Skip to main content
Ch.14 - Chemical Kinetics
Chapter 14, Problem 121a

The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (a) Calculate the overall standard enthalpy change for the reaction process.

Verified step by step guidance
1
Identify the balanced chemical equation for the reaction: \(4 \text{HBr} + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} + 2 \text{Br}_2\).
Determine the standard enthalpy of formation (\(\Delta H_f^\circ\)) for each reactant and product from a reliable source, such as a chemistry textbook or database.
Use the formula for the standard enthalpy change of the reaction: \(\Delta H_{reaction}^\circ = \sum \Delta H_f^\circ (\text{products}) - \sum \Delta H_f^\circ (\text{reactants})\).
Calculate the sum of the standard enthalpies of formation for the products: \(2 \times \Delta H_f^\circ (\text{H}_2\text{O}) + 2 \times \Delta H_f^\circ (\text{Br}_2)\).
Calculate the sum of the standard enthalpies of formation for the reactants: \(4 \times \Delta H_f^\circ (\text{HBr}) + 1 \times \Delta H_f^\circ (\text{O}_2)\), and then subtract the reactants' sum from the products' sum to find the overall \(\Delta H_{reaction}^\circ\).

Verified Solution

Video duration:
4m
This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

Key Concepts

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

Standard Enthalpy Change

Standard enthalpy change (ΔH°) refers to the heat change that occurs at constant pressure when reactants are converted to products under standard conditions (1 atm pressure and a specified temperature, usually 25°C). It is a crucial concept in thermodynamics, allowing chemists to predict the energy changes associated with chemical reactions.
Recommended video:
Guided course
02:34
Enthalpy of Formation

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows for the calculation of enthalpy changes for complex reactions by breaking them down into simpler steps for which enthalpy values are known.
Recommended video:

Bond Enthalpies

Bond enthalpy is the energy required to break one mole of a specific type of bond in a gaseous molecule. Understanding bond enthalpies is essential for calculating the overall enthalpy change of a reaction, as it involves summing the energies required to break bonds in the reactants and the energies released when forming bonds in the products.
Recommended video:
Guided course
02:34
Enthalpy of Formation
Related Practice
Textbook Question

The reaction between ethyl iodide and hydroxide ion in ethanol 1C2H5OH2 solution, C2H5I1alc2 + OH- 1alc2 ¡ C2H5OH1l2 + I - 1alc2, has an activation energy of 86.8 kJ>mol and a frequency factor of 2.10 * 1011 M-1 s-1. (c) Which reagent in the reaction is limiting, assuming the reaction proceeds to completion?

807
views
Textbook Question

The reaction between ethyl iodide and hydroxide ion in ethanol 1C2H5OH2 solution, C2H5I1alc2 + OH- 1alc2 ¡ C2H5OH1l2 + I - 1alc2, has an activation energy of 86.8 kJ>mol and a frequency factor of 2.10 * 1011 M-1 s-1. (d) Assuming the frequency factor and activation energy do not change as a function of temperature, calculate the rate constant for the reaction at 50 C.

532
views
Textbook Question

The gas-phase reaction of NO with F2 to form NOF and F has an activation energy of Ea = 6.3 kJ>mol. and a frequency factor of A = 6.0 * 108 M-1 s-1. The reaction is believed to be bimolecular: NO1g2 + F21g2 ¡ NOF1g2 + F1g2 (e) Suggest a reason for the low activation energy for the reaction.

793
views
Textbook Question

The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (c) Draw a plausible Lewis structure for the intermediate HOOBr. To what familiar compound of hydrogen and oxygen does it appear similar?

630
views
Textbook Question

The rates of many atmospheric reactions are accelerated by the absorption of light by one of the reactants. For example, consider the reaction between methane and chlorine to produce methyl chloride and hydrogen chloride: Reaction 1: CH41g2 + Cl21g2 ¡ CH3Cl1g2 + HCl1g2 This reaction is very slow in the absence of light. However, Cl21g2 can absorb light to form Cl atoms: Reaction 2: Cl21g2 + hv ¡ 2 Cl1g2 Once the Cl atoms are generated, they can catalyze the reaction of CH4 and Cl2, according to the following proposed mechanism: Reaction 3: CH41g2 + Cl1g2 ¡ CH31g2 + HCl1g2 Reaction 4: CH31g2 + Cl21g2 ¡ CH3Cl1g2 + Cl1g2 The enthalpy changes and activation energies for these two reactions are tabulated as follows: Reaction H 1kJ ,mol 2 Ea 1kJ ,mol 2 3 +4 17 4 -109 4 (b) By using the data tabulated here, sketch a quantitative energy profile for the catalyzed reaction represented by reactions 3 and 4.

424
views
Textbook Question

Many primary amines, RNH2, where R is a carboncontaining fragment such as CH3, CH3CH2, and so on, undergo reactions where the transition state is tetrahedral. (a) Draw a hybrid orbital picture to visualize the bonding at the nitrogen in a primary amine (just use a C atom for 'R').

763
views