A student carefully placed 15.6 g of sodium in a reactor supplied with excess quantity of chlorine gas. When the reaction was complete, the student obtained 39.7 g of sodium chloride. How many grams of chlorine gas reacted? How many grams of sodium reacted?
The balanced chemical equation for this reaction can be written as:
2 Na + Cl2 -> 2 NaCl
That is, 2 moles of sodium reacts with 1 mole of chlorine gas to generate 2 moles of sodium chloride. The atomic mass of sodium is 23 gm/mole, chlorine is 35.5 gm/mole and hence that of sodium chloride is 58.5 gm/mole.
39.7 gm of sodium chloride was obtained, or
39.7/58.5 mole = 0.68 moles of sodium chloride was obtained.
Amount of sodium available = 15.6 gm = 15.6/23 = 0.68 moles.
Since 2 moles sodium generate 2 moles sodium chloride, or 1 mole sodium will generate 1 mile sodium chloride and hence 0.68 moles of sodium will generate 0.68 mole sodium chloride, which is what we got. Hence all the sodium, 15.6 gm, reacted.
2 moles sodium reacts with 1 mole chlorine gas, or 0.68 moles will react with 0.34 moles of gas, which is same as 0.34 × 71 gm = 24.1 gm chlorine gas.
Hope this helps.