You react 25.0 g hydrogen gas with 30.2 g oxygen gas. Determine the mass of water that can be produced from these reactants.

This is a limiting reagent problem? How do I know that? Because BOTH reactants are given. Basically what you do is to work TWO simple stoichiometry problems to determine the amount of water produced, then take the SMALLER value. Here is a solved example of a simple stoichiometry problem. Just follow the steps.

http://www.jiskha.com/science/chemistry/stoichiometry.html

To determine the mass of water produced, we need to use the concept of stoichiometry and balance the chemical equation for the reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O).

The balanced chemical equation is:
2H2 + O2 → 2H2O

First, we need to convert the mass of hydrogen gas (H2) and oxygen gas (O2) to moles. To do this, we divide the given masses by their respective molar masses.

The molar mass of hydrogen gas (H2) is 2.016 g/mol, and the molar mass of oxygen gas (O2) is 32.00 g/mol.

Number of moles of hydrogen gas:
moles H2 = mass H2 / molar mass H2
moles H2 = 25.0 g / 2.016 g/mol ≈ 12.4 mol

Number of moles of oxygen gas:
moles O2 = mass O2 / molar mass O2
moles O2 = 30.2 g / 32.00 g/mol ≈ 0.944 mol

According to the balanced chemical equation, the molar ratio of H2 to H2O is 2:2, and the molar ratio of O2 to H2O is 1:2.

Since we have excess oxygen gas, we will consider the limiting reactant to be hydrogen gas (H2), as it is completely consumed in the reaction. Therefore, the moles of water produced will be determined by the moles of hydrogen gas.

From the balanced equation, we know that 2 moles of H2 will produce 2 moles of H2O.

Therefore, moles of water produced:
moles H2O = moles H2

Now, we convert the moles of water to mass by multiplying it by the molar mass of water (H2O), which is 18.02 g/mol.

Mass of water produced:
mass H2O = moles H2O × molar mass H2O
mass H2O = 12.4 mol × 18.02 g/mol ≈ 223.2 g

Therefore, the mass of water that can be produced from the given reactants is approximately 223.2 grams.