Find the formula weight of the reactant if the formula weight of the product is $54 \ u$ and the percent atom economy is $75$. (in $u$)

According to the reaction,$Mg_{(s)} + 2HCl_{(aq)} \longrightarrow MgCl_{2_{(aq)}} + H_{2_{(g)}} \uparrow$,calculate the mass of $Mg$ required to liberate $4.48 \ dm^3$ of $H_2$ gas at $STP$. (Molar mass of $Mg = 24 \ g \ mol^{-1}$) (in $g$)

Based on the equation $C_6H_{6(l)} + \frac{15}{2} O_{2(g)} \rightarrow 6CO_{2(g)} + 3H_2O_{(l)}$,the enthalpy change is $\Delta H = -3264.4 \, kJ \, mol^{-1}$. How much energy in $kJ$ is released when $7.8 \, g$ of benzene is burned in air?

The formula of a gaseous hydrocarbon which requires $6$ times of its own volume of $O_{2}$ for complete oxidation and produces $4$ times its own volume of $CO_{2}$ is $C_{x}H_{y}$. The value of $y$ is $......$ .

What is the normality of $1.5 \ M \ H_3PO_4$ (in $.5$)?

How many moles of methane are required to produce $22 \ g$ of $CO_2 \ (g)$ after combustion (in $mol$)?