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: For the following reaction, what is ∆H° when 25.0 g of Na2O2(molar mass = 77.98 g mol−1) is reacted with water?2 Na2O2(s) + 2 H2O(l) → 4 NaOH(s) + O2(g)         ∆H° = −126 kJ(A) -20.2 kJ (B) 87.4 kJ (C) -126 kJ (D) 20.2 kJ (E) -87.4 kJ

Problem

For the following reaction, what is ∆H° when 25.0 g of Na2O2(molar mass = 77.98 g mol−1) is reacted with water?

2 Na2O2(s) + 2 H2O(l) → 4 NaOH(s) + O2(g)         ∆H° = −126 kJ

(A) -20.2 kJ 

(B) 87.4 kJ 

(C) -126 kJ 

(D) 20.2 kJ 

(E) -87.4 kJ

Solution

Use the concept of thermochemistry and stoichiometry to determine ΔH of the reaction of 25 g Na2O2 upon reaction with water

It can be seen that 2 moles of Na2O2 produces -126 kJ of heat.

Calculating for the ΔH of the reaction:

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