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 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).

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.