Reversible reactions achieve equilibrium when the rates of the forward and reverse reactions are equal.

In a reversible reaction, reactants are transformed into products, while products can also revert back into reactants. This ongoing process continues until equilibrium is attained. It is important to note that equilibrium does not imply that the reaction has ceased; rather, it indicates that the rates of the forward and reverse reactions are balanced. Consequently, the concentrations of both reactants and products remain constant over time.

Understanding the concept of equilibrium can be somewhat challenging, as it does not refer to the quantities of reactants and products being equal. Instead, it pertains to the equality of the rates of the forward and reverse reactions. To illustrate this, consider a busy motorway where vehicles are traveling in both directions. If the number of cars entering the motorway equals the number of cars exiting, the motorway is said to be in a state of equilibrium. This analogy applies similarly to reversible reactions.

The position of equilibrium can be affected by changes in temperature, pressure, or concentration. For instance, increasing the temperature will shift the position of equilibrium to favor the endothermic reaction (the reaction that absorbs heat). This occurs because the system attempts to counteract the change by absorbing more heat, thereby reducing the overall temperature. Similarly, if the pressure is increased, the equilibrium will shift to favor the reaction that produces fewer gas molecules, as this adjustment helps to alleviate the pressure.

In summary, a reversible reaction reaches equilibrium when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. This equilibrium state can be influenced by variations in temperature, pressure, or concentration.