化学老师解释了如何利用化学计量学计算反应中所需的氧气量。

The chemistry teacher explained how to use ___stoichiometry to calculate the amount of oxygen needed in the reaction.

化学课上，我们学习了如何用化学计量学计算反应物的比例。

In chemistry class, we learned how to use ___stoichiometry to calculate reactant ratios.