EQUILIBRIUM IS SAID TO BE ATTAINED IN REVERSIBLE REACTION WHEN

• A. all the reactants have been used up
• B. all the products have been formed
• C. there is no further change in temperature
• D. the rates of the forward and backward reactions are equal ✓
• E. the rate of formation of the products decreases with time

The answer to the question is: D. the rates of the forward and backward reactions are equal

In a reversible reaction, equilibrium is said to be attained when the rate of the forward reaction is equal to the rate of the reverse reaction. This means that the concentrations of the reactants and products remain constant over time, although they are constantly interconverting. At equilibrium, the system appears to be static, with no observable changes in the macroscopic properties of the system.

Characteristics of Equilibrium in Reversible Reactions

1. Dynamic Nature: Equilibrium in reversible reactions is dynamic, meaning that while there is no net change in the concentrations of reactants and products, individual molecules are continuously reacting and interconverting between reactants and products.
2. Constant Concentrations: At equilibrium, the concentrations of reactants and products remain constant. However, it’s important to note that this does not mean that the concentrations are equal; rather, they stabilize at specific values determined by the equilibrium constant for the reaction.
3. Reversible Reaction: In a reversible reaction, both forward and reverse reactions occur simultaneously. At equilibrium, the rates of these two opposing reactions are equal.
4. Physical Properties: The physical properties of a system at equilibrium remain constant. For example, if a reversible reaction involves gases, the pressure will remain constant at equilibrium.
5. Equilibrium Constant: The equilibrium constant (K) expresses the ratio of product concentrations to reactant concentrations at equilibrium for a chemical reaction. It is a reflection of the extent to which a reaction favors either the products or reactants at equilibrium.

Factors Affecting Equilibrium in Reversible Reactions

Several factors can affect the position of equilibrium in a reversible reaction:

1. Concentration: Changes in the concentration of reactants or products can shift the position of equilibrium. According to Le Chatelier’s principle, if the concentration of a reactant is increased, the system will shift to consume some of that reactant and produce more products until a new equilibrium is established.
2. Pressure: For gaseous reactions, changes in pressure can affect equilibrium. If pressure is increased, the system will shift to reduce it by favoring the side with fewer gas molecules.
3. Temperature: Altering temperature can also impact equilibrium. In an endothermic reaction (absorbs heat), increasing temperature will shift the equilibrium position towards the products, while in an exothermic reaction (releases heat), increasing temperature will favor the reactants.
4. Catalysts: Catalysts do not affect the position of equilibrium but can speed up both forward and reverse reactions equally, allowing equilibrium to be reached more quickly.

Conclusion

In summary, equilibrium in reversible reactions occurs when there is a balance between the rates of the forward and reverse reactions, resulting in constant concentrations of reactants and products over time.