Question

In the solar fuel cell experiment, the fuel cell was used to run the fan. It is mentioned that approximately 9.0 mL of H2 gas was used to run the fan.

a. If the pressure of the gas is 1.00 atm at 25°C, how many moles of H2 gas were used? Write the answer in scientific notation with two significant figures. For example, if the answer is 0.004463, it should be entered as 4.5E-3. NO UNITS in the answer. Fill in the blank.

b. Using the answer in part a, how many moles of O2 gas were used to power the fan? Write the answer in scientific notation with two significant figures. For example, if the answer is 0.004463, it should be entered as 4.5E-3. NO UNITS in the answer. Fill in the blank.

Answer 1

Using the ideal gas law, we find that approximately 3.7E-4 moles of H2 gas were used to run the fan. From the balanced equation for the reaction of hydrogen and oxygen, we can determine that 1.8E-4 moles of O2 were used since it takes 2 moles of H2 to react with 1 mole of O2.

Step-by-step explanation:

To answer the question about the number of moles of H2 gas used, we will use the ideal gas law PV = nRT. The given conditions are a volume of 9.0 mL or 0.009 L, a pressure of 1.00 atm, and a temperature of 25°C which is 298.15 K (25 + 273.15). The universal gas constant R is 0.0821 L atm/(mol K). Now we can plug in the values:

PV = nRT

(1.00 atm)(0.009 L) = n(0.0821 L atm/(mol K))(298.15 K)

n ≈ 3.7E-4 moles

Since the balanced chemical equation is:

2 H2(g) + O2(g) → 2 H2O(g)

It shows that 2 moles of H2 reacts with 1 mole of O2, which means the number of moles of O2 is half the number of moles of H2:

3.7E-4 moles H2 / 2 ≈ 1.8E-4 moles O2