Chemical Reactions and Stoichiometry - SS1 Chemistry Past Questions and Answers - page 3

The balanced equation is: CH₄ + 2O₂ → CO₂ + 2H₂O

From the equation, we can see that for every one mole of methane (CH₄) combusted, one mole of carbon dioxide (CO₂) is produced.

Convert the given mass of methane (CH₄) to moles.

Number of moles of CH₄ = Mass / Molar mass

= 12 g / 16 g/mol = 0.75 mol

Determine the moles of carbon dioxide (CO₂) produced.

Since the molar ratio of CH₄ to CO₂ is 1:1, the number of moles of CO₂ produced is also 0.75 mol.

Convert the moles of CO₂ to grams.

Mass of CO₂ = Number of moles of CO₂ x Molar mass of CO₂

= 0.75 mol x 44 g/mol = 33 g

The molar mass of sodium hydroxide (NaOH) can be calculated by adding up the atomic masses of its constituent elements.

The atomic masses of sodium (Na), oxygen (O), and hydrogen (H) are as follows:

Sodium (Na) = 22.99 g/mol

Oxygen (O) = 16.00 g/mol

Hydrogen (H) = 1.01 g/mol

To calculate the molar mass of NaOH, we sum the atomic masses:

Molar mass of NaOH = Atomic mass of Na + Atomic mass of O + Atomic mass of H

= 22.99 g/mol + 16.00 g/mol + 1.01 g/mol

= 40 g/mol

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It allows us to determine the amounts of substances involved in a reaction, predict the yield of products, and understand the stoichiometric ratios between reactants and products.

The mole concept plays a fundamental role in stoichiometry. The mole is a unit used to measure the amount of a substance. One mole of any substance contains Avogadro's number (6.022 x 10²³) of particles, which could be atoms, molecules, ions, or other entities. The mole concept allows us to relate the mass of a substance to the number of moles, as well as the number of particles.

The importance of stoichiometry and the mole concept in chemical reactions can be illustrated through the following points:

1. Determining stoichiometric ratios: Balanced chemical equations provide the mole-to-mole ratios between reactants and products. These ratios allow us to determine the exact amount of one substance needed to react with another. By using stoichiometry, we can calculate the quantities of reactants required for a desired yield of products.
2. Predicting reaction outcomes: Stoichiometry enables us to predict the theoretical yield of products based on the amounts of reactants involved. The mole ratios in a balanced equation help us understand the maximum amount of product that can be obtained from a given amount of reactant. This information is crucial in industries where efficiency and product yield are important factors.
3. Limiting and excess reactants: Stoichiometry allows us to identify the limiting reactant in a chemical reaction. The limiting reactant is the reactant that is completely consumed, limiting the amount of product that can be formed. The concept of the mole helps us compare the amounts of reactants and determine which reactant will be exhausted first. This information is valuable in optimising reaction conditions and determining the actual yield of a reaction.
4. Molar mass calculations: The mole concept is utilised to calculate the molar mass of a substance, which is the mass of one mole of that substance. The molar mass is essential for converting between mass and moles, allowing us to perform stoichiometric calculations. It serves as a conversion factor in determining the number of moles from a given mass of a substance and vice versa.