Q. What type of reaction is the following reaction H2CO3 → H2O CO2

The reaction H2CO3 → H2O + CO2 is classified as a decomposition reaction, where carbonic acid breaks down into water and carbon dioxide. This is a thermal decomposition that occurs readily at room temperature because carbonic acid is unstable—it exists only briefly in aqueous solution before spontaneously decomposing into its constituent components. The reaction follows the classic decomposition pattern where one compound (AB) breaks apart into two or more simpler substances (A + B).

This particular decomposition reaction is important in biological and environmental chemistry. It occurs in your bloodstream as part of the carbon dioxide transport system: CO2 from cellular respiration combines with water in red blood cells to temporarily form carbonic acid (facilitated by the enzyme carbonic anhydrase), which then breaks down in the lungs to release CO2 for exhalation. The same reaction occurs when you open a carbonated beverage—the dissolved carbonic acid rapidly decomposes, releasing CO2 gas as bubbles. The reaction is essentially instantaneous and requires no external energy input, making it unusual compared to many decomposition reactions that require heating. Understanding this as a decomposition reaction helps explain why carbonated drinks go flat (the carbonic acid decomposes and CO2 escapes), why CO2 is exhaled from lungs rather than carbonic acid, and why carbonic acid cannot be isolated as a pure substance—it's simply too unstable and decomposes immediately.