Textbook Question
Redraw the following diagram to represent the situation (b) when work has been lost by the system.
Ch.9 - Thermochemistry: Chemical Energy
McMurry8th EditionChemistryISBN: 9781292336145
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 9, Problem 38a
The reaction of A with B to give D proceeds in two steps: (1) A + B → C ΔH° = -20 kJ (2) C + B → D ΔH° = +50 kJ (3) A + 2B → D ΔH° = ? (a) Which Hess's law diagram represents the reaction steps and the overall reaction? Diagram 1 Diagram 2
Verified step by step guidance1
Identify the individual reactions and their respective enthalpy changes given in the problem. The first reaction is A + B → C with an enthalpy change ΔH° = -20 kJ. The second reaction is C + B → D with an enthalpy change ΔH° = +50 kJ.
Understand that Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for any set of steps that leads from the reactants to the products. This means you can add the enthalpy changes of the steps to find the overall enthalpy change for the reaction A + 2B → D.
Add the enthalpy changes of the two steps. Since the first step has an enthalpy change of -20 kJ and the second step has an enthalpy change of +50 kJ, sum these values to find the overall enthalpy change for the reaction A + 2B → D.
Choose the correct Hess's law diagram that represents the given reactions and the overall reaction. The diagram should show the first reaction leading to the formation of C, the second reaction using C to form D, and the overall reaction directly forming D from A and 2B.
Verify that the diagram correctly aligns with the steps and the enthalpy changes provided, ensuring that it visually represents the sum of the enthalpy changes from the individual steps to the overall reaction.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hess's Law
Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows chemists to calculate the overall enthalpy change for a reaction by adding the enthalpy changes of each step, making it essential for analyzing multi-step reactions.
Recommended video:
Guided course
02:03
Hess's Law
Enthalpy Change (ΔH)
Enthalpy change (ΔH) is a measure of the heat content of a system at constant pressure. A negative ΔH indicates an exothermic reaction, where heat is released, while a positive ΔH indicates an endothermic reaction, where heat is absorbed. Understanding these changes is crucial for predicting the energy dynamics of chemical reactions.
Recommended video:
Guided course
02:34Enthalpy of Formation
Reaction Mechanism
A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. Each step has its own rate and enthalpy change, and understanding the mechanism helps in visualizing how reactants are converted to products, which is vital for applying Hess's Law to find the overall reaction enthalpy.
Recommended video:
Guided course
03:06Reaction Mechanism Overview
Related Practice
Textbook Question
Redraw the following diagram to represent the situation (a) when work has been gained by the system and
2
views
Textbook Question
The reaction of A with B to give D proceeds in two steps: (1) A + B → C ΔH° = -20 kJ (2) C + B → D ΔH° = +50 kJ (3) A + 2B → D ΔH° = ? (b) What is the value of ΔH° for the overall reaction A + 2 B → D ΔH° = ?
Textbook Question
The following reaction is exothermic:
(a) Write a balanced equation for the reaction (red spheres represent A atoms and ivory spheres represent B atoms)
Textbook Question
A reaction is carried out in a cylinder fitted with a movable piston. The starting volume is V = 5.00 L, and the appa- ratus is held at constant temperature and pressure. Assum- ing that ∆H = -35.0 kJ and ∆E = -34.8 kJ, redraw the piston to show its position after reaction. Does V increase,decrease, or remain the same?
Textbook Question
Acetylene, C2H2, reacts with H2 in two steps to yield ethane, CH3CH3:(1) HC?CH + H2 → H2C?CH2 ΔH° = -175.1 kJ(2) H2C?CH2 + H2 → CH3CH3 ΔH° = -136.3 kJWhich arrow (a–c) in the Hess's law diagram corresponds to which step, an2d which a2rrow cor2responds to the net reaction? Where are the reactants located on the diagram, and where are the products located?