Silicon tetrachloride (##SiCl_4##) can be prepared by heating ##Si## in chlorine gas: ##Si (s) + 2Cl_2(g) -> SiCl_4(l)##. In one reaction, 0.507 mole of ##SiCl_4## is produced. How many moles of molecular chlorine were used in the reaction?

demands at least ##1.14## ##mol## of ##Cl_2## gas.

The stoichiometric equation, which you have correctly written, clearly and explicitly shows that ##1## ##mol## of silicon (approx. ##28*g##) reacts with ##2*"moles"## of chlorine gas (approx. ##71*g##) to give ##1## ##mol## of ##SiCl_4##.

The equation establishes both the molar and mass balance.