Why Does Heat Generate When Mixing Ethanol and Water?

[nirmaljoshi]

Why heat is generated when ethanol is mixed with water? Please also explain why the existing hydrogen bond of water disintegrated to accommodate ethanol molecule?

 

[sagarbhathwar]

Ethanol molecules are much smaller in size than the water molecules and as a consequence some of the ethanol molecules tend to cram in between the water molecules, thus breaking the hydrogen bond.
Enthalpy of mixing water and ethanol is -ve(exothermic), hence heat is liberated.

 

[Orodruin]

Ethanol molecules are much smaller in size than the water molecules and as a consequence some of the ethanol molecules tend to cram in between the water molecules, thus breaking the hydrogen bond.

Water molecules are significantly smaller than ethanol molecules.

Water: H2O
Ethanol: CH3-CH2-OH

 

[sagarbhathwar]

Oh I am extremely sorry. It exactly the other way around. Swap places with ethanol and water :)

Thanks
Sagar

 

[nirmaljoshi]

Enthalpy of mixing water and ethanol is -ve(exothermic), hence heat is liberated.

My question is why it is exothermic? As you said, "Ethanol molecules are much smaller in size than the water molecules and as a consequence some of the ethanol molecules tend to cram in between the water molecules, thus breaking the hydrogen bond."

But after mixing, water and ethanol again forms the hydrogen bond and hence they remain in stable form. That is, one hydrogen bond is broken and another is formed. If so, there should not be any liberation of energy.

Please correct me if i am on wrong way.

 

[sagarbhathwar]

Yes. H-bond is formed again between hydrogen and water molecules but the strength of this bond is weaker than that between water-water molecules. So I am guessing that is why some heat is liberated.
Always consider difference in strength of the bonds. Not just the bonds.

 

[nirmaljoshi]

Thanks.

Could you please briefly direct me how the difference in strength of bond is measured?