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which statement is true regarding a chemical reaction?

even if the total number of atoms does not change, mass may not be conserved in the reaction
the total number of atoms changes, so mass is conserved in the reaction.
the total number of atoms does not change, so mass is conserved in the reaction.
even if the total number of atoms changes, mass may not be conserved in the reaction.

3 answers

The true statement regarding a chemical reaction is:

the total number of atoms does not change, so mass is conserved in the reaction.

This aligns with the Law of Conservation of Mass, which states that in a chemical reaction, the total mass of the reactants equals the total mass of the products, meaning mass is conserved. The number of atoms for each element is also conserved during the reaction.

FeCl3 + 3H2O -> Fe(OH)3 + 2HCl

iron chloride and water react according to the equation shown. what is the total mass of the reactants?

To calculate the total mass of the reactants in the given chemical equation:

\[ \text{FeCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{Fe(OH)}_3 + 3\text{HCl} \]

we first need to find the molar masses of the reactants:

  1. Molar mass of FeCl₃ (iron(III) chloride):

    • Fe: 55.85 g/mol
    • Cl: 35.45 g/mol
    • Molar mass of FeCl₃ = 55.85 g/mol (Fe) + 3 × 35.45 g/mol (Cl) = 55.85 + 106.35 = 162.20 g/mol

  2. Molar mass of H₂O (water):

    • H: 1.01 g/mol
    • O: 16.00 g/mol
    • Molar mass of H₂O = 2 × 1.01 g/mol (H) + 16.00 g/mol (O) = 2.02 + 16.00 = 18.02 g/mol

Now, we have 3 moles of H₂O in the reaction, so we calculate the total mass of water:

  • Total mass of 3H₂O = 3 × 18.02 g/mol = 54.06 g/mol

Now we can find the total mass of the reactants:

\[ \text{Total mass of reactants} = \text{Mass of FeCl}_3 + \text{Mass of 3H}_2\text{O} = 162.20 , \text{g/mol (FeCl}_3) + 54.06 , \text{g/mol (3H}_2\text{O)} = 216.26 , \text{g/mol} \]

Therefore, the total mass of the reactants is 216.26 g/mol. Note that this value is expressed per mole of the reactants; for actual calculations, you would multiply by the number of moles you are using in the reaction.