Stoichiometry

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Use the following reaction to determine the number of liters of hydrogen that must react with 20 L of oxygen to form water vapor.

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Equation:

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2H2 + O2 - > 2H2O

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Stoichiometry is the ratio of reactants to products in a balanced chemical reaction equation.

the stoichiometry in this case of H₂ to O₂ is 2:1.

This means that 2 moles of H₂ reacts with 1 mol of O₂.

we have been asked to calculate the volume of H₂ gas.

Since both O₂ and H₂ are gases, at standard conditions its stated that molar volume of gases is 22.4 L

This means that at standard temperature and pressure, 1 mol of any gas occupies a volume of 22.4 L

first we need to calculate the number of O₂ moles reacted;

22.4 L of gas - 1 mol of O₂

1 L of gas - 1/22.4 mol/L

then 20 L of O₂ - 1/22.4 mol/L * 20 L = 0.89 mol

stoichiometry of H₂ to O₂ is 2:1

the number of H₂ moles = 0.89*2 = 1.79 mol

1 mol occupies 22.4 L

Therefore 1.79 mol = 22.4 L/mol * 1.79 mol = 40 L

Therefore it can be seen that stoichiometry applies to volumes as well.

volume of H₂ : O₂ = 40 L : 20 L = 2:1

volume and moles both can be determined by stoichiometry.

Volume of H₂ reacted = 40 L