Question

Sodium silicyde reacts with water to make hydrogen gas that can be used as a fuel. The reaction that accomplishes this has the balanced chemical equation: 2 NaSi(s) + 5H2O(l) → Na2Si2O5(s) + 5H2(g) Suppose a boat engine based on using hydrogen were devised using this reaction and sodium silicide is in a fuel tank (that reacts with water brought in from the body of water on which the boat operates). What happens to the mass of the fuel tank with time and operation of the engine? It ["increases", "", "stays the same", "decreases"] select one because ["the hydrogen product is a gas and leaves the system", "oxygen is added to the Na and Si (from the water)", "fuel is always consumed in an engine", "the density of a more complicated substance like Na2Si2O5 exceeds the more simply NaSi.", "two moles of sodium silicyde are consumed for every mole of solid product created"] select one .

Answer 1

What happens to the mass of the fuel tank with time and operation of the engine? Correct answer is : It increases because oxygen is added to the Na and Si (from the water).

Explanation

From the reaction equation, for each mole of NaSi, five moles of H₂O is added

mass of one mole H₂O = 18.0 g

mass of five moles H₂O = 5 * (18.0 g) = 90.0 g

For each moles of NaSi consumed, 5 moles H₂ is released

mass of one moles H₂ = 2.0 g

mass of five moles H₂ = 5 * (2.0 g) = 10.0 g

change in mass = mass of reactants - mass of products

change in mass = (90.0 g) - (10.0 g)

change in mass = 80.0 g

Since change is positive, therefore, mass of fuel tank increases.