A 12. 2 g sample of X reacts with a sample of Y to form 78.9 g of XY. What is the mass of Y that reacted?

Jan 26, 2017

$\text{Mass}$ $=$ 78.0*g-12.2*g=?

Explanation:

All chemical reactions CONSERVE mass. What does this mean?

It means that if I start with $10 \cdot g$ of reactants, from all source, AT MOST I can get $10 \cdot g$ of product.

$\text{Garbage in equals Garbage out!}$

Here I finished with a $78.9 \cdot g$ mass of $X Y$. There were $12.2 \cdot g$ of $X$. And the balance must represent the mass of $Y$.