1. Write the Balanced Chemical Equation:

The balanced chemical equation for the reaction is:

CS₂(g) + 4H₂(g) → CH₄(g) + 2H₂S(g)

2. Use the Mole Ratio:

The balanced equation tells us that 4 moles of H₂ are required to produce 1 mole of CH₄.

3. Apply Avogadro's Law:

At STP (Standard Temperature and Pressure), equal volumes of gases contain equal numbers of moles. Therefore, the mole ratio from the balanced equation can be directly applied to volumes.

4. Calculate the Volume of H₂:

* We know 2.50 L of CH₄ is produced.

* Using the mole ratio, 2.50 L of CH₄ requires 4 times that volume of H₂.

Therefore, we need 10.0 L of hydrogen gas to react with CS₂ to produce 2.50 L of CH₄ at STP.