Water can be decomposed by electrolysis into hydrogen gas and oxygen gas.What mass of water must decompose to fill a 3.00 L flask to a total pressure of 2.00 atm at 298 K with a mixture hydrogen and oxygen? (R = 0.08206 L⋅atm/mol⋅K) 2 H₂O( )→ 2 H₂(g)+ O₂(g)

Question

Quizplus · Accepted Answer

First, we need to calculate the number of moles of gas needed to fill the flask at the given conditions. We can use the ideal gas law for this:

PV = nRT

where P is the pressure (2.00 atm), V is the volume (3.00 L), n is the number of moles, R is the gas constant (0.08206 L⋅atm/mol⋅K), and T is the temperature (298 K).

Solving for moles:

n = PV/RT = (2.00 atm)(3.00 L)/(0.08206 L⋅atm/mol⋅K)(298 K)

n = 0.240 mol

According to the balanced chemical equation, 2 moles of water decompose to produce 2 moles of hydrogen gas and 1 mole of oxygen gas:

2 H2O(l) → 2 H2(g) + O2(g)

Therefore, we need half as many moles of water to produce the same amount of hydrogen and oxygen:

n(H2O) = 0.240 mol/2 = 0.120 mol

The molar mass of water is 18.015 g/mol, so the mass of water needed is:

m(H2O) = n(H2O) x M(H2O) = 0.120 mol x 18.015 g/mol = 2.162 g

Therefore, the best choice is B, 2.95 g, which is the closest option to 2.162 g.

Water Can Be Decomposed by Electrolysis into Hydrogen Gas and Oxygen