a) why should you use moles in stoichimetric problems?

b) solid reacts violently with water, producing heat, hydrogen gas, and sodium hydroxide. how many molecules of hydrogen gas are formed when 48.7 g of soodium are added to water?
2Na + 2H2P ------> 2NaOH + H2

a)because reactions occur by mols.

b) You have the equation.
Convert g Na to mols.
Convert mols Na to mols H2 gas using the coefficients in the balanced equation.
Convert mol H2 to molecules remembering that 1 mol of a gas contains 6.02 x 10^23 molecules. Post your work if you need addition help.

i still don't get what to do for b

John--I have worked several of these problems for you over the last 2-3 weeks. You need to learn to do these. I gave you instructions in my first response. Tell me what it is about the first step; i.e., convert g Na to mols Na.

a) Mole is a unit of measurement in chemistry that helps us quantify the amount of a substance in a chemical reaction. It allows us to calculate the reactants and products' quantities accurately and determine the ratios in which they combine or are produced. Using moles in stoichiometric problems provides a standardized approach to solve chemical equations and perform calculations based on the law of conservation of mass.

b) To determine the number of molecules of hydrogen gas formed when 48.7 g of sodium reacts with water, we need to follow a step-by-step process:

1. Convert the given mass of sodium (48.7 g) to moles by using its molar mass. The molar mass of sodium is 22.99 g/mol.

Moles of sodium = mass of sodium / molar mass of sodium
= 48.7 g / 22.99 g/mol
= 2.12 mol (rounded to two decimal places)

2. Based on the balanced chemical equation, we can see that 2 moles of sodium react to produce 1 mole of hydrogen gas.

3. Using the stoichiometric ratio, we can calculate the moles of hydrogen gas produced:

Moles of hydrogen gas = Moles of sodium x (1 mole of H2 / 2 moles of Na)
= 2.12 mol x (1/2)
= 1.06 mol

4. Finally, we can convert the moles of hydrogen gas to molecules by using Avogadro's number, which states that 1 mole of any substance contains 6.022 x 10^23 particles (molecules in this case).

Number of molecules of hydrogen gas = Moles of hydrogen gas x Avogadro's number
= 1.06 mol x (6.022 x 10^23 molecules/mol)
= 6.38 x 10^23 molecules

Therefore, when 48.7 g of sodium is added to water, approximately 6.38 x 10^23 molecules of hydrogen gas are formed.