3.01×10²³molecules.
The formula for the number of molecules of a compound given the number of moles is expressed as:
[tex]nu\text{mber of molecules=moles}\times6.02\times10^{23}[/tex]Get the moles of ethane gas using the formula:
[tex]\begin{gathered} \text{moles of ethane=}\frac{Mass\text{ of ethane}}{Molar\text{ mass of ethane}} \\ \text{Moles of ethane=}\frac{15}{2(12)+1(6)} \\ \text{Moles of ethane}=\frac{15}{30}\text{moles} \\ \text{Moles of ethane}=0.5\text{moles} \end{gathered}[/tex]Determine the required number of molecules of ethane
[tex]\begin{gathered} nu\text{mber of mol}ecules=0.5\times6.02\times10^{23} \\ nu\text{mber of mol}ecules=3.01\times10^{23} \end{gathered}[/tex]Hence the molecule of ethane gas that is in 15 grams of the compound is 3.01×10²³molecules.