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: Calculate ΔHrxn for the following reaction:CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)Use the following reactions and given ΔH′s.C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJC(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7k

Solution: Calculate ΔHrxn for the following reaction:CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)Use the following reactions and given ΔH′s.C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJC(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7k

Problem

Calculate ΔHrxn for the following reaction:
CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)

Use the following reactions and given ΔH′s.
C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJ
C(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7kJ
H2(g) + Cl2(g) → 2HCl(g)   ΔH = −184.6kJ

Solution
  • For Hess's Law, we need to get the corresponding equation below using the sequence of reactions given

  • By manipulating the reaction, either reversing them or multiplying/dividing them to a certain factor, we can get to the target equation as well as the total enthalpy

CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)


C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJ (needs to reverse)

C(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7kJ (retain)

H2(g) + Cl2(g) → 2HCl(g)   ΔH = −184.6kJ (multiply by 2 to get 4Cl2 and cancel out 4 HCl and 4 H2)


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