Jump to content

Rep:Mod:hz1995

From ChemWiki

I investigated the energetics of the Haber process. To do this, I optimised the molecules NH3, N2 and H2 using GaussView 5.0. I then extracted the molecular information, including charge, bond length and vibration properties, and looked at the dynamic images for all three. Having worked out the energetics, I applied a similar method to a molecule of my choice, Cl2. In addition to the molecular information, I also analysed the Molecular orbitals and the relevant Atomic orbitals responsible for these MOs.


Ammonia Molecule

Summary 

File Name:	Haaris - optimised NH3

File Type:	.log

Calculation Type:	FREQ

Calculation Method:	RB3LYP

Basis Set:	6-31G(d,p)

Charge:	0

Spin:	Singlet

E(RB3LYP):	-56.55776873	 a.u.

RMS Gradient Norm:	0.00000485	 a.u.

Imaginary Freq:	0

Dipole Moment:	1.8466	 Debye
Point Group:	C3V

         Item               Value     Threshold  Converged?
 Maximum Force            0.000004     0.000450     YES
 RMS     Force            0.000004     0.000300     YES
 Maximum Displacement     0.000072     0.001800     YES
 RMS     Displacement     0.000035     0.001200     YES
 Predicted change in Energy=-5.986278D-10
 Optimization completed.
    -- Stationary point found.
                           ----------------------------
                           !   Optimized Parameters   !
                           ! (Angstroms and Degrees)  !
 --------------------------                            --------------------------
 ! Name  Definition              Value          Derivative Info.                !
 --------------------------------------------------------------------------------
 ! R1    R(1,2)                  1.018          -DE/DX =    0.0                 !
 ! R2    R(1,3)                  1.018          -DE/DX =    0.0                 !
 ! R3    R(1,4)                  1.018          -DE/DX =    0.0                 !
 ! A1    A(2,1,3)              105.7412         -DE/DX =    0.0                 !
 ! A2    A(2,1,4)              105.7412         -DE/DX =    0.0                 !
 ! A3    A(3,1,4)              105.7412         -DE/DX =    0.0                 !
 ! D1    D(2,1,4,3)           -111.8571         -DE/DX =    0.0                 !
 --------------------------------------------------------------------------------
 GradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGrad

Optimisation graph

Dynamic Image

Optimised NH3 molecule

Link to completed optimisation file File:HAARIS - OPTIMISED NH3.LOG

Vibration properties

How many modes do you expect from the 3N-6 rule? - (3x4)-6 = 6 modes.

Which modes are degenerate (ie have the same energy)? - Modes 2 and 3 (Freq 1693.95), and 5 and 6 (Freq 3589.82).

Which modes are "bending" vibrations and which are "bond stretch" vibrations? - Bending 1,2,3 and stretching 4,5,6.

Which mode is highly symmetric? - 4

One mode is known as the "umbrella" mode, which one is this? - 1

How many bands would you expect to see in an experimental spectrum of gaseous ammonia? - There are two distinct frequencies for the 6 modes therefore you would expect 2 bands. Two frequencies have a very small value on the y-axis (relative intensity) which would make them difficult to see. They have small intensities because the change in dipole moment is small.

Charge distribution

You would expect Nitrogen to be negatively charged and Hydrogen to be positively charged since Nitrogen is more electronegative and will therefore attract bonding electrons towards itself.

Hydrogen Molecule

Summary 


File Name:	H2

File Type:	.log

Calculation Type:	FREQ

Calculation Method:	RB3LYP

Basis Set:	6-31G(d,p)

Charge:	0

Spin:	Singlet

E(RB3LYP):	-1.17853936	 a.u.

RMS Gradient Norm:	0.00000017	 a.u.

Imaginary Freq:	0

Dipole Moment:	0.0000	 Debye

Point Group:	D*H

Bond Length: 0.74279 A




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
 Predicted change in Energy=-1.164079D-13
 Optimization completed.
    -- Stationary point found.
                           ----------------------------
                           !   Optimized Parameters   !
                           ! (Angstroms and Degrees)  !
 --------------------------                            --------------------------
 ! Name  Definition              Value          Derivative Info.                !
 --------------------------------------------------------------------------------
 ! R1    R(1,2)                  0.7428         -DE/DX =    0.0                 !
 --------------------------------------------------------------------------------
 GradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGrad

Dynamic image

Optimised H2 molecule

Link to completed optimisation file - File:HZ H2.LOG

Vibration properties

Nitrogen Molecule

Summary 


File Name:	HZ_n2_optimised

File Type:	.log

Calculation Type:	FREQ

Calculation Method:	RB3LYP

Basis Set:	6-31G(d,p)

Charge:	0

Spin:	Singlet

E(RB3LYP):	-109.52412868	 a.u.

RMS Gradient Norm:	0.00000060	 a.u.

Imaginary Freq:	0

Dipole Moment:	0.0000	 Debye

Point Group:	D*H

Bond length: 1.10550 A



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
 Predicted change in Energy=-3.383811D-13
 Optimization completed.
    -- Stationary point found.
                           ----------------------------
                           !   Optimized Parameters   !
                           ! (Angstroms and Degrees)  !
 --------------------------                            --------------------------
 ! Name  Definition              Value          Derivative Info.                !
 --------------------------------------------------------------------------------
 ! R1    R(1,2)                  1.1055         -DE/DX =    0.0                 !
 --------------------------------------------------------------------------------
 GradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGrad

Dynamic image

Optimised N2 Molecule

Link to completed optimisation file - File:HZ N2 OPTIMISED.LOG

Vibration properties

Haber-Bosch Reaction Energy

Calculations

N2 + 3h2--> 2NH3

E(NH3)= -56.55776873 a.u.

2*E(NH3)= -56.55776873 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)]= -0.05579074 a.u.

ΔE= -0.05579074 x 2625.5 = -146.4785879 kJ/mol.

The negative energy value shows that energy is released. This indicates that Ammmonia more stable than the mixture of H2 and N2.

Cl2

Summary 


File Name:	hz_cl2_optimised

File Type:	.log

Calculation Type:	FREQ

Calculation Method:	RB3LYP

Basis Set:	6-31G(d,p)

Charge:	0

Spin:	Singlet

E(RB3LYP):	-920.34987886	 a.u.

RMS Gradient Norm:	0.00002511	 a.u.

Imaginary Freq:	0

Dipole Moment:	0.0000	 Debye

Point Group:	D*H




         Item               Value     Threshold  Converged?
 Maximum Force            0.000043     0.000450     YES
 RMS     Force            0.000043     0.000300     YES
 Maximum Displacement     0.000121     0.001800     YES
 RMS     Displacement     0.000172     0.001200     YES
 Predicted change in Energy=-5.277357D-09
 Optimization completed.
    -- Stationary point found.
                           ----------------------------
                           !   Optimized Parameters   !
                           ! (Angstroms and Degrees)  !
 --------------------------                            --------------------------
 ! Name  Definition              Value          Derivative Info.                !
 --------------------------------------------------------------------------------
 ! R1    R(1,2)                  2.0417         -DE/DX =    0.0                 !
 --------------------------------------------------------------------------------
 GradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGrad

Dynamic image

Optimised Cl2 Molecule

Link to optimised file - File:HZ CL2 OPTIMISED.LOG

Vibration properties


Cl2 Molecular Orbitals

2s σ* Anti-bonding MO

2s σ Bonding MO formed by overlap of 2s orbitals

2pz σ Bonding MO formed by overlap of 2pz orbitals

2px Pi Anti-bonding MO

Since both Chlorine atoms have the same electronegativity, the electrostatic potential of the surface is symmetrical.

Retrieved from "https://chemwiki.ch.ic.ac.uk/index.php?title=Rep:Mod:hz1995&oldid=819522"