Question

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 Δ*H* and Δ*S* do not change with
temperature.

**Part C**

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

Answer #1

A)

ΔH = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

T = 298 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1204.0 - 298.0 * -0.2171

ΔG = -1139.3042 KJ

Answer: -1139 KJ

b)

Now we have:

ΔH = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

T = 5958 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1204.0 - 5958.0 * -0.2171

ΔG = 89.5 KJ

Answer: 89.5 KJ

c)

Now we have:

ΔH = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

ΔG = 0 for equilibrium process

use:

ΔG = ΔH - T*ΔS

0.0 = -1204.0 - T *-0.2171

T = 5545.8314 K

Answer: 5546 K

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...

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...

± 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...

PART 1. Which of the following reactions are spontaneous
(favorable). Check all that apply.
A. 2Mg(s)+O2(g)--->2MgO(s) delta G=-1137kj/mol
B.NH3(g)+HCl(g)--->NH4Cl(s) delta G=-91.1 kj/mol
C.AgCl(s)--->Ag+(aq)+Cl-(aq) delta G=55.6 kj/mol
D.2H2(g)+O2(g)--->2H2O(g) delta G=456 kj/mol
E.C(s)+H2O(l)--->CO(g)+H2(g) delta G=90.8 kj/mol
F.CH4(g)+2O2(g)--->CO2(g)+2H2O(l) delta G=-820
kj/mol
PART 2. Calculate the
standard entropy, ΔS°rxn, of the following reaction at 25.0 °C
using the data in this table. The standard enthalpy of the
reaction, ΔH°rxn, is –633.1 kJ·mol–1.
3C2H2(g)--->C6H6(l) ΔS°rxn=____JxK-1xmol-1
Then calculate Gibbs free energy for ΔG°rxn in kjxmol-1
Finally,...

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?

2Mg(s) + O2(g) → 2MgO(s) ΔHrxn = -1204 kJ
Assume the heat given off from this reaction is used to heat a
block of iron. Specific heat capacity of iron = 0.44 J g C
What mass of Mg must react with excess oxygen in order to warm a
2.60 kg block of iron from 20.0 C to 60.0 C?

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...

For a given reaction, ΔH = -26.6 kJ/mol and ΔS = -77.0 J/K⋅mol.
The reaction is spontaneous ________. Assume that ΔH and ΔS do not
vary with temperature.
For a given reaction, = -26.6 kJ/mol and =
-77.0 J/Kmol. The reaction is spontaneous ________. Assume
that and do not vary with temperature.
at T > 298 K
at all temperatures
at T < 345 K
at T < 298 K
at T > 345 K

Consider the following reaction: 2NO(g)+O2(g)→2NO2(g) Estimate
ΔG∘ for this reaction at each of the following temperatures and
predict whether or not the reaction will be spontaneous. (Assume
that ΔH∘ and ΔS∘ do not change too much within the give temperature
range.)
a. 298 K
b. 721 K
c. 853 K

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