Problem: First launch the video. The video will show you the Smart Figure. After watching the video, answer the related follow-up question. You can watch the video again or reference the Smart Figure in the book(Pages 193 - 193) at any point.This figure shows the gas phase reaction between methane, CH4, and chlorine, Cl2 to produce methyl chloride, CH3Cl and hydrogen chloride, HCl. Using the average bond enthalpies in the table below, estimate the Hrxn for the analogous gas phase reaction between methane, CH4, and bromine, Br2, to produce methyl bromide, CH3Br, and hydrogen bromide, HBr.TABLE 5.4 Average Bond Enthalpies (kJ/mol)C-H413N-H391O-H463F-F155C-C348N-N163O-O146C=C614N-O201O=O495Cl-F253C-N293N-F272O-F190Cl-Cl242C-O358N-Cl200O-Cl203C=O799N-Br243O-I234Br-F237C-F485Br-Cl218C-Cl328H-H436Br-Br193C-Br276H-F567C-I240H-Cl431I-Cl208H-Br366I-Br175H-I299I-I151

FREE Expert Solution

We’re being asked to determine the standard enthalpy change of formation (ΔH˚rxn) for the reaction:

CH4 + Br2 → CH3Br   +   HBr           Balanced Equation


Recall that ΔH˚rxn can be calculated from the bond enthalpies of the reactants and products involved


H°rxn = H°reactants - H°products



88% (72 ratings)
View Complete Written Solution
Problem Details

First launch the video. The video will show you the Smart Figure. After watching the video, answer the related follow-up question. You can watch the video again or reference the Smart Figure in the book(Pages 193 - 193) at any point.

A diagram shows enthalpy (H) on the Y-axis (increasing), with the reactants CH4 and Cl2 about one quarter of the way up the axis. 1) Break C-H and Cl-Cl bonds.  One of the C-H bonds in CH4 and the Cl-Cl bond in Cl2 are broken.  Delta-H1 is greater than 0, and the enthalpy has increased to the top of the Y-axis. 2) Make C-Cl and H-Cl bonds.  The free H bonds to Cl to make HCl and the remaining Cl bonds to C to make CH3Cl.  Delta-H2 is less than 0, and the enthalpy of the products decreases to the bottom of the Y-axis. The difference in enthalpy between the products and reactants is delta-H reaction.


This figure shows the gas phase reaction between methane, CH4, and chlorine, Cl2 to produce methyl chloride, CH3Cl and hydrogen chloride, HCl. Using the average bond enthalpies in the table below, estimate the Hrxn for the analogous gas phase reaction between methane, CH4, and bromine, Br2, to produce methyl bromide, CH3Br, and hydrogen bromide, HBr.


TABLE 5.4 Average Bond Enthalpies (kJ/mol)
C-H413N-H391O-H463F-F155
C-C348N-N163O-O146

C=C614N-O201O=O495Cl-F253
C-N293N-F272O-F190Cl-Cl242
C-O358N-Cl200O-Cl203

C=O799N-Br243O-I234Br-F237
C-F485



Br-Cl218
C-Cl328H-H436

Br-Br193
C-Br276H-F567



C-I240H-Cl431

I-Cl208


H-Br366

I-Br175


H-I299

I-I151



Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Enthalpy of Formation concept. You can view video lessons to learn Enthalpy of Formation. Or if you need more Enthalpy of Formation practice, you can also practice Enthalpy of Formation practice problems.