Bond energy between two water molecules

AI Thread Summary
To estimate the bond energy between two water molecules, the average distance between molecules must first be calculated using the density of water (1000 kg/m^3) and the molecular weight of H2O (18 g/mol). The calculation involves determining the volume of a single water molecule, which can be derived from the molar mass and Avogadro's number. The discussion highlights a common confusion regarding the correct units for molar mass, clarifying that it should be expressed as 18 g/mol or 18 x 10^-3 kg/mol. Additionally, participants seek guidance on how to proceed with the calculations without directly asking for answers. Understanding these foundational concepts is crucial for further analysis of water's surface tension and energy.
FaraDazed
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Homework Statement



Estimate the bond energy between two water molcules (liquid) in the following way

A: From the density of water and its molecular weight calculate the average distance between the molecules

B:hence show that there are 10^19 molcules per m^2 of surace

C:from the suraface tension of water, assuming this to be the same as the suraface energy, fine the value of U_0

Homework Equations



N_s ≈ \frac{1}{r_0^2} \\<br /> \frac{1}{4}nU_0N_s \\<br /> \gamma = \frac{F}{L} \\<br />

The Attempt at a Solution



I am stuck straight away on part A. I know the density of water (1000 kg/m^3) and the molecular weight of H2O is 18 but have no idea how these are supposed to help me calculate the average distance between the molecules.

I am not looking for the answer but any hints on where to start would be very much appreciated.
 
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The volume of one molecule (in m^3):
$$
V_1 = \frac {μ}{ρ N_A}
$$
where ## μ = 18×10^3 kg/mole##
## ρ = 10^3 kg/m^3##
## N_A = 6×10^{23} mole^{-1}##
 
GregoryS said:
The volume of one molecule (in m^3):
$$
V_1 = \frac {μ}{ρ N_A}
$$
where ## μ = 18×10^3 kg/mole##
## ρ = 10^3 kg/m^3##
## N_A = 6×10^{23} mole^{-1}##

OK Thank you, what is mu called? (For example rho is density)
 
FaraDazed said:
OK Thank you, what is mu called? (For example rho is density)
I think it's supposed to be the molar mass of water (2xH+1xO = 18). But I believe it should be 18g/mol, the molar unit having been defined in terms of grammes before the old cgs units were replaced by MKS units. So that's 18 10-3 kg/mol, not 18 10+3 kg/mol.
 
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