Answer:
The ethanol has 21 vibrational modes.
Explanation:
A molecule can show 3 types of motions: one external called translational and two internal called rotational and vibrational. 
In order to calculate the vibrational modes of a molecule we need to know the degrees of freedom of this molecule, it means the number of variables that are involved in the movement of this particle. 
If we know that atoms are three dimensional we will know that they have 3 coordinates expressed as 3N. But the atoms are bonded together so they can move not only in translational but also rotational and vibrational. So, the rotational move can be described in 3 axes and the other vibrational move can be described as 
3N-5 for linear molecules 
3N-6 For nonlinear molecules like ethanol 
So using the formula for nonlinear molecules where N is the amount of atoms in the chemical formula, so ethanol has 9 atoms 
3(9)-6= 21
Thus, ethanol has 21 vibrational modes. 
 
        
             
        
        
        
Explanation:
It is known that equation for ideal gas is as follows.
                PV = nRT
The given data is as follows.
      Pressure, P = 1500 psia,     Temperature, T =  = 104 + 460 = 564 R
 = 104 + 460 = 564 R
      Volume, V = 2.4 cubic ft,      R = 10.73 
Also, we know that number of moles is equal to mass divided by molar mass of the gas.
                 n = 
             m = 
                 =  
 
                 = 9.54 lb
Hence, molecular weight of the gas is 9.54 lb.
- We will calculate the density as follows.
                 d = 
                     =  
 
                     = 3.975 
- Now, calculate the specific gravity of the gas as follows.
   Specific gravity relative to air =  
                          = 
                          = 51.96 
 
        
             
        
        
        
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Answer is: adding NaCl will lower the freezing point of a solution.
A solution (in this example solution of sodium chloride) freezes at a lower temperature than does the pure solvent (deionized water). 
The higher the solute concentration (sodium chloride), freezing point depression of the solution will be greater.
Equation describing the change in freezing point:  
ΔT = Kf · b · i.
ΔT - temperature change from pure solvent to solution.
Kf - the molal freezing point depression constant.
b -  molality (moles of solute per kilogram of solvent).
i - Van’t Hoff Factor.
Dissociation of sodium chloride in water: NaCl(aq) →  Na⁺(aq) + Cl⁻(aq).