Question

1. How many moles of sodium will react with water to produce 4.0 mol of
hydrogen in the following reaction?
2Na(s) + 2H2O(1) ► 2NaOH(aq) + H2(g) ans: 8.0 mol Na

Answer 1

Answer:

Explanation:

The equation tells you that for every mol of H2 you need 2 mols of Na to get it.

1 H2   /  4 mols H2  = 2  mols Na  /   x    Cross multiply

1*x = 4 * 2

x = 8 mol Na

Answer 2

Answer:

8 moles of sodium will react with water to produce 4.0 mol of  hydrogen in the reaction.

Explanation:

The rule of three or is a way of solving problems of proportionality between three known values and an unknown value, establishing a relationship of proportionality between all of them. That is, what is intended with it is to find the fourth term of a proportion knowing the other three. Remember that proportionality is a constant relationship or ratio between different magnitudes.

If the relationship between the magnitudes is direct, that is, when one magnitude increases, so does the other (or when one magnitude decreases, so does the other), the direct rule of three must be applied. To solve a direct rule of three, the following formula must be followed:

a ⇒ b

c ⇒ x

Then

$x=\frac{c*b}{a}$

In this case you can see that by stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction), they react and obtain:

• 2 moles of sodium (Na)
• 2 moles of water (H₂O)
• 2 moles  sodium hydrogen (NaOH)
• 1 mole of hydroxide H₂

But in this case 4 moles of hydrogen are produced. Then the rule of three applies as follows: If by stoichiometry 2 moles of sodium produce 1 mole of hydrogen, how many moles of sodium are needed to produce 4 moles of hydrogen?

$moles of sodium=\frac{4molesofhydrogen*2molesofsodium}{1mole of hydrogen}$

moles of sodium=8

Then, 8 moles of sodium will react with water to produce 4.0 mol of  hydrogen in the reaction.