Ch.6 - Thermochemistry WorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: 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-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C=C 614 N-O 201 O=O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 Cl-Cl 242 C-O 358 N-Cl 200 O-Cl 203 C=O 799 N-Br 243 O-I 234 Br-F 237 C-F 485 Br-Cl 218 C-Cl 328 H-H 436 Br-Br 193 C-Br 276 H-F 567 C-I 240 H-Cl 431 I-Cl 208 H-Br 366 I-Br 175 H-I 299 I-I 151

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.

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-H 413 N-H 391 O-H 463 F-F 155
C-C 348 N-N 163 O-O 146
C=C 614 N-O 201 O=O 495 Cl-F 253
C-N 293 N-F 272 O-F 190 Cl-Cl 242
C-O 358 N-Cl 200 O-Cl 203
C=O 799 N-Br 243 O-I 234 Br-F 237
C-F 485 Br-Cl 218
C-Cl 328 H-H 436 Br-Br 193
C-Br 276 H-F 567
C-I 240 H-Cl 431 I-Cl 208
H-Br 366 I-Br 175
H-I 299 I-I 151