reaction between an acid and an alcohol to form an ester and water. The reverse reaction is called hydrolysis, in which an ester and water react to form the corresponding acid and alcohol. The reaction is written as: \[CH_3COOH (acetic\;acid) + CH_3OH (methanol) \rightleftharpoons CH_3COOCH_3 (methyl\;acetate\;or\;ester) + H_2O (water)\] In this reaction, the reactants acetic acid (CH_3COOH) and methanol (CH_3OH) combine to form the ester (CH_3COOCH_3) and water (H_2O). Similarly, the ester and water can react together to regenerate the original acid and alcohol. The two-sided arrow (\(\rightleftharpoons\)) in the equation represents the reversible nature of the reaction.

Key concepts

Chemical Equilibrium

When discussing a reversible reaction, the term chemical equilibrium is vital. Chemical equilibrium represents a state in a reversible chemical process where the rates of the forward reaction (reactants converting to products) and the backward reaction (products converting to reactants) are equal. At this point, no net change in the concentration of reactants and products occurs even though the reactions continue to take place.

It's crucial to understand that reaching equilibrium doesn't mean the amounts of reactants and products are equal, but that their concentrations no longer change with time. This dynamic but stable situation is essential for many natural processes and industrial applications, such as the synthesis of chemicals.

Esterification

Esterification is an organic chemical reaction that leads to the formation of an ester. It typically involves the reaction of a carboxylic acid, like acetic acid, with an alcohol, such as methanol, in the presence of an acid catalyst. The product of this reaction is an ester and water, as demonstrated in the given example with methyl acetate being formed.

This reaction is of considerable importance in both academic and industrial contexts because esters are widely used as solvents, fragrances, and intermediates in the synthesis of various other compounds. Esterification is a prime example of a reversible reaction, as the ester produced can undergo hydrolysis to regenerate the original acid and alcohol.

Hydrolysis

Hydrolysis is the reverse process of esterification. In this reaction, water reacts with an ester, leading to the formation of a carboxylic acid and an alcohol, essentially breaking the ester bond.

This type of reaction is critical in many biological processes where it's important for the digestion and metabolism of complex molecules. In the context of the reversible reaction given in the exercise, hydrolysis is an example of how the products of the esterification, the ester, and water, can be converted back into the original reactants, acetic acid, and methanol.

Dynamic Stability

Dynamic stability in the context of chemical reactions refers to the state achieved when a reversible reaction reaches chemical equilibrium. Despite appearing static, the equilibrium state maintains constant activity where reactants and products are interconverted at equal rates.

This balance is not a result of ceased activity but a perfect compensation of changes, just like two teams in a tug of war pulling with equal and opposite force. In the exercise's chemical reaction, dynamic stability is reached when the forward esterification and the reverse hydrolysis occur at the same rate, leading to no observable change in the concentrations over time.