Chapter 3B: The Second Law: The Entropy of the Universe Increases Flashcards
What is Gibbs free energy?
It’s defined as a combination of enthalpy (H), temperature (T), and entropy (S), given by the equation G = H - TS.
Used to determine whether a chemical reaction will happen on its own without external intervention such as external energy input. (i.e., spontaneously).
It applies to systems under constant T and p.
In biological systems, the change in free energy (ΔG) is particularly relevant because it represents the energy available to drive chemical reactions.
Is Gibbs free energy extensive or intensive?
Because G is specified by the state variables H, T, and S and because both H and TS are quantities that increase in proportion to the amounts of materials, the Gibbs free energy is an extensive variable of state and has the same units as enthalpy or energy.
-meaning it depends on the quantity or amount of the substances involved in the reaction.
If ΔG at constant T and p is negative what occurs? How about positive? Zero?
-If ΔG is negative (ΔG < 0), it means that the process can occur spontaneously under these conditions. In other words, the reaction will happen on its own without the need for external energy input.
-If ΔG is positive (ΔG > 0), the process will not occur spontaneously. External energy input is required for the reaction to proceed.
-If ΔG is zero (ΔG = 0), the system is at equilibrium. At this point, there is no net change occurring in the system, and the forward and reverse reactions are happening at equal rates.
Whats common for most chemical reactions?
-Large changes in energy and enthalpy
-Constant temperature and pressure are also
common conditions for life processes
What is —Wother, in relation to spontaneous and non spontaneous processes.
Thus, —Wother the maximum nonexpansion work a system can do on the surroundings, is
positive for a spontaneous process. From Eq. 3.28, it follows that -AG = -Wother
> O
for a spontaneous process at constant temperature and pressure, or
AG < 0 (spontaneous process at constant T and p).
(3.29)
If a process is not spontaneous, Wother must be positive and
AG > 0 (nonspontaneous process at constant T and p).
(3.30)
A system at equilibrium cannot perform any work. Thus, Wother
= 0and
AG = 0 (system at equilibrium at constant T and p).
(3.31)
Gibbs free energy change equation?
ΔG = ΔH - TΔS
Where:
ΔG is the change in Gibbs free energy.
ΔH is the change in enthalpy (heat) of the system.
T is the absolute temperature in Kelvin.
ΔS is the change in entropy of the system.
This equation is fundamental in thermodynamics and is used to determine whether a chemical reaction will occur spontaneously at a given temperature and pressure. Here’s what the terms represent:
If ΔG is negative (ΔG < 0), the reaction is spontaneous in the forward direction.
If ΔG is positive (ΔG > 0), the reaction is nonspontaneous in the forward direction and requires an input of energy to proceed.
If ΔG is zero (ΔG = 0), the system is at equilibrium, and there is no net change in the concentrations of reactants and products.
What are the two types of work?
break down the reversible work (dwrev) into two types: pressure-volume work (-pdV) associated with changes in the system’s volume (dV) and all other forms of work (dwother).
What is the equation for when a process occurs at constant temperature and pressure (dT = dp = 0)
the equation simplifies to ΔG = wother
ΔG (the change in Gibbs free energy) at constant pressure and temperature is equal to the nonexpansion work, denoted as Wother. This means ΔG = Wother.
-Wother is also known as?
Nonexpansion work, also known as the “other work” or “additional work” besides pressure-volume work, is the work done by a system in processes other than changes in volume. It includes various forms of work, such as electrical work in chemical reactions or other types of work depending on the system and process.
its the non-pv work obtained from a reversible process at constant temperature and pressure.
When is work done by a system maximal?
The work done by a system is maximal when a process is carried out reversibly. Therefore, -Wother (negative because work is done on the surroundings) is equal to -ΔG and represents the maximum amount of nonexpansion work a system can perform on the surroundings under conditions of constant temperature and pressure.
