Nitrogen in air reacts at high temperatures to form NO2 according to the following reaction: N2 + 2 O2 → 2 NO2 b. Estimate ∆H for this reaction (in kcal and kJ) using the bond energies from Table 7.1.

Ch.7 Chemical Reactions: Energy, Rate and Equilibrium

McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition

McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook

All textbooks

McMurry 8th Edition

Ch.7 Chemical Reactions: Energy, Rate and Equilibrium

Problem 28b

Chapter 7, Problem 28b

Nitrogen in air reacts at high temperatures to form NO₂ according to the following reaction: N₂ + 2 O₂ → 2 NO₂
b. Estimate ∆H for this reaction (in kcal and kJ) using the bond energies from Table 7.1.

Verified step by step guidance

Identify the bonds broken and formed in the reaction. In the reactants, the bonds broken are one N≡N triple bond in N₂ and two O=O double bonds in O₂. In the products, the bonds formed are four N–O bonds in 2 NO₂ molecules.

Write the bond energy values for each bond involved. For example, the bond energy of N≡N is approximately 941 kJ/mol, the bond energy of O=O is approximately 498 kJ/mol, and the bond energy of N–O is approximately 201 kJ/mol. (Refer to Table 7.1 for exact values.)

Calculate the total energy required to break the bonds in the reactants. Multiply the bond energy of each bond by the number of bonds broken and sum them: Total energy for bonds broken = (1 × N≡N bond energy) + (2 × O=O bond energy).

Calculate the total energy released when bonds are formed in the products. Multiply the bond energy of each bond by the number of bonds formed and sum them: Total energy for bonds formed = (4 × N–O bond energy).

Determine the enthalpy change (∆H) for the reaction using the formula: ∆H = Total energy for bonds broken - Total energy for bonds formed. Convert the result from kJ to kcal if needed (1 kcal = 4.184 kJ).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

11m

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bond Energies

Bond energies represent the amount of energy required to break a bond between two atoms in a molecule. In the context of chemical reactions, these values are crucial for calculating the overall energy change (∆H) during the reaction. By summing the bond energies of the reactants and subtracting the bond energies of the products, one can estimate the enthalpy change associated with the reaction.

Enthalpy Change (∆H)

Enthalpy change (∆H) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ∆H < 0) or endothermic (absorbs heat, ∆H > 0). Calculating ∆H using bond energies allows chemists to predict the energy dynamics of a reaction, which is essential for understanding reaction feasibility and conditions.

Stoichiometry of the Reaction

Stoichiometry involves the quantitative relationships between the reactants and products in a chemical reaction. In the given reaction, the coefficients indicate the molar ratios of nitrogen and oxygen reacting to form nitrogen dioxide. Understanding stoichiometry is vital for accurately applying bond energies and calculating the total energy change, as it ensures that the correct number of bonds is considered in the energy calculations.

Recommended video:

Guided course

01:16

Stoichiometry

Related Practice

Textbook Question

Acetylene (H–C≡C–H) is the fuel used in welding torches.

b. Estimate ∆H for this reaction (in kJ/mol) using the bond energies listed in Table 7.1.

Textbook Question

The vaporization of Br₂ from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).

c. How many kilojoules are needed to evaporate 82 g of Br₂?

Textbook Question

Converting liquid water to solid ice releases 1.44 kcal/mol (6.02 kJ/mol).How many kilocalories are released by freezing 32 g of H2O?

Textbook Question

Which of the following processes results in an increase in entropy of the system?

a. A drop of ink spreading out when it is placed in water

b. Steam condensing into drops on windows

c. Constructing a building from loose bricks

Textbook Question

Glucose, also known as "blood sugar" when measured in blood, has the formula C₆H₁₂O₆.

a. Write the equation for the combustion of glucose with O₂ to give CO₂ and H₂O.

Textbook Question

Glucose, also known as "blood sugar" when measured in blood, has the formula C₆H₁₂O₆.

c. What is the minimum amount of energy (in kJ) a plant must absorb to produce 15.0 g of glucose?

views