Chemistry Chapter on Equilibrium and Free Energy

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Questions and Answers

What does the equation $ riangle G = riangle H - T riangle S$ signify in a thermodynamic context?

It signifies the change in Gibbs free energy is dependent on enthalpy changes and entropy changes at a constant temperature.

How is equilibrium established according to the Gibbs free energy relationship with equilibrium constant $K_{eq}$?

Equilibrium is established when $ riangle G$ equals zero, and $ riangle G^igcirc = -RT ext{ln} K_{eq}$ defines the relationship.

What is the significance of $ riangle G < 0$ in a chemical reaction?

It indicates that the reaction is spontaneous and can proceed without external energy input.

Given $ riangle G^igcirc$ for the conversion of G6P to F6P is 2.1 kJ mol−1, how do you compute the equilibrium concentrations of G6P and F6P?

Use the equation $0.0428 - 0.428x = x$ to solve for $x$, which gives [F6P] = 0.03M and [G6P] = 0.07M. Signup and view all the answers

Describe the implications of the second law of thermodynamics on spontaneous processes.

The second law implies that for any spontaneous process, the entropy of the universe increases, leading to irreversible changes in systems. Signup and view all the answers

What factors influence the spontaneity of a reaction as described by the equation $ riangle H - T riangle S < 0$?

The factors include the enthalpy change ($ riangle H$) and the entropy change ($ riangle S$), both of which are temperature dependent. Signup and view all the answers

Explain the role of the first law of thermodynamics in the context of enthalpy change.

The first law states that the change in internal energy is equal to heat added to the system plus work done on the system, emphasizing the conservation of energy. Signup and view all the answers

How does the concept of equilibrium apply to rate constants and reaction stability?

At equilibrium, the rates of the forward and reverse reactions are equal, resulting in a stable concentration of reactants and products. Signup and view all the answers

What does the expression $q_{irrev} < T riangle S$ imply about reversible and irreversible processes?

It implies that for irreversible processes, the heat exchanged is less than the product of temperature and change in entropy, indicating more disorder. Signup and view all the answers

What does the equation $ riangle G - riangle G^igcirc = RT ext{ln} K_{eq}$ tell us about non-equilibrium conditions?

It provides a relationship showing how the Gibbs free energy change of a system relates to the equilibrium constant when not at equilibrium. Signup and view all the answers

What does a negative Gibbs free energy ($, \Delta G < 0$) indicate about a thermodynamic process?

It indicates that the process is spontaneous and will proceed in the preferred direction. Signup and view all the answers

In the equation $, \Delta G = \Delta H - T\Delta S$, what role does temperature (T) play in determining spontaneity?

Temperature affects the contribution of the entropy change ($, \Delta S$) to the Gibbs free energy, influencing whether the process is enthalpy or entropy controlled. Signup and view all the answers

When is a process considered to be enthalpy controlled?

A process is enthalpy controlled when the $, \Delta H$ term is large and negative, dominating the Gibbs free energy equation. Signup and view all the answers

What does it mean when $, \Delta G = 0$?

It signifies that the system has reached equilibrium, and no net change occurs in the concentrations of reactants and products. Signup and view all the answers

For the reaction of ATP to ADP and Pi, what does a $, \Delta G^ riangle = -30.5 , kJ , mol^{-1}$ suggest about its energy profile?

It indicates that the reaction is exergonic, releasing energy that can be harnessed for cellular processes. Signup and view all the answers

Given $, \Delta H^ riangle = -20.1 , kJ , mol^{-1}$ for ATP hydrolysis, how do you calculate $, \Delta S^ riangle$?

Using the equation $, \Delta G^ riangle = \Delta H^ riangle - T\Delta S^ riangle$ at $37 , °C$, rearranged to find $, \Delta S^ riangle = \frac{, \Delta H^ riangle - , \Delta G^ riangle}{T}$. Signup and view all the answers

In the unfolding of a protein, what does a positive $, \Delta H^ riangle$ and a positive $, \Delta S^ riangle$ indicate?

It indicates that the process requires energy input (endothermic) but results in increased disorder, suggesting potential spontaneity at higher temperatures. Signup and view all the answers

What threshold must be exceeded for the unfolding of a protein (with $, \Delta H^ riangle = 250.8 , kJ , mol^{-1}$ and $, \Delta S^ riangle = 752 , J , K^{-1} , mol^{-1}$) to become spontaneous?

The temperature must exceed approximately $T = \frac{\Delta H}{\Delta S} = \frac{250800 , J}{752 , J , K^{-1}} \approx 333.3 , K$, or $60.3 , °C$. Signup and view all the answers

What does the complexation of Mg2+ with EDTA achieve in terms of Gibbs free energy?

The process is spontaneous with a negative $, \Delta G$, indicating that it proceeds to completion due to the significant increase in disorder. Signup and view all the answers

Study Notes

Equilibrium

Equilibrium is defined by equilibrium constants, Keq.
Equilibrium constants define the structure of systems.
A system at equilibrium is stable.
A system not at equilibrium is unstable.
There is a relationship between G and Keq.
At equilibrium, G° = −RTlnKeq.

Energy

The first law of thermodynamics states that H is the change in enthalpy.
The second law of thermodynamics states that S is the change in entropy.
The Gibbs free energy equation is G = H – TS.
A system is at equilibrium when G = 0.
Spontaneous changes occur when G < 0.

Free Energy

G° = −RTlnKeq is true at equilibrium only.
If a system is not at equilibrium, then G − G° = RTlnKeq.
G is the free energy of a system.
G° is the free energy of a process at equilibrium.

Free Energy Example

The standard free energy change (G°) for the isomerization of glucose-6-phosphate (G6P) to fructose-6-phosphate (F6P) is 2.1 kJ mol−1.
The concentrations of G6P and F6P at equilibrium at 25 °C, starting with 0.1 M G6P, are 0.07M for [G6P] and 0.03M for [F6P].

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic state function.
The Gibbs free energy equation is G = H − TS.
For any spontaneous process at constant T and P, G < 0.
A process reaches equilibrium when G = 0.

Enthalpy vs. Entropy

Enthalpy controlled processes are dominated by the H term where H is large and negative.
Entropy controlled processes are dominated by the TS term.
The analysis of Mg2+ using complexation by EDTA is an example of a process that is driven by entropy.

Standard States of Free Energies

G° is the value of G for a pure substance under 1 atmosphere of pressure at a specified temperature.
G° is the change in free energy when 1 mole of reactants in their standard states are converted to 1 mole of products in their standard states.

ATP, ADP and AMP

ATP, ADP and AMP are key molecules in biochemical energy transfer
The hydrolysis of ATP to ADP is a spontaneous process with a G° of −30.5 kJ mol−1.

Tutorial: G = H − TS

From the first law of thermodynamics: enthalpy H = qp= U + PV.
The enthalpy change concerns energy changes to the system during processes.
From the second law of thermodynamics: entropy S = q.
The entropy change concerns changes to the disorder of the system during processes.
The unfolding of a protein is an entropy driven process.

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Description

Explore the principles of equilibrium and free energy in this quiz, focusing on equilibrium constants, the laws of thermodynamics, and the relationship between Gibbs free energy and enthalpy. Understand how these concepts govern system stability and spontaneity. Test your knowledge on key equations and applications in chemistry.