TERMOQUIMICA Teoría 1: Introducción a la termodinámica química. Sistemas termodinámicos.

Understanding Thermodynamics and Energy Conservation

Introduction to Thermodynamics

• The science that studies energy in its various manifestations is known as thermodynamics.

• Thermodynamics examines energy transformations, particularly in chemical reactions.

Key Laws of Chemistry

• The study of a chemical reaction is crucial for defining the reaction's characteristics.

• The law of conservation of mass states that matter cannot be created or destroyed during a chemical reaction.

Conservation Principles

• In a reaction, if reactant A completely transforms into product B, the total mass remains constant.

• Similarly, the law of conservation of energy asserts that energy cannot be created or destroyed; it can only be transferred or transformed.

First Principle of Thermodynamics

• This principle emphasizes that energy transfer occurs in all chemical reactions, leading to variations in energy levels between reactants and products.

• Energy changes are expressed as delta E (ΔE), indicating the difference in energy before and after a reaction.

Types of Energy Changes

• Chemical reactions may involve different types of energy changes, such as light (luminous energy).

• For example, galvanic cells convert chemical reactions into electrical energy.

Energy Transfer and System Boundaries

Defining Systems and Surroundings

• In studying thermodynamic systems, boundaries can be physical (like a glass container) or imaginary (as with combustion processes).

Imaginary Boundaries in Reactions

• When analyzing reactions without physical walls (e.g., fire), one must define an imaginary boundary around the system for study purposes.

Example: Fire as a System

Thermodynamic Systems Classification

Understanding Thermodynamic Systems

• The study begins with defining the environment and system in thermodynamics, emphasizing that not all thermodynamic systems are identical.

• Thermodynamic systems are classified based on their ability to transfer material and energy, leading to three main types: open systems, closed systems, and isolated systems.

Types of Thermodynamic Systems

Open Systems

• An open system allows for the exchange of both matter and energy with its surroundings. For example, a chemical reaction producing gas can release it into the environment.

• In an open system, the universe is viewed as a portion under study while everything surrounding it constitutes the environment.

Closed Systems

• A closed system permits energy transfer but restricts matter exchange. An example includes heating milk in a sealed glass bottle in a microwave; heat can enter or leave but not the milk itself.

• The walls of a closed system may be real (like glass) or imaginary (conceptual boundaries), allowing for thermal energy exchange without material transfer.

Isolated Systems

• Isolated systems do not allow any transfer of matter or energy. They represent extreme cases where no interaction occurs with the surroundings.

Additional Classifications

• Beyond basic classifications, thermodynamic reactions can also be categorized based on physical states (gases, solids, liquids).

• The state of aggregation plays a crucial role in understanding how components interact within these systems during reactions.

Examples and Applications

• A practical illustration involves methane combustion where gaseous reactants produce gaseous products while transferring heat through diathermic vessel walls.

Thermodynamic Systems and Their Classifications

Understanding Heat Transfer in Thermodynamic Systems

• The discussion begins with the concept of heat release during reactions, indicating that energy transfer occurs within an open system, allowing both heat and matter exchange.

• In contrast, a closed system is introduced, which does not allow for matter exchange but can still transfer energy.

Types of Thermodynamic Systems

Open vs. Closed Systems

• A closed system exchanges energy but not matter; for example, a sealed bottle can allow thermal energy to escape while retaining its contents.

Isolated Systems

• An isolated system permits no exchange of either matter or energy. This is exemplified by a thermos (or "vaso de hualo"), which retains temperature without losing liquid or vapor.

• It is noted that truly isolated systems are theoretical since some minimal energy exchange always occurs in practice.

Classification Based on State of Matter

Homogeneous vs. Heterogeneous Systems

• Chemical reactions can be classified based on the state of aggregation (solid, liquid, gas) of reactants and products.

• A homogeneous system contains all components in the same state; for instance, when methane gas combusts with oxygen gas to produce carbon dioxide and water vapor—all gaseous states.