Answer to Question #173159 in Chemistry for Jeremy

Question

Lesson 14 Stoichiometry Problems

1. The compound KClO₃ decomposes according to the following equation: 2KClO3 = 2KCl + 3O2

a. What is the mole ratio of KClO₃ to O₂ in this reaction?

b. How many moles of O₂ can be produced by letting 6.0 moles of KClO₃ react based on the above equation?

c. How many molecules of oxygen gas, O₂, are produced in question 1b?

2.Magnesium combines with chlorine, Cl₂, to form magnesium chloride, MgCl₂, during a synthesis reaction.

a.Write a balanced chemical equation for the reaction.

b. How many moles of magnesium chloride can be produced with 3 moles of chlorine

3.Ethanol burns according to the following equation. If 15.0 mol of C₂H₅OH burns this way, how many moles of 

oxygen are needed?

C2H5OH + 3O2 = 2CO2 + 3H2O

Answer 1

Solution:

Question 1:

The balanced chemical equation:

2KClO₃ → 2KCl + 3O₂

According to the equation above: n(KClO₃)/2 = n(KCl)/2 = n(O₂)/3

(a): Moles of KClO₃ : Moles of O₂ = 2 : 3

(b): n(O₂) = 3 × n(KClO₃) / 2 = (3 × 6.0 mol) / 2 = 9.0 mol

Moles of O₂ = 9.0 mol

(c): One mole of any substance contains 6.022×10²³ atoms/molecules.

Hence,

Number of O₂ molecules = (9.0 mol O₂) × (6.022×10²³ molecules / 1 mol O₂) = 5.42×10²⁴ O₂ molecules

Number of O₂ molecules = 5.42×10²⁴ molecules

Answers to Q1:

a) Moles of KClO₃ : Moles of O₂ = 2:3; b) Moles of O₂ = 9.0 mol; c) 5.42×10²⁴ molecules.

Question 2:

(a): The balanced chemical equation: Mg + Cl₂ → MgCl₂

(b): According to the equation above: n(Mg) = n(Cl₂) = n(MgCl₂)

Hence,

n(MgCl₂) = n(Cl₂) = 3.0 mol

Moles of MgCl₂ = 3.0 mol

Answers to Q2: a) Mg + Cl₂ → MgCl₂; b) Moles of MgCl₂ = 3.0 mol.

Question 3:

The balanced chemical equation:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

According to the equation above: n(C₂H₅OH) = n(O₂)/3 = n(CO₂)/2 = n(H₂O)/3

Hence,

n(O₂) = 3 × n(C₂H₅OH) = 3 × 15.0 mol = 45.0 mol

Moles of O₂ = 45.0 mol

Answer to Q3: Moles of O₂ = 45.0 mol.