12.0g of Zinc reacts with 20.0g of Iron III Chloride. What is the limiting reactant?

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The balanced chemical reaction between zinc and iron III chloride can be written as this:

3Zn + 2FeCl3 -> 3ZnCl2 + 2Fe

Here, 3 moles of zinc reacts with 2 moles of iron III chloride to produce 3 moles of zinc chloride and 2 moles of iron (III). This is...

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The balanced chemical reaction between zinc and iron III chloride can be written as this:

3Zn + 2FeCl3 -> 3ZnCl2 + 2Fe

Here, 3 moles of zinc reacts with 2 moles of iron III chloride to produce 3 moles of zinc chloride and 2 moles of iron (III). This is a single replacement reaction where zinc replaces iron.

We are given with 12 g of zinc and 20 g of iron III chloride. First, we need to determine the moles of each species and then figure out which one is limiting as per the balanced chemical equation.

Zinc has an atomic mass of 65.38 g/moles. 12 g of zinc will contain 12/65.38 = 0.184 moles of zinc.

Iron III chloride has a molecular mass of 162.2 g/mol. 20 g of iron III chloride will contain 20/162.2 moles = 0.123 moles of iron III chloride.

Using the balanced chemical equation mentioned above, 3 moles of zinc reacts with 2 moles of iron III chloride, and hence 0.184 moles of zinc (or 12 g of zinc) will react with 2/3 x 0.184 moles = 0.123 moles of iron III chloride.

This is the number of moles of iron III chloride that is available in 20 g of iron III chloride.

Hence, there is no limiting reactant: both the reactants are provided in just the right amounts. The limiting substance is the one that is present in less than sufficient amount and hence controls the reaction and the amount of reactants used and products generated.

Hope this helps.

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