Question

how much h2 is required to react with 12.7 grams of n2 to form 15.4 grams of nh3?

reaction	reactant(s)	product(s)
mass	12.7 g	?	15.4 g

Explanation:

Step1: Apply the law of conservation of mass

The law of conservation of mass states that the total mass of reactants equals the total mass of products in a chemical reaction. Let the mass of $H_2$ be $x$.
$12.7 + x=15.4$

Step2: Solve for $x$

Subtract 12.7 from both sides of the equation.
$x = 15.4 - 12.7$
$x=2.7$

Answer:

2.7 g