AP Chemistry help » Thermochemistry and also Kinetics » Thermodynamics » Gibbs free Energy and Spontaneity

Suppose the a rxn has ∆H = -28 kJ and ∆S= -60 J/K. At what temperature will certainly it change from spontaneous come non-spontaneous?


Explanation:

Approximately 467 K. ∆G=∆H-T∆S and a rxn proceeds spontaneously when ∆G and also is non-spontaneous when ∆G > 0. So if we set ∆G=0 and solve the equation for T, us will see that the crossover from spontaneous to non-spontaneous occurs when T=467K.

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If the reaction quotient (Q) is higher than the equilibrium constant (K), what is true about the Gibbs cost-free energy?


Explanation:

If Q is greater than K, the reaction has actually exceeded the equilibrium state. The will continue nonspontaneously (since equilibrium has already been reached), and this must typical that the ΔG (gibbs complimentary energy) should be positive, or greater than zero. 


The reaction will certainly be voluntary if and also only if the size of the enthalpy is better than the size of the entropy times the temperature


The reaction will certainly be spontaneous if and only if the size of the entropy is higher than the magnitude of the enthalpy time the temperature


The reaction will be voluntary if and only if the size of the enthalpy is greater than the magnitude of the entropy


Correct answer:

The reaction will certainly be spontaneous if and also only if the magnitude of the enthalpy is better than the size of the entropy time the temperature


Explanation:

A reaction is voluntary if the Gibb"s totally free Energy the the reaction is negative.

*

If

*
, the enthalpy, and
*
, the entropy, are both negative, then the reaction will be voluntarily if and only if the magnitude of the enthalpy is higher than the size of the entropy time the temperature.


Explanation:

The Gibb"s totally free energy equation is used to determine the spontaneity that a reaction and is written as follows:

*
.

*
is Gibb"s cost-free energy, 
*
is enthalpy, and 
*
is entropy. In order for a reaction to it is in spontaneous, Gibb"s totally free energy must have a an unfavorable value. Based on the equation, we have the right to see that a positive enthalpy in mix with a an adverse entropy will certainly always result in a confident value for Gibb"s totally free energy.

*

*

This method these room the problems that will always result in a nonspontaneous reaction. 


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Example inquiry #5 : Gibbs cost-free Energy and Spontaneity


Consider the adhering to reaction in a galvanic cell:

*


Which if the following statements around the reaction is false?


Possible Answers:

The cell potential is positive


The reaction is spontaneous


The equilibrium consistent is better than one


Gibb"s free energy is positive


Correct answer:

Gibb"s complimentary energy is positive


Explanation:

A galvanic cell outcomes in a hopeful cell potential from a voluntarily reaction. Voluntarily reactions always have a an unfavorable Gibb"s free energy.

An equilibrium constant greater than one would show that the equilibrium concentration of commodities is higher than the equilibrium concentration of reactants, continual with a voluntary reaction.


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Example inquiry #6 : Gibbs totally free Energy and Spontaneity


Consider the following reaction in a galvanic cell:

*
*


What is the Gibb"s complimentary energy for the reaction under typical conditions?

*


Possible Answers:

*


*



*


Correct answer:


Explanation:

You can find the Gibb"s complimentary energy that a galvanic cabinet by utilizing the complying with equation:

*

*
 is the variety of moles of electrons that space transferred in the reaction, 
*
is Faraday"s constant, and 
*
is the potential the the cell.

We are offered the consistent value and the cabinet potential. The mole of electrons transferred is same to the adjust in fee on the atom in the reaction. In this reaction, copper is reduced from a fee of

*
come zero, requiring that is got two mole of electrons.

Using these values, we can find Gibb"s complimentary energy because that the cell.

*

*

Notice the the worth is negative. Galvanic cells are spontaneous, and will have an unfavorable Gibb"s complimentary energies at traditional conditions.

 


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Example inquiry #7 : Gibbs cost-free Energy and Spontaneity


If the reaction quotient (Q) is much less than the equilibrium constant (K), what is true around the Gibbs totally free energy?


Possible Answers:

It is greater than zero


It is equal to zero


We must recognize the reaction enthalpy to recognize the answer


We must recognize the reaction temperature to determine the answer


It is much less than zero


Correct answer:

It is much less than zero


Explanation:

If Q is much less than K, then the reaction has not yet reached the equilibrium state. The will continue spontaneously in the forward direction. Due to the fact that it is proceeding spontaneously in the front direction, this must median that the ΔG (Gibbs cost-free energy) should be negative, or much less than zero.

See more: What Part Of Speech Is The Word Atoll Synonyms, Atoll Antonyms

Enthalpy and also temperature are important when mathematically evaluating Gibbs cost-free energy, however the reaction quotient and also equilibrium constant provide sufficient information come qualitatively determine that the reaction is proceeding spontaneously.


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Example question #8 : Gibbs free Energy and Spontaneity


Of the following reactions, i m sorry of the adhering to is just spontaneous in ~ high enough temperatures?


Possible Answers:

∆H +, ∆S –


∆H +, ∆S +


None of the Above


∆H –, ∆S –


∆H –, ∆S +


Correct answer:

∆H +, ∆S +


Explanation:

Based ~ above Gibbs cost-free Energy, ∆G = ∆H – T∆S, we find that ∆H– will add to spontaneity (∆GReport an Error

Possible Answers:
The reaction is voluntarily
Not enough information come tell
The reaction is nonspontaneous
The reaction is in ~ equilibrium



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Possible Answers:

ΔG → 0 and K → Q


K ⇌ 0


ΔG ← 0 and also K → Q


ΔG ← 0 and also K ← Q


ΔG → 0 and K ← Q





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