Practice Questions

The coefficients in a balanced chemical equation represent the relative numbers of molecules or moles participating in the reaction. Masses depend on molar masses and are not directly represented by the coefficients. Concept tested: Significance of mole ratios in stoichiometry.

The balanced equation shows that 1 mole of Ca reacts with 2 moles of HCl. Therefore, 3 moles of Ca require 6 moles of HCl. Concept tested: Mole ratio application.

The limiting reagent is the reactant that is consumed first and determines the maximum amount of product formed. It is not necessarily the reactant with the smallest mass or highest molar mass. Concept tested: Limiting reagent concept.

The molar mass of CO₂ is 44 g mol⁻¹. Therefore, 44 g corresponds to exactly one mole. Concept tested: Mass-to-mole conversion.

One mole contains 6.02 × 10²³ molecules. Therefore, 0.25 mole contains one-fourth of this value, equal to 1.51 × 10²³ molecules. Concept tested: Representative particles.

The equation shows that 2 moles of K produce 1 mole of H₂. Therefore, 8 moles of K produce 4 moles of hydrogen gas. Concept tested: Stoichiometric mole ratio.

At STP, one mole of gas occupies 22.4 L. Therefore, 89.6 ÷ 22.4 = 4 moles. Concept tested: Gas volume to mole conversion.

According to the balanced equation, 2 moles of HgO produce 1 mole of O₂. Therefore, 8 moles of HgO produce 4 moles of O₂. Concept tested: Stoichiometric calculations.

Three moles contain 3 × 6.02 × 10²³ = 1.81 × 10²⁴ molecules. The other values represent fewer moles. Concept tested: Mole-to-particles conversion.

The balanced equation shows that 3 moles of Cl₂ produce 2 moles of AlCl₃. Therefore, 6 moles of Cl₂ produce 4 moles of AlCl₃. Concept tested: Mole ratio from a balanced equation.