If rotational constant for H2O(g) at 15000K are A = 27.8778cm-1, B = 1...
The change in rotational free energy (ΔG_rot) can be calculated using the formula:
ΔG_rot = -RTln(Q_rot)
where R is the gas constant, T is the temperature in Kelvin, and Q_rot is the partition function for rotational motion.
To calculate Q_rot, we need to use the rotational constants A, B, and C for H2O(g) at 15000K.
The partition function for rotational motion can be calculated as follows:
Q_rot = (8π^2IkT) / (h^2cA) × (8π^2IkT) / (h^2cB) × (8π^2IkT) / (h^2cC)
where I is the moment of inertia of the molecule, k is Boltzmann's constant, h is Planck's constant, and c is the speed of light.
To calculate the moment of inertia, we can use the formula:
I = μr^2
where μ is the reduced mass of the molecule and r is the bond length.
For H2O, the bond length (r) is approximately 0.96 Å and the reduced mass (μ) can be calculated as:
μ = (mH * mO) / (mH + mO)
where mH is the mass of hydrogen and mO is the mass of oxygen.
Substituting the values into the equation, we can calculate the reduced mass:
μ = (2 * 16.00 amu) / (2 + 16.00 amu) = 2.67 amu
Next, we can calculate the partition function:
Q_rot = (8π^2 * 2.67 amu * 1.38 J/K * 15000 K) / (6.63 x 10^-34 J·s)^2 * (2.998 x 10^8 m/s) * 27.8778 cm^-1) × (8π^2 * 2.67 amu * 1.38 J/K * 15000 K) / (6.63 x 10^-34 J·s)^2 * (2.998 x 10^8 m/s) * 14.5042 cm^-1) × (8π^2 * 2.67 amu * 1.38 J/K * 15000 K) / (6.63 x 10^-34 J·s)^2 * (2.998 x 10^8 m/s) * 9.286 cm^-1)
Calculating the value, we get:
Q_rot ≈ 1.59 x 10^49
Finally, we can substitute the values into the equation for ΔG_rot:
ΔG_rot = -RTln(Q_rot)
Substituting the values:
ΔG_rot = -(8.314 J/(mol·K))(15000 K) ln(1.59 x 10^49)
Calculating the natural logarithm and the negative sign, we get:
ΔG_rot ≈ -(-77.18 kJ/mol) ≈ 77.18 kJ/mol
Therefore, the value of ΔG_rot is approximately -77.18 kJ/mol.