Question

When is the system $A + B = C + D$ at equilibrium?
A.The forward reaction has stopped.
B.Both the forward and the reverse reactions have stopped.
C.The reverse reaction has stopped.
D.Neither the forward nor the reverse reaction has stopped.

Answer 1

Hint: A chemical reaction is a process that converts one or more substances, known as reactants, into one or more other substances, known as products. Substances may be classified as chemical elements or compounds. A chemical reaction transforms the constituent atoms of the reactants to produce various products.

Complete answer:
Chemical equilibrium is the condition of a chemical reaction in which all the reactants and products are present in quantities that have no further tendency to change over time, resulting in no detectable change in the system's properties.
Chemical equilibrium is the thermodynamic equilibrium in a system that allows for both forward and reverse chemical reactions. If the system achieves chemical equilibrium, the rates of both reactions proceeding in opposite directions are equal.
The forward and reverse reactions occur at the same rates in a chemical equilibrium, and the quantities of products and reactants remain stable.
Chemical equilibrium is a dynamic process in which the quantities of both the reactant and the product shift at the same rate.
So, the system $A + B = C + D$ is at equilibrium when neither the forward nor the reverse reaction has stopped.

Note:
It must be noted that the changes in concentration, temperature, and strain can all influence the equilibrium state of a reversible reaction. When a certain proportion of a mixture remains as reactants and the remainder leaves as products, the mixture is said to be in equilibrium.