To determine the volume of CH4 (methane) required to react completely with 10 g of H2 (hydrogen), we need to first determine the molar ratio between the two reactants according to the balanced chemical equation for the reaction:

2H2 + CH4 -> 4HCl

From the balanced equation, we can see that 2 moles of H2 react with 1 mole of CH4.

First, calculate the number of moles of H2 in 10 g:

Molar mass of H2 = 2 g/mol
Number of moles of H2 = 10 g / 2 g/mol = 5 moles

Since the molar ratio between H2 and CH4 is 2:1, we can determine that 5 moles of H2 will react with 2.5 moles of CH4.

Next, we'll calculate the volume of CH4 at STP (standard temperature and pressure) using the ideal gas law:

PV = nRT

Where:
P = pressure (1 atm)
V = volume
n = number of moles
R = ideal gas constant (0.0821 L·atm/mol·K)
T = temperature (273 K)

In this case, the volume can be calculated using the equation:

V = nRT / P

V = 2.5 mol x 0.0821 L·atm/mol·K x 273 K / 1 atm
V = 56.6675 L

Therefore, the volume of CH4 required to react completely with 10 g of H2 is approximately 56.67 liters at standard temperature and pressure.