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Reaction masses

Reacting masses

In all chemical reactions:

reactants → products

The greater the amount of reactants used, the greater the amount of products produced.

The total mass of reactants used is equal to the total mass of the products made.

For any one reaction, the ratio of reactant to product does not change. So if the ratio of mass of reactants to mass of products is known, the mass produced by any mass of reactant can be calculated:

How to calculate reactant mass

  1. Work out the ratio of reactant to product (or product to reactant) for the required situation. (You want the unknown on the top!)
  2. Work out the ratio of reactant to product (or product to reactant) from the masses given.
  3. Write them equal to each other.
  4. Rearrange the equation.
  5. Work out the answer.
Question
When 12g of carbon is burned in air, 44g of carbon dioxide is produced. How much carbon is needed to produce 11g of carbon dioxide?
Answer
  1. carbon / carbon dioxide = χ / 11
  2. carbon / carbon dioxide = 12 / 44
  3. χ / 11 = 12 / 44
  4. χ = (12 x 11) / 44
  5. χ = 3g

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