Thermodynamics and Reaction Energy Flashcards
Students will be able to explain the principles of thermodynamics, including the First Law of Thermodynamics and the concepts of enthalpy, entropy, and Gibbs Free Energy. They will analyze the energy changes in chemical reactions, distinguishing between exothermic and endothermic processes, and predict reaction spontaneity using Gibbs Free Energy calculations. This includes applying these concepts to solve problems related to reaction energy and spontaneity.
What is the First Law of Thermodynamics?
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
This is also known as the Law of Conservation of Energy, which implies that the total energy of an isolated system remains constant, though it may change forms.
What is enthalpy (H) and how is it related to heat in a chemical reaction at constant pressure?
Enthalpy (H) is a measure of the total energy of a system, and in a chemical reaction at constant pressure, the change in enthalpy (∆H) is equal to the heat absorbed or released by the system.
Enthalpy is used to describe the heat flow in processes that occur at constant pressure, and ∆H can be positive (endothermic) or negative (exothermic).
Explain why exothermic reactions release energy, while endothermic reactions absorb energy.
In exothermic reactions, the energy released from forming new bonds is greater than the energy required to break the reactants’ bonds, resulting in a net release of energy. In endothermic reactions, more energy is required to break the bonds of the reactants than is released in forming new bonds, resulting in energy absorption.
Exothermic reactions have a negative ∆H, indicating heat release, while endothermic reactions have a positive ∆H, indicating heat absorption.
If a reaction has a negative ∆H and a positive ∆S, what can be said about the spontaneity of the reaction at any temperature?
The reaction will be spontaneous at any temperature because a negative ∆H (exothermic) and a positive ∆S (increase in disorder) both favor spontaneity.
According to Gibbs Free Energy ∆G = ∆H - T∆S, a negative ∆H and a positive ∆S ensure that ∆G is negative, indicating a spontaneous reaction.
Using Gibbs Free Energy, explain how temperature affects the spontaneity of a reaction with a positive ∆H and a positive ∆S.
For a reaction with both positive ∆H and positive ∆S, the spontaneity depends on temperature. At high temperatures, the T∆S term becomes large enough to outweigh the positive ∆H, making ∆G negative and the reaction spontaneous. At low temperatures, the reaction is nonspontaneous since ∆G will be positive.
Gibbs Free Energy determines reaction spontaneity through the equation ∆G = ∆H - T∆S. A large positive T∆S can make the reaction spontaneous at high temperatures, despite a positive ∆H.
