Ap Biology Gibbs Free Energy Video Review Sheet

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

Explanation:

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

If the reaction quotient (Q) is greater than the equilibrium abiding (K), what is true about the Gibbs free energy?

Possible Answers:

It is equal to nil.

More than information is needed to determine the gibbs free energy.

Information technology is greater than cipher.

Information technology is less than zero.

Right answer:

Information technology is greater than zero.

Explanation:

If Q is greater than Yard, the reaction has exceeded the equilibrium state. It volition continue nonspontaneously (since equilibrium has already been reached), and this must mean that the ΔG (gibbs costless energy) must be positive, or greater than cypher.

The entropy and enthalpy of a reaction are both negative. Is the reaction spontaneous?

Possible Answers:

The reaction volition be spontaneous if and just if the magnitude of the enthalpy is greater than the magnitude of the entropy times the temperature

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

The reaction will exist spontaneous if and only if the magnitude of the entropy is greater than the magnitude of the enthalpy times the temperature

The reaction is spontaneous

The reaction is not spontaneous

Correct answer:

The reaction will be spontaneous if and only if the magnitude of the enthalpy is greater than the magnitude of the entropy times the temperature

Caption:

A reaction is spontaneous if the Gibb's Free Energy of the reaction is negative.

If , the enthalpy, and , the entropy, are both negative, and then the reaction volition be spontaneous if and but if the magnitude of the enthalpy is greater than the magnitude of the entropy times the temperature.

A system with __________ and__________ will never be spontaneous.

Possible Answers:

positive enthalpy . . . negative entropy

positive enthalpy . . . positive entropy

negative enthalpy . . . positive entropy

negative enthalpy . . . negative entropy

Right answer:

positive enthalpy . . . negative entropy

Caption:

The Gibb's costless energy equation is used to determine the spontaneity of a reaction and is written as follows: .

is Gibb'south gratuitous free energy, is enthalpy, and is entropy. In order for a reaction to be spontaneous, Gibb's energy must accept a negative value. Based on the equation, we can come across that a positive enthalpy in combination with a negative entropy will always upshot in a positive value for Gibb'south free free energy.

This means these are the weather condition that volition always result in a nonspontaneous reaction.

Consider the following reaction in a galvanic cell:

Which if the following statements about the reaction is false?

Possible Answers:

The equilibrium constant is greater than one

The reaction is spontaneous

Gibb's free energy is positive

The jail cell potential is positive

Correct answer:

Gibb'southward free energy is positive

Explanation:

A galvanic cell results in a positive cell potential from a spontaneous reaction. Spontaneous reactions always have a negative Gibb's free energy.

An equilibrium abiding greater than one would indicate that the equilibrium concentration of products is greater than the equilibrium concentration of reactants, consistent with a spontaneous reaction.

Consider the following reaction in a galvanic cell:

What is the Gibb'southward free energy for the reaction under standard conditions?

Correct respond:

Explanation:

You can discover the Gibb's free energy of a galvanic cell by using the following equation:

 is the number of moles of electrons that are transferred in the reaction, is Faraday'south constant, and is the potential of the jail cell.

We are given the constant value and the prison cell potential. The moles of electrons transferred is equal to the alter in charge on the atoms in the reaction. In this reaction, copper is reduced from a charge of to aught, requiring that is gained two moles of electrons.

Using these values, we tin observe Gibb'due south costless energy for the jail cell.

Discover that the value is negative. Galvanic cells are spontaneous, and will have negative Gibb's free energies at standard weather.

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

Possible Answers:

Information technology is less than zero

Information technology is equal to zero

Nosotros must know the reaction temperature to make up one's mind the answer

It is greater than zero

We must know the reaction enthalpy to decide the answer

Correct answer:

Information technology is less than zero

Explanation:

If Q is less than K, then the reaction has not yet reached the equilibrium land. It volition proceed spontaneously in the forward direction. Since it is proceeding spontaneously in the forrard direction, this must mean that the ΔG (Gibbs energy) must exist negative, or less than zero.

Enthalpy and temperature are necessary when mathematically evaluating Gibbs free energy, but the reaction quotient and equilibrium constant provide enough data to qualitatively determine that the reaction is proceeding spontaneously.

Of the following reactions, which of the following is only spontaneous at high enough temperatures?

Possible Answers:

∆H –, ∆S +

∆H +, ∆S –

∆H +, ∆S +

∆H –, ∆S –

None of the Above

Correct answer:

∆H +, ∆S +

Explanation:

Based on Gibbs Gratuitous Energy, ∆G = ∆H – T∆S, nosotros find that ∆H– volition contribute to spontaneity (∆G<0). Since we are looking at temperatures, in order for ∆S to make an nonspontaneous reaction spontaneous at but high temperatures, ∆H will exist positive, and ∆Southward will be positive.

If a reaction has a positive value for its enthalpy and a negative value for its entropy, which of the following is true?

Possible Answers:

The reaction is at equilibrium

The reaction is spontaneous

Not enough data to tell

The reaction is nonspontaneous

Correct answer: The reaction is nonspontaneous

Explanation:

Given the equation for gratuitous energy, (delta)G = (delta)H-T(delta)S, nosotros can determine that the reaction is nonspontaneous at all temperatures if H is positive and South is negative. This combination would always lead to a positive One thousand value, meaning that complimentary energy is required for the reaction to take place and information technology is therefore nonspontaneous.

What must be truthful of a spontaneous process?

Possible Answers:

ΔG → 0 and K → Q

ΔG → 0 and K ← Q

1000 ⇌ 0

ΔG ← 0 and Chiliad → Q

ΔG ← 0 and One thousand ← Q

Correct answer:

ΔG ← 0 and K → Q

Explanation:

Change in free energy must always be negative for a spontaneous process. Additionally, Q must exist less than G and so that the reaction will proceed in the forward reaction, toward equilibrium.

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