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Use the chemical equation to complete the activity.

4Fe + 3O2 → 2Fe2O3
Write the chemical equation in sentence form.
A scientist adds 15.4 grams of Fe to 3.6 grams of O2 to start the reaction. What should be the mass of the products?
Does this equation demonstrate the Law of Conservation of Matter? Explain specifically how you know.

1 answer

Chemical Equation in Sentence Form

The reaction can be expressed in sentence form as follows: "Four atoms of iron react with three molecules of oxygen to produce two formula units of iron(III) oxide."

Mass of the Products

To determine the mass of the products, we first need to find the mass of the reactants:

  1. Calculate the molar mass of the reactants:

    • Molar mass of Iron (Fe) = 55.85 g/mol
    • Molar mass of Oxygen (O2) = 32.00 g/mol

  2. Calculate the moles of each reactant:

    • Moles of Fe: \[ \text{Moles of Fe} = \frac{15.4 \text{ g}}{55.85 \text{ g/mol}} \approx 0.276 \text{ mol} \]
    • Moles of O2: \[ \text{Moles of O2} = \frac{3.6 \text{ g}}{32.00 \text{ g/mol}} \approx 0.113 \text{ mol} \]

  3. Using the stoichiometry of the balanced equation:

    • According to the reaction, 4 moles of Fe react with 3 moles of O2.
    • The ratio of Fe to O2 is \( \frac{4 \text{ Fe}}{3 \text{ O2}} \).

  4. Determine the limiting reactant:

    • To find how many moles of Fe are needed for the available O2: \[ \text{Moles of Fe required} = 0.113 \text{ mol O2} \times \frac{4 \text{ mol Fe}}{3 \text{ mol O2}} = 0.151 \text{ mol Fe} \]
    • Since we have 0.276 mol of Fe available and only need 0.151 mol, O2 is the limiting reactant.

  5. Calculate the products formed:

    • The balanced reaction shows that 3 moles of O2 produce 2 moles of Fe2O3.
    • From the moles of O2 available: \[ \text{Moles of Fe2O3 produced} = 0.113 \text{ mol O2} \times \frac{2 \text{ mol Fe2O3}}{3 \text{ mol O2}} \approx 0.0753 \text{ mol Fe2O3} \]

  6. Calculate the mass of Fe2O3 produced:

    • Molar mass of Fe2O3 = (2×55.85) + (3×16.00) = 159.7 g/mol
    • Mass of Fe2O3: \[ \text{Mass of Fe2O3} = 0.0753 \text{ mol} \times 159.7 \text{ g/mol} \approx 12.03 \text{ g} \]

  7. Total mass of products:

    • Since the products are Fe2O3 and no other products are formed or lost, the total mass of products will consist solely of the Fe2O3 formed.

Does this equation demonstrate the Law of Conservation of Matter?

Yes, this equation demonstrates the Law of Conservation of Matter. The law states that matter cannot be created or destroyed in a chemical reaction; it can only change forms.

In our scenario:

  • The total mass of the reactants (15.4 g of Fe + 3.6 g of O2 = 19.0 g) is equal to the total mass of the product formed (approximately 12.03 g of Fe2O3), which might suggest a discrepancy if not accounted correctly for any unreacted materials. However, if we consider only the amounts as per the limiting reactant, we still find that the mass of reactants that participated is conserved.
  • The number of atoms of each element on the reactant side is equal to the number of atoms on the product side. There are four Fe atoms and six O atoms in total on both sides, confirming that the atoms are simply rearranged and there is no net loss or gain of matter.

Therefore, the equation adheres to the Law of Conservation of Matter.