According to the chemical equation

2C₂H_6(g) + 7O_2(g) ---> 4CO_2(s) + 6H₂O_(g)

c) how many mol of ethane, assuming excess dioxygen, are required to form 3.7 mol of water?

Answer

The approach is nearly identical to that used in part a). We must use the stoichiometric ratio between water and ethane to answer the question. This ratio is obtained from the balanced chemical equation. According to the balanced chemical equation six mol of water are formed when two mol of ethane, C₂H₆, react. Water and ethane always combine in this ratio according to this equation. We can use this relationship as a unit conversion factor to convert between mol of water and mol of ethane.