C3 - Limiting Reactant

What is a balanced chemical equation used for?

To show the ratio in which reactants combine and products form.

What is a limiting reactant?

The reactant that is completely used up in a reaction, which stops the reaction.

What is an excess reactant?

The reactant that is not fully used up and remains after the reaction.

How does the limiting reactant affect the products?

The amount of product formed is directly proportional to the amount of limiting reactant.

If 1 mole of magnesium reacts with 1 mole of chlorine, how many moles of magnesium chloride are formed?

1 mole of magnesium chloride.

If 0.5 moles of magnesium react with 1 mole of chlorine, which is the limiting reactant?

Magnesium (because it is fully used up).

How many moles of magnesium chloride are made if 0.5 moles of magnesium react with 1 mole of chlorine?

0.5 moles.

0.5 moles of zinc react with 1 mole of iodine. Which is limiting?

Zinc is the limiting reactant.

How many moles of zinc iodide will be made from 0.5 moles of zinc and 1 mole of iodine?

0.5 moles.

How do you calculate the mass of a product from moles?

Mass = number of moles × relative formula mass (Mr).

Mr of zinc iodide = 319. If 0.5 moles form, what mass is produced? 0.5

319. If 0.5 moles form, what mass is produced? 0.5 × 319 = 159.5 g.

Example: 0.25 moles of HCl react with 0.25 moles of NaOH. Which is limiting?

Hydrochloric acid (HCl).

How many moles of sodium chloride will form from 0.25 moles of HCl and NaOH?

0.25 moles.

If 0.25 moles of NaCl form and Mr(NaCl) = 58.5, what is the mass produced?

58.5, what is the mass produced? = 0.25 × 58.5 = 14.6 g.

Example: 0.5 moles of copper sulfate react with 1 mole of magnesium. Which is limiting?

Copper sulfate.

How many moles of copper are produced from 0.5 moles of copper sulfate and 1 mole of magnesium?

0.5 moles.

If 0.5 moles of copper form and Ar(Cu) = 63.5,

what is the mass of copper produced? = 0.5 × 63.5 = 31.75 g.

When calculating product masses, which reactant should you always base your answer on? = The limiting reactant.

The limiting reactant.