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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
Nature of Energy
Kinetic & Potential Energy
First Law of Thermodynamics
Internal Energy
Endothermic & Exothermic Reactions
Heat Capacity
Constant-Pressure Calorimetry
Constant-Volume Calorimetry
Thermal Equilibrium
Thermochemical Equations
Formation Equations
Enthalpy of Formation
Hess's Law
Additional Guides
Enthalpy (IGNORE)

Hess's Law involves the use of partial reactions in the determination of the overall enthalpy of reaction.

Hess's Law

Concept #1: Rearrangement of Thermochemical Equations

Multiplication of the original reaction results in multiplication of ∆Hrxn.

Division results in the division of ∆Hrxn..

Reversing the original reaction results in reversing the sign of ∆Hrxn.

Example #1: If the formation equation for boron trioxide is given as the following: 

What will be the new enthalpy value when it is rearranged? 

Practice: Calculate the ∆Hrxn for the following thermochemical equation: 

When given the following: 

Concept #2: Applying Hess’s Law

Addition of ∆Hrxn values of multiple steps gives us the ∆Hrxn of the overall reaction.

Example #2: Calculate the ∆Hrxn for overall reaction:

When given the following set of partial reactions:

Practice: Calculate the ∆Hrxn for 

Given the following set of reactions: 

Practice: Calculate the ∆Hrxn for 

Given the following reactions: