Question

(pls help!) What mass of oxygen atoms is required to react completely with 30 u of hydrogen atoms?​

Answer 1

• 2H_2+O_2—»2H_2O

One mole Hydrogen need 1/2mol O_2 .

Moles of Hydrogen

• 30u/1u
• 30mol

Moles of O_2

• 30/2
• 15mol

Answer 2

$\qquad\qquad\huge\underline{{\sf Answer}}$

Let's get to the reaction first ~

$\qquad \qquad \rm 2H_2 + O_2 \rightarrow 2H_2O$

Here, we can infer that if we need 1 mole oxygen gas to react with 2 moles Hydrogen gas.

So, the number of Oxygen gas molecules we need to react should be half the number of Hydrogen gas molecules.

Number of Hydrogen gas molecules is :

$\qquad \sf  \dashrightarrow \: \dfrac{30}{2}$

$\qquad \sf  \dashrightarrow \: 15$

Number of Oxygen gas molecules needed is :

$\qquad \sf  \dashrightarrow \: \dfrac{15}{2}$

Number of Oxygen atoms needed :

$\qquad \sf  \dashrightarrow \: \dfrac{15}{2} \times 2$

$\qquad \sf  \dashrightarrow \: {15} \: atoms$

One atom of Oxygen weight 16 u, so 15 atoms weight ~

$\qquad \sf  \dashrightarrow \: {15} \times 16$

$\qquad \sf  \dashrightarrow \: 240 \: u$

So, we need 240 u of Oxygen atoms to react completely with 30 u of Hydrogen atoms.