# Preparation of sulfuric acid through Contact process

In the preparation of $\ce{H2SO4}$ through the Contact process, $\ce{H2SO4}$ is added to hot sulfur trioxide to form oleum. This oleum is then diluted by adding water to form $\ce{H2SO4}$.

$$\ce{H2SO4(l) + SO3(g) → H2S2O7(l)}$$

$$\ce{H2S2O7(l) + H2O(l) → 2 H2SO4(l)}$$

In a preparatory reaction, different reagents are used to obtain the desired product but here the product is itself a reactant and is used to make the product. Indirectly, $\ce{H2SO4}$ is being used to make $\ce{H2SO4}$.

Would this process be called as a preparation process?