How many o2 molecules are needed to react with 8.47 of s? Solution 2S + 3O2 --->

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Explanation / Answer

2S + 3O2 ---> 2SO3 First work out the moles of S that you have started with... Always use moles to calculate this kind of question. moles = mass / molar mass molar mass S = 32.07 g/mol moles S = 4.45 g / 32.07 g/mol = 0.1388 moles of S Now, the balanced equation tells you that 2 moles S needs 3 moles of O2 to fully react So 1 mole S needs 3/2 moles of O2 So moles O2 needed = 3/2 x moles S = 3/2 x 0.1388 moles = 0.2082 moles of O2 0.2082 moles of O2 are required to react with 4.45 g of S Every mole of any molecule has 6.022 x 10^23 molecules in it. This is called avagadros number and it is true for all molecules. So to find the number of molecukes of O2 in 0.2082 moles multiply by avagadros number. molecules of O2 = 0.2082 moles x 6.022 x 10^23 = 1.25 x 10^23 molecules of O2 (3 sig fig)

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