What is Gibbs free energy: Definition and 121 Discussions
In thermodynamics, the Gibbs free energy (or Gibbs energy) is a thermodynamic potential that can be used to calculate the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. The Gibbs free energy (
Δ
G
=
Δ
H
−
T
Δ
S
{\displaystyle \Delta G=\Delta H-T\Delta S}
, measured in joules in SI) is the maximum amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter). This maximum can be attained only in a completely reversible process. When a system transforms reversibly from an initial state to a final state, the decrease in Gibbs free energy equals the work done by the system to its surroundings, minus the work of the pressure forces.The Gibbs energy (symbol
G
{\displaystyle G}
) is also the thermodynamic potential that is minimized when a system reaches chemical equilibrium at constant pressure and temperature. Its derivative with respect to the reaction coordinate of the system vanishes at the equilibrium point. As such, a reduction in
G
{\displaystyle G}
is necessary for a reaction to be spontaneous at constant pressure and temperature.
The Gibbs free energy, originally called available energy, was developed in the 1870s by the American scientist Josiah Willard Gibbs. In 1873, Gibbs described this "available energy" as
the greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition.
The initial state of the body, according to Gibbs, is supposed to be such that "the body can be made to pass from it to states of dissipated energy by reversible processes". In his 1876 magnum opus On the Equilibrium of Heterogeneous Substances, a graphical analysis of multi-phase chemical systems, he engaged his thoughts on chemical-free energy in full.
If the reactants and products are all in their thermodynamic standard states, then the defining equation is written as
Homework Statement
You have two parts of a tank, divided by a divider. On the larger side, you have 4 mol of N2 gas and on the smaller side you have 1 mol O2 gas. Both gasses are are the same T and P. The divider is removed and the gasses mix.
What is the final T and P?
What is the...
Thermodynamics: Gibbs free energy from this "battery" reaction?
Homework Statement
I'm reading my textbook and it gives an example.
The dH of the reaction is -316kJ/mol so that much energy is released by the reaction itself. Additionally, the entropy of the products are higher than the...
Homework Statement
Do a qualitative sketch of a G vs T (and G vs P) graph for water at liquid, solid and gas phases at atmospheric pressure. How would the graphs differ at a pressure of 0.001 bar/slightly higher temperatures?
Homework Equations
None that I can think of.
The Attempt at a...
Homework Statement
There are a problems I wasn't sure about on my test. Trying to get answers for ones I had to guess on.
1. What is the maximum [Mg] that can be achieved in an aqueous solution of Mg(OH)2 with a pH=12.50? Ksp (Mg(OH)2)=5.6e-12
2. Determine the max solubility of CaF2...
Homework Statement
I'm having some difficulty with this question, not exactly sure how to start it. Any suggestion would help. Thanks
At 2.02 atm water boils at 121 °C. Calculate the change in the Gibbs free energy
when one mole of steam at 121 °C and one atm condenses to liquid water at...
the total amount of energy able to do work is the gibbs free energy of a reaction.
dG=dH-TdS
according to this equation, the higher the entropy gain of a system(dS) in a reaction, the more work the system can achieve. I'm confused here. I thought entropy was the energy unable to do work?
Hi, I've recently started studying chemistry and have being going over gibbs free energy.. I understand it is a driving force causing chemical and physical changes but during my course of reading I did have some queries stem to mind.
1) In relation to equilibrium why is it that a reaction...
Homework Statement
Suppose you have a mole of water at 198 K. and atmospheric pressure. use the data at the bac of this book to determine what happens to its gibbs free energy if you raise the temperature to 303 Kelvins. To compensate for this change, you could increase the pressure of the...
Homework Statement
The reaction is NH_{4}Cl(s)\rightarrow NH_{3}(g)+HCl(g)
\Delta H^{o}=+176 kJ and \Delta G^{o}=+91.2 kJ at 298 K
What is the value of \Delta G at 1000 K?
Homework Equations
\Delta G=\Delta H-T\Delta S
The same applies if all 'deltas' are standard
The Attempt at...
Homework Statement
CaCO3 <-> CaO + CO2
At 900K, equilibrium pressure of CO2 is 0.0423 atm. Calculate Gibbs Free energy of Reaction and K.Homework Equations
delta G = -RTlnKThe Attempt at a Solution
delta G = 5656.3 cal/mol
K = 0.0423
I have a feeling that this is incorrect
Could someone...
Hi,
I'm trying to answer a question that I'm stuck on. The question is as follows:
--------------------------------------------------------------
If the Gibbs free energy change (deltaG) for ATP hydrolysis in a cell is -57 kJ/mol and the free energy change for transporting a proton from...
Homework Statement
A. Explain the need for Gibbs Free Energy equation.
B. Explain what it means when:
\Delta G <0 \Delta G >0 \Delta G =0
Homework Equations
\Delta G= \Delta H-T \Delta S
The Attempt at a Solution
A. Gibbs eqn comes from the need to calculate the entropy of...
Hey guys, I'm hung up on the Gibbs Free Energy equations. I know that ?G° is the free energy change under standard conditions (1 M, 1 atm, 25ºC), and that it is characteristic for a given reaction. I think that when a reaction is occurring under conditions that are not standard the equation...
Homework Statement
Calculate the Gibbs free energy for a van der Waals gas (up to an integration constant), assuming a fixed amount of material and temperature.
Homework Equations
P = \frac{NkT}{V-Nb} - \frac{aN^2}{V^2}
dG = -SdT + VdP + udN (where u is the chemical potential)
The...
Homework Statement
Consider fuel cell using methane as fuel. Reaction is
CH^4 + 2O_2 -> 2H2O+CO_2
Assume room temperature and atmospheric temperature
Determine values of delta H (Helmholtz) and delta G (Gibbs) for this reaction for one mole of methane.
Question instructed the use of...
Hi
I am new in thermodynamics , and I thought you can help me
If it is valid dG=dW
May I say
dG=-Pdv
P=-dG/dv?
thanks in advance,Mariana
P=external pressure
G=Gibbs energy
W=maximum work
I don't know where to start with this problem. I must be missing an equation or something...
Q: Pb(s)+2H^{+}(aq)\rightarrow Pb^{2+}(aq)+H_2(g) \,\,\,\,\,\,\,\,E^{\degree}_{cell}=+0.126V
What is the \Delta G^{\degree} in \frac{kJ}{mol} for this reaction.
a) -24
b) 24
c) -12
d) 12
e) 50...
would anyone happen to know what the expression for an isothermal change in Gibbs free energy for a liquid is when the pressure changes from pi to pf. Also an expression for when its a perfect gas?
i can't seem to figure them out.. and how would they be deduced?
i've come across one equation...
hey i seem to be having a lot of trouble with this type of question:
Calculate the change in Gibbs energy of 35g of ethanol (mass density = 0.789g cm-3) when the pressure is increased isothermally from 1 atm to 3000 atm.
in my notes i have that dG=V(Pf-Pi) and search up on the net that...