Question

At STP, which sample contains the same number of molecules as 3.0 liters of H2(g)?

A) 1.5 L of NH3(g)
B) 2.0 L of CO2(g)
C) 3.0 L of CH4(g)
D) 6.0 L of N2(g)

Answer 1

Answer is: C) 3.0 L of CH4(g).

Vm = 22.4 L/mol; molar volume at STP (Standard Temperature and Pressure).

At STP one mole of gas occupies 22.4 liters of volume.

In this question all substances are gases, amount of substance depends on volume of the gas.

Same volume, same number of molecules.

So 3 liters of hydrogen gas (H₂) has the same number of molecules as 3 liters of methane gas (CH₄).