Question

± Gibbs Free Energy: Temperature Dependence Gibbs free energy (G) is a measure of the spontaneity of a chemical reaction. It is the chemical potential for a reaction, and is minimized at equilibrium. It is defined as G=H−TS where H is enthalpy, T is temperature, and S is entropy.

The chemical reaction that causes aluminum to corrode in air is given by

4Al+3O2→2Al2O3

in which at 298 K

ΔH∘rxn |
= −3352 kJ |

ΔS∘rxn |
= −625.1 J/K |

**Part A**

What is the standard Gibbs free energy for this reaction? Assume the commonly used standard reference temperature of 298 K.

Express your answer as an integer and include the appropriate units.

**Part B**

What is the Gibbs free energy for this reaction at 5975 K ?
Assume that Δ*H* and Δ*S* do not change with
temperature.

Express your answer to two decimal places and include the appropriate units.

**Part C**

At what temperature *T*eq do the forward and reverse
corrosion reactions occur in equilibrium?

Express your answer as an integer and include the appropriate units.

Answer #1

**A)**

**we know that**

**dGo = dHo - TdSo**

**so**

**dGo = (-3352 x 1000) - ( 298 x -625.1)**

**dGo = -3165.72**

**so**

**standard gibbs free energy is -3165.72 kJ**

**B)**

**now**

**dG = dH - TdS**

**given**

**dH and dS do not change**

**and**

**T = 5975 K**

**so**

**dG = ( -3352 x 1000) - ( 5975 x -625.1)**

**dG = 382.9725 kJ**

**so**

**at 5975 K**

**gibbs free energy for this reactioon is 382.9725
kJ**

**C)**

**we know that**

**at equilibrium**

**dG= 0**

**so**

**dH - TdS= 0**

**dH = TdS**

**T = dH / dS**

**so**

**T = -3352 x 1000 / -625.1**

**T = 5362.34**

**so**

**at 5362.34 K , it will be at equilibrium**

The chemical reaction that causes magnesium to corrode in air is
given by 2Mg+O2→2MgO in which at 298 K ΔH∘rxn = −1204 kJ ΔS∘rxn =
−217.1 J/K
Part A What is the standard Gibbs free energy for this reaction?
Assume the commonly used standard reference temperature of 298 K.
Express your answer as an integer and include the appropriate
units.
Part B
What is the Gibbs free energy for this reaction at 5958 K ?
Assume that ΔH and ΔS...

The chemical reaction that causes iron to corrode in air is
given by
4Fe+3O2→2Fe2O3
in which at 298 K
ΔH∘rxn
= −1684 kJ
ΔS∘rxn
= −543.7 J/K
Part A:
What is the standard Gibbs free energy for this reaction? Assume
the commonly used standard reference temperature of 298 K.
Part B:
What is the Gibbs free energy for this reaction at 3652 K ?
Assume that ΔH and ΔS do not change with
temperature.
Part C:
At what temperature Teq...

The chemical reaction that causes iron to corrode in air is
given by
4Fe+3O2→2Fe2O3
in which at 298 K
ΔH∘rxn
= −1684 kJ
ΔS∘rxn
= −543.7 J/K
Gibbs free energy (G) is a measure of the spontaneity of a
chemical reaction. It is the chemical potential for a reaction, and
is minimized at equilibrium. It is defined as G=H−TS where H is
enthalpy, T is temperature, and S is entropy.
Part A
What is the standard Gibbs free energy for...

Calculate the change in Gibbs free energy for each of the
following sets of ΔHrxn ∘, ΔS∘rxn, and
T.
1) ΔH∘rxn=− 97 kJ , ΔS∘rxn=− 154 J/K ,
T= 310 K
Express your answer using two significant figures.
2) ΔH∘rxn=− 97 kJ , ΔS∘rxn=− 154 J/K ,
T= 856 K
3) ΔH∘rxn= 97 kJ , ΔS∘rxn=− 154 J/K ,
T= 310 K
4) ΔH∘rxn=− 97 kJ , ΔS∘rxn= 154 J/K ,
T= 408 K

� Gibbs Free Energy: Equilibrium Constant
Nitric oxide, NO, also known as nitrogen monoxide, is one of the
primary contributors to air pollution, acid rain, and the depletion
of the ozone layer. The reaction of oxygen and nitrogen to form
nitric oxide in an automobile engine is
N2(g)+O2(g)?2NO(g)
The spontaneity of a reaction can be determined from the free
energy change for the reaction, ?G?.
A reaction is spontaneous when the free energy change is less
than zero.
A reaction...

The chemical reaction that causes iron to corrode in air is
given by 4Fe(s)+3O2(g)→2Fe2O3(s)
and
ΔrH∘ = −1684 kJ mol−1
ΔrS∘ = −543.7 J K−1 mol−1
a) What is the standard Gibbs energy change for this reaction?
Assume the commonly used standard reference temperature of 298
K.
b) What is the Gibbs energy for this reaction at 3652 K ? Assume
that ΔrH∘ and ΔrS∘ do not change with
temperature.
c) The standard Gibbs energy change, ΔrG∘, applies only
when...

he thermodynamic properties for a reaction are related by the
equation that defines the standard free energy, ΔG∘, in
kJ/mol:
ΔG∘=ΔH∘−TΔS∘
where ΔH∘ is the standard enthalpy change in kJ/mol and
ΔS∘ is the standard entropy change in J/(mol⋅K). A good
approximation of the free energy change at other temperatures,
ΔGT, can also be obtained by utilizing this
equation and assuming enthalpy (ΔH∘) and entropy
(ΔS∘) change little with temperature.
Part A
For the reaction of oxygen and nitrogen to...

Calculate the change in Gibbs free energy for each of the
following sets of ?H?rxn, ?S?rxn, and T.
Part A ?H?rxn=? 115 kJ ; ?S?rxn= 248 J/K ; T= 295 K
Part B ?H?rxn= 115 kJ ; ?S?rxn=? 248 J/K ; T= 295 K
Part C ?H?rxn=? 115 kJ ; ?S?rxn=? 248 J/K ; T= 295 K Express
your answer using two significant figures.
Part D ?H?rxn=? 115 kJ ; ?S?rxn=? 248 J/K ; T= 565 K Express
your answer...

A. Using given data, calculate the change in
Gibbs free energy for each of the following reactions. In each case
indicate whether the reaction is spontaneous at 298K under standard
conditions.
2H2O2(l)→2H2O(l)+O2(g)
Gibbs free energy for H2O2(l) is -120.4kJ/mol
Gibbs free energy for H2O(l) is -237.13kJ/mol
B. A certain reaction has ΔH∘ = + 35.4
kJ and ΔS∘ = 85.0 J/K . Calculate ΔG∘ for the
reaction at 298 K. Is the reaction spontaneous at
298K under standard
conditions?

Assume we know the Gibbs free energy of reaction for a chemical
reaction taking place at 298 K. What additional
thermodynamic information do we need to know to compute
the equilibrium constant of the reaction (a) at 298 K and (b) at
350 K? (You may assume that no phase transitions take place in this
temperature range.)

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