Question

6CO2 + 6H2O ---> C6H12O6 + 6O2 (photosynthesis)

1. What will be the limiting reagent if the plant uses 88g of carbon dioxide and 54g of water?

2. What is the excess reagent?

Answer 1

Ans. Moles of CO2 in 88 gm = weight of CO₂ / molecular weight of CO₂

= 88 gm / 44gm per mol

= 2 moles CO₂

Moles of H₂O = 54 gm / 18 gm per mol = 3 moles.

Since, equal number of moles of CO₂ and H₂O are required for the synthesis of glucose;

And, moles of H₂O (3 moles) > moles of CO₂

Ans. 1. CO₂ is the limiting reagent as being the least (2 moles CO₂ compared to 3 moles of H₂O) in the equimolar stoichiometric reaction.

Ans. 2. Water is the excess reagent. As 1 mol of H₂O still remains unused after CO₂ is completely consumed up during photosynthesis.