Hydrogen reacts with oxygen as shown in the equation
2H2+O2~2H2O
In an experiment,100cm³of hydrogen gas was mixed with 100cm³ of oxygen gas and the mixture heated to form H2O.Which of the gases was in excess and by how much?
In the balanced equation, it is shown that 2 moles of hydrogen react with 1 mole of oxygen to form 2 moles of water. This means that the ratio of hydrogen to oxygen in the reaction is 2:1.
If 100 cm³ of hydrogen gas is mixed with 100 cm³ of oxygen gas, we can calculate the number of moles of each gas by using the ideal gas law, PV = nRT.
For hydrogen gas (H2):
PV = nRT
(1 atm) (100 cm³) = n (0.0821 L·atm/mol·K) (273 K)
n = 0.004 moles
For oxygen gas (O2):
PV = nRT
(1 atm) (100 cm³) = n (0.0821 L·atm/mol·K) (273 K)
n = 0.002 moles
From the calculations, we can see that there are 0.004 moles of hydrogen and 0.002 moles of oxygen in the mixture.
Since the ratio of hydrogen to oxygen in the reaction is 2:1, we would need 0.002 moles of oxygen to react with the 0.004 moles of hydrogen. However, we have 0.002 moles of oxygen in the mixture, so it is the limiting reactant.
Therefore, oxygen gas is in excess by 0.002 moles.