What does the symbol ⇌ mean in a chemical equation?

• A. Reversible reaction
• B. An irreversible reaction
• C. A catalyst is present
• D. Heat is absorbed

Answer: (A)

The symbol shows a reversible reaction. It means the process can go from left to right to form products, and from right to left to regenerate the reactants. When conditions allow, both directions occur at the same time and, at equilibrium, the forward and backward rates become equal so the amounts of reactants and products stay constant even though reactions are still happening. This is different from a single-arrow, irreversible reaction which proceeds in only one direction under the given conditions. A catalyst speeds up both directions but doesn’t change whether the reaction is reversible. The symbol itself doesn’t tell you about heat being absorbed or released.