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User:Mg5715

From ChemWiki

NH3, N2, H2 and ClF were looked at in this wiki page and Gaussian was used to optimise and analyse those four molecules. GaussView 5.0 will give summary of the molecule including the energy of molecule. Based on the molecular energy,the reaction energy of the Haber process was calculated. Comparing with the literature value, we know that the value calculated by computer is different from the literature value.

NH3 molecule

The optimisation file of NH3 is linked here

Information

basic information of NH3
Parameter data
Molecule name NH3
Calculation method RB3LYP
Basis set 6-31G(d.p)
Final energy E(RB3LYP) -56.55776810 a.u.
RMS Gradient Norm 0.00025207 a.u.
point group C3V


         Item               Value     Threshold  Converged?
 Maximum Force            0.000419     0.000450     YES
 RMS     Force            0.000274     0.000300     YES
 Maximum Displacement     0.000894     0.001800     YES
 RMS     Displacement     0.000551     0.001200     YES                           
NH3 molecule

Vibration

Vibration of NH3.

Qustions

1.how many modes do you expect from the 3N-6 rule?

3*4-6=6

2.which modes are degenerate (ie have the same energy)?

mode 2 with mode 3& mode 5 with mode 6

3.which modes are "bending" vibrations and which are "bond stretch" vibrations?

bending: mode 1, mode 2, and mode 3

stretching: mode 4, mode 5, and mode 6

4.which mode is highly symmetric?

mode 4

5.one mode is known as the "umbrella" mode, which one is this?

mode 1

6.how many bands would you expect to see in an experimental spectrum of gaseous ammonia?

2. Only if the dipole moment changes while vibrating, it will give a band in spectrum. Mode 4,5,and 6 give small changes in dipole moment, so the intensities are small and will not give bands in the spectrum.


Charge Analysis

Charge anaylsis of NH3.

charge on N=-1.125

charge on H=+0.375

Because the overall charge on NH3 should be zero and the electronegativity of N is greater, N will have negative charge and H will have positive charge.


N2 molecule

The optimisation file of N2 is linked here

Information

basic information of N2
Parameter data
Molecule name N2
Calculation method RB3LYP
Basis set 6-31G(d.p)
Final energy E(RB3LYP) -109.52412868 a.u.
RMS Gradient Norm 0.00000060 a.u.
point group D∞H


         Item               Value     Threshold  Converged?
 Maximum Force            0.000001     0.000450     YES
 RMS     Force            0.000001     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000000     0.001200     YES
N2 molecule

Vibration

Vibration of N2.

There is only one vibration mode in N2 and it will not give any band in spectrum because the dipole moment does not change.

Charge Analysis

Charge anaylsis of N2.

charge on N=0

That is because there in no electronegativity differences between two N atoms. Hence electrons are shared equally between the two N atoms.

H2 molecule

The optimisation file of H2 is linked here

Information

basic information of H2
Parameter data
Molecule name H2
Calculation method RB3LYP
Basis set 6-31G(d.p)
Final energy E(RB3LYP) -1.17853936 a.u.
RMS Gradient Norm 0.00000017 a.u.
point group D∞H


         Item               Value     Threshold  Converged?
 Maximum Force            0.000000     0.000450     YES
 RMS     Force            0.000000     0.000300     YES
 Maximum Displacement     0.000000     0.001800     YES
 RMS     Displacement     0.000001     0.001200     YES
H2 molecule

Vibration

Vibration of H2.

There is only one vibration mode in H2 and it will not give any band in spectrum because the dipole moment does not change.

Charge Analysis

Charge anaylsis of H2.

charge on H=0

That is because there in no electronegativity differences between two H atoms. Hence electrons are shared equally between the two H atoms.

Haber-Bosch process

E(NH3)=-56.55776810 a.u.

2*E(NH3)=-113.1155362 a.u.

E(N2)=-109.52412868 a.u.

E(H2)=-1.17853936 a.u.

3*E(H2)=-3.53561808 a.u.

ΔE=2*E(NH3)-[E(N2)+3*E(H2)]=-0.05578944 a.u.=-146.8143158 kJ/mol

Haber-Bosch process is exothermic and this indicates energy level of NH3 is lower than the engery level of N2 and H2.

Literature value=-92.4 kJ/mol[1]

The value calculated by the computer is not same as the literature value which shows that the computer is biased.

ClF molecule

The optimisation file of ClF is linked here

Information

basic information of H2
Parameter data
Molecule name ClF
Calculation Type FREQ
Calculation method RB3LYP
Basis set 6-31G(d.p)
Final energy E(RB3LYP) -559.94269584 a.u.
RMS Gradient Norm 0.00009730 a.u.
Dipole Moment 0.9773 Debye
point group C∞V


         Item               Value     Threshold  Converged?
 Maximum Force            0.000169     0.000450     YES
 RMS     Force            0.000169     0.000300     YES
 Maximum Displacement     0.000295     0.001800     YES
 RMS     Displacement     0.000418     0.001200     YES
ClF molecule

Vibration

Vibration of ClF.

Only one brand is showed in the spectrum because it is diatomic molecule and it will give one vibration mode. When the molecule is vibrating, the dipole moment of this molecule is changed because of difference in electronegativities.

Charge Analysis

Charge anaylsis of ClF.

charge on Cl= +0.309

Charge on F= -0.309

Because the electronegativity of F is greater than that of Cl, the charge on F is negative.

MO Analysis

1. 2p-3p πg antibonding orbital

HOMO of ClF.

component: 2py of F and 3py of Cl

Energy: -0.32847 a.u.

This molecular orbital is the HOMO (highest occupied molecular orbital)

The 3p orbital of Cl has higher energy level and it is much closer to the energy level of anti-bonding orbital so Cl will have more contribution to the anti- bonding orbital. The bonding π orbital is showed in 3.

2. 2p-3p σu anti-bonding orbital

LUMO of ClF.

component: 2px of F and 3px of Cl

Energy: -0.12121 a.u.

This molecular orbital is the LUMO (lowest unoccupied molecular orbital)

The 3p orbital of Cl has higher energy level and it is much closer to the energy level of anti-bonding orbital so Cl will have more contribution to the anti- bonding orbital. The bonding σ orbital is showed in 4.

When electron is added in the LUMO, the bond of F and Cl becomes weaker.

3. 2p-3p πu bonding orbital

2p-3p πu bonding orbital of ClF.

component: 2py of F and 3py of Cl

Energy: -0.46728 a.u.

The 2p orbital of F has lower energy level and it is much closer to the energy level of bonding orbital so F has more contribution to the bonding orbital. The anti-bonding orbital is showed in 1.

4. 2p-3p σg bonding orbital

2p-3p σg bonding orbital of ClF.

component: 2px of F and 3px of Cl

Energy: -0.52326 a.u.

The 2p orbital of F has lower energy level and it is much closer to the energy level of bonding orbital so F has more contribution to the bonding orbital. The anti-bonding orbital is showed in 2.

5. 2s-3s σg bonding orbital

2s-3s σg bonding orbital of ClF.

component: 2s of F and 3s of Cl

Energy: -1.21890 a.u.

The 2s orbital of F has lower energy level and it is much closer to the energy level of bonding orbital so F has more contribution to the bonding orbital.