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Chapter Analysis
Intermediate32 pages • EnglishQuick Summary
Chapter 5 on Thermodynamics explores the fundamental concepts of thermodynamics, focusing on the laws governing energy changes in chemical reactions and processes. It covers key topics such as the first law of thermodynamics, state functions, enthalpy, and entropy, emphasizing their significance in determining the spontaneity of chemical reactions. The chapter introduces Gibbs energy as a crucial function for predicting reaction spontaneity and discusses its applications in various thermodynamic processes.
Key Topics
- •First law of thermodynamics
- •State functions: internal energy and enthalpy
- •Entropy and its significance
- •Gibbs energy and spontaneity
- •Applications of thermodynamics to chemical reactions
- •Enthalpy changes and Hess’s law
- •Types of thermodynamic systems
- •Equilibrium and thermodynamic stability
Learning Objectives
- ✓Explain the concepts of systems and surroundings in thermodynamics.
- ✓Apply the first law of thermodynamics to calculate energy changes.
- ✓Describe the relationship between enthalpy, entropy, and spontaneity.
- ✓Use Gibbs energy to predict the spontaneity of chemical reactions.
- ✓Differentiate between open, closed, and isolated systems.
- ✓Calculate and interpret enthalpy changes during chemical reactions.
Questions in Chapter
A thermodynamic state function is a quantity used to determine heat changes, whose value is independent of path, used to determine pressure volume work, whose value depends on temperature only.
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For the process to occur under adiabatic conditions, the correct condition is: ∆T = 0, ∆p = 0, q = 0, w = 0.
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The enthalpies of all elements in their standard states are unity, zero, < 0, different for each element.
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∆U of combustion of methane is – X kJ mol–1. The value of ∆H is = ∆U, > ∆U, < ∆U, = 0.
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The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are –890.3 kJ mol–1 –393.5 kJ mol–1, and –285.8 kJ mol–1 respectively. Enthalpy of formation of CH4(g) will be
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Additional Practice Questions
Explain the significance of Gibbs energy change in chemical reactions.
mediumAnswer: Gibbs energy change, or Gibbs free energy, is a thermodynamic property that indicates the maximum amount of reversible work a thermodynamic system can perform at constant temperature and pressure. It is used to predict the spontaneity of a process; a negative Gibbs energy change implies a spontaneous process.
What is the role of entropy in thermodynamics?
mediumAnswer: Entropy is a measure of the disorder or randomness of a system. In thermodynamics, it helps predict the feasibility of a process. An increase in total entropy indicates that a process is spontaneous, whereas a decrease suggests non-spontaneity.
Differentiate between endothermic and exothermic reactions in terms of enthalpy change.
easyAnswer: Endothermic reactions absorb energy from the surroundings, resulting in a positive enthalpy change, while exothermic reactions release energy, leading to a negative enthalpy change.
Describe the first law of thermodynamics and its significance.
mediumAnswer: The first law of thermodynamics, or the law of energy conservation, states that energy cannot be created or destroyed, only transformed from one form to another. It is significant in balancing the energy changes within chemical reactions and helps in calculating internal energy changes in systems.
How does temperature influence the spontaneity of a reaction according to thermodynamic principles?
mediumAnswer: Temperature affects spontaneity through the Gibbs energy equation where ∆G = ∆H - T∆S. If the entropy change is positive, increasing temperature can make non-spontaneous reactions spontaneous by increasing the T∆S term, thus reducing ∆G.