Thermodynamics Flashcards

Which factor affects the spontaneity of a reaction?

Answer: The change in Gibbs free energy

The spontaneity of a chemical reaction, meaning whether it will occur without continuous external energy input, is primarily determined by the change in Gibbs free energy (ΔG). A negative ΔG indicates a spontaneous reaction, while a positive ΔG indicates a non-spontaneous reaction. Gibbs free energy combines both the enthalpy (heat change) and entropy (disorder change) of a system to provide a comprehensive criterion for spontaneity at constant temperature and pressure.

What is the definition of standard state conditions?

Answer: A reference state for a substance at a defined temperature, pressure, and concentration

Standard state conditions define a specific set of reference conditions for substances, allowing for consistent comparison of thermodynamic properties like enthalpy, entropy, and Gibbs free energy. For gases, this typically means 1 atmosphere pressure; for solutions, 1 M concentration; and for pure solids and liquids, their most stable form at 1 atmosphere pressure. While temperature is often specified (e.g., 25°C), the core definition establishes a uniform baseline for thermodynamic calculations.

In a spontaneous exothermic reaction, what happens to the Gibbs free energy?

Answer: It decreases

For any spontaneous process, the change in Gibbs free energy (ΔG) must be negative, indicating that the system's free energy decreases. An exothermic reaction releases heat (ΔH < 0). When an exothermic reaction is also spontaneous, it means the overall free energy of the system is reduced, making the process energetically favorable and able to proceed without external energy input.

What is meant by the term 'heat capacity'?

Answer: The amount of heat required to raise the temperature of a substance by a given amount

Heat capacity is a fundamental physical property that quantifies the amount of heat energy required to raise the temperature of a given substance by a specific amount, typically one degree Celsius or one Kelvin. Substances with high heat capacity require more energy to change their temperature, while those with low heat capacity heat up or cool down more quickly. It is a measure of a substance's ability to store thermal energy.

Which statement accurately describes endothermic reactions?

Answer: Reactions that absorb heat from their surroundings

Endothermic reactions are chemical processes that absorb heat energy from their surroundings. This absorption of heat causes the temperature of the surroundings to decrease, as energy is drawn into the reacting system. The enthalpy change (ΔH) for endothermic reactions is positive, indicating an increase in the system's internal energy.

What is an adiabatic process?

Answer: A process in which no heat is exchanged with the surroundings

An adiabatic process is a thermodynamic process in which no heat is transferred into or out of the system. This means the system is perfectly insulated from its surroundings, or the process occurs so rapidly that there is no time for significant heat exchange. Any change in the internal energy of the system during an adiabatic process is solely due to work done on or by the system.

What does the sign of the change in entropy indicate about a reaction?

Answer: Whether the reaction produces more disorder or order

The sign of the change in entropy (ΔS) indicates whether a reaction or process leads to an increase or decrease in the disorder or randomness of a system. A positive ΔS signifies an increase in disorder, meaning particles and energy become more dispersed. Conversely, a negative ΔS indicates an increase in order or a decrease in randomness within the system.

What is a state function in thermodynamics?

Answer: A property that depends only on the current state of a system, regardless of how the system reached that state

A state function in thermodynamics is a property of a system whose value depends only on the current state of the system, defined by variables like temperature, pressure, and volume. Crucially, its value is independent of the pathway or history by which the system arrived at that state. Examples include internal energy, enthalpy, entropy, and Gibbs free energy.

Why is it important to consider entropy when predicting the spontaneity of a reaction?

Answer: Entropy represents the dispersal of energy and particles in a system

Entropy is critical for predicting reaction spontaneity because it quantifies the natural tendency of systems to move towards greater disorder and dispersal of energy and particles. The second law of thermodynamics states that spontaneous processes tend to increase the total entropy of the universe. Gibbs free energy, which determines spontaneity, incorporates both enthalpy (energy change) and entropy (disorder change) to provide a complete picture of reaction favorability.

What does the change in enthalpy represent?

Answer: The heat transferred during a process at constant pressure

The change in enthalpy (ΔH) represents the heat transferred during a process that occurs at constant pressure. It is a key thermodynamic quantity used to characterize chemical reactions and physical changes. A negative ΔH indicates an exothermic process where heat is released, while a positive ΔH indicates an endothermic process where heat is absorbed.

A scientist can measure the temperature increase in a solution over time when heating it. Which of the following descriptions best describes the solution at this time?

Answer: The velocity of molecules in the solution is increasing

Temperature is a direct measure of the average kinetic energy of the particles within a substance. As a solution is heated, its molecules absorb thermal energy, which translates into increased kinetic energy. This increased kinetic energy causes the molecules to move faster, meaning their average velocity increases, leading to a measurable rise in temperature.

What is the main focus of thermodynamics?

Answer: Understanding how energy is transferred between systems and their surroundings

Thermodynamics is the branch of physics that studies how energy is transferred and transformed within and between systems and their surroundings. Its main focus is on understanding the relationships between heat, work, temperature, and energy, and how these factors govern the behavior of physical and chemical processes. It provides fundamental laws that describe energy conservation and the direction of spontaneous changes.

Enthalpy is a measure of?

Answer: The total energy of a system

Enthalpy (H) is a thermodynamic property that represents the total heat content of a system at constant pressure. It includes the system's internal energy plus the product of its pressure and volume. While often discussed in terms of its change (ΔH) during a process, enthalpy fundamentally quantifies the total energy associated with a system under these conditions.

Which statement best describes entropy?

Answer: A measure of the disorder or randomness of a system

Entropy (S) is a fundamental thermodynamic property that serves as a quantitative measure of the disorder, randomness, or dispersal of energy and matter within a system. The second law of thermodynamics states that the total entropy of an isolated system tends to increase over time for spontaneous processes. A higher entropy value indicates a greater degree of molecular chaos or energy distribution.

According to the first law of thermodynamics, energy is?

Answer: Conserved and cannot be created or destroyed

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed. It can only be transformed from one form to another or transferred between systems and their surroundings. This means that the total amount of energy in an isolated system remains constant, even as it undergoes various changes.

What does Gibbs free energy represent?

Answer: The energy available in a system to do useful work

Gibbs free energy (G) is a thermodynamic potential that represents the maximum amount of non-expansion work that can be extracted from a closed system at constant temperature and pressure. Essentially, it quantifies the energy available in a system to do useful work. A decrease in Gibbs free energy (ΔG < 0) indicates a spontaneous process that can perform work.