how many moles of oxygen are required for the combustion of 25.5 g of magnesium

write the balanced equation:

2Mg+O2>>2MgO So according to the equation, figure the moles of Mg (25.5/atomicmassMg), then half that is required number of moles of O2.

Here is a step by step example of how to work stoichiometry problems.

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

To determine the number of moles of oxygen required for the combustion of magnesium, we need to use the balanced chemical equation for the combustion of magnesium. The balanced equation is:

2 Mg + O2 → 2 MgO

From the balanced equation, we can see that it takes 1 mole of oxygen for every 2 moles of magnesium that react.

First, we need to calculate the number of moles of magnesium in 25.5 g. The molar mass of magnesium (Mg) is approximately 24.31 g/mol.

Number of moles of magnesium = Mass of magnesium / Molar mass of magnesium
= 25.5 g / 24.31 g/mol
= 1.05 mol

Since the ratio of magnesium to oxygen in the balanced equation is 2:1, we can say that 1.05 moles of magnesium requires half as many moles of oxygen, or 0.525 moles.