Problem #20: Stoichiometry [Solved]

Daniel Iyamuremye -

  1. There is a chapter or area in Chemistry called “Stoichiometry”. Explain what it is about.

  2. A gas cylinder contains 1,000 g of methane gas.

    a. Write a balanced chemical equation for the combustion of methane, knowing that methane burns in oxygen to give carbon dioxide and water.

    b. How many grams and moles of oxygen do you need to completely burn that quantity of methane?

    c. How many grams and moles of carbon dioxide will be produced?

    d. How many grams and moles of water will be produced?

Solution:

  1. Stoichiometry is a branch of Chemistry that deals with the calculation of the relative proportions or relative quantities in which elements form compounds or in which substances react in a given chemical reaction. Stoichiometry is important, not only in theoretical study of Chemistry, but also in experimental and chemical industrial production.
Attention: Any stoichiometric calculation must start by establishing a “balanced equation of the chemical reaction”, otherwise the calculation is doomed to fail.
  1. Let’s consider the chemical reaction:
    CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
    1 mole CH4 + 2 moles O2 → 1 mole CO2 + 2 moles H2O

a. Calculation of the quantity of oxygen needed:

According to the chemical equation, 1 mole of CH4 reacts with 2 moles of O2, in other words 16 g of CH4 reacts with 64 g of O2.
Then 1,000 g (62.5 moles) of CH4 will react with: (64 x 1000)/16 = 4,000 g of O2 (125 moles of O2)

b. Calculation of the quantity of CO2 produced:

According to the chemical equation, 1 mole of CH4 produces 1 mole of CO2, or 16 g of CH4 produce 44 g of CO2
Then 1,000 g (62.5 moles) of CH4 will produce: (44 x 1,000)/16 = 2,750 g of CO2 (62.5 moles of CO2).

c. Calculation of the quantity of H2O produced:

According to the chemical equation, 1 mole of CH4 produces 2 moles of H2O, or 16 g of CH4 produce 36 g of H2O
Then 1,000 g (62.5 moles) of CH4 will produce: (36 x 1,000)/16 = 2,250 g of H2O (125 moles of H2O).

d. Checking if the law of mass conservation is fulfilled:

  • Reactants: 1,000 g + 4,000 g = 5,000 g
  • Products: 2,750 g + 2,250 g = 5,000 g

The law is fulfilled.

The role and importance of Stoichiometry in Chemistry

Stoichiometry is very important and fundamental:

  1. In the study of chemistry: it is through stoichiometric calculations that problems related to quantities of reactants and products can be solved. It is also the stoichiometry of the reactions that allows to prepare and set up different experiments.
  2. In industrial chemistry: stoichiometric calculations are important in industrial production processes such as, determination of the quantities of reactants involved in a process, and determination of the quantities of products expected.