Molarity Question from Lecture 10/5

[Lung Sheng Liang 3J]

I can't wrap my head around this.

Reactants -> Products
2Na(s) + 2H2O(I) -> 2NaOH(aq)+H2(g)
2mol + 2mol -> 2mol + 1mol

I don't understand why the number of moles doesn't match on both sides. I thought number of moles never change in reactions?

Sorry if this is too dumb of a question.

[Ryan_Kien_1L]

The moles of each individual element must remain constant for both sides of the reaction, the total number of moles of molecules can change.

[Helena Xu 1I]

A balanced reaction would have the same number of moles for each element on both sides. The stoichiometric coefficients on both sides wouldn't necessarily have to match.

[Crystal Pan 2G]

The moles at the bottom are describing the stoichiometric coefficients. As you can see in the reactants, there are 4 mol of H as 2mol of H20 = 2mol H2 which is 4 mol of H. And then at the right hand side, there are 2 mol of NaOH and H2, which means that there are 2 mol of H in the NaOH and 2 mol H in H2. The equation is balanced, but the stoichiometric coefficients at the bottom are different due to the hydrogen becoming H2 gas(hydrogen is a diatomic element)

[AndrewNguyen_2H]

The moles of each ELEMENT must remain the same on both sides, not the actual molecules themselves. For example, there are 4 Hydrogen moles on each side & there are 2 Oxygen on each side. The atoms just rearrange themselves.

[Siwa Hwang 3G]

If you multiply the coefficient by the subscript of the element, you can see that the number of moles on the reactant side equals to the number of moles on the product side.

For example, there are two H2 atoms on the left side which is 2 x 2 = 4 Hydrogen atoms. And 2 Hydrogen atoms from NaoH ( 2 x 1 = 2 ) and 1 H2 atom ( 1 x 2 = 2 ) which adds up to total of 4 Hydrogen atoms on the product side. Therefore, the number of atoms stays consistent throughout the reaction.

Hope this helped.