reactant

/riˈæktənt/ 0
a substance that participates in a chemical reaction, esp a substance that is present at the start of the reaction 反应物

noun [物质名词][化学] 反应物;反应剂

And that's on the reactant side.
反应物这一边。

单词造句:
网友用“Reactant”造句精选
Two moles reactant... What happens if I change the pressure? 两摩尔反应物。,如果我改变压强会怎么样?
If I have a beaker with some solid reactant on the bottom here. 如果在烧杯地步,有一些固态反应物。