- #1
sgstudent
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Hi I have a couple of questions relating to these topic hope you guys can help :)
Comparing ethanol and water, ethanol has weaker intermolecular forces than water. However, it has a greater specific heat capacity by kJ/mol.K than water. Meaning more energy would have to be absorbed per mole of ethanol to raise the temperature by 1K than for water.
1)I read that having a greater degree of freedom would mean the specific heat capacity is greater but I don't quite understand why this is so. Can someone explain this? cos I can't seem to find an explanation for this. I would think that the reason for that is that when ethanol gains 1J of energy, it is distributed to translational, rotational and vibrational kinetic energy as well as potential energy. So when we compare per mole of ethanol and water, a larger portion of that 1J goes to the translational energy component causing it to have a greater increase in temperature in water than in ethanol?
2)However reading this link "http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html#c2" they said that the total KE of 1gram of copper is the same for 1gram in water. However I don't quite understand this. Since total KE is the average KE multiplied by the number of molecules. In 1g of water and 1g of copper there are different numbers of molecules. So at the same temperature, the total KE shouldn't be the same right?
3)However, how would the specific heat capacity correlate to molecular bond strength too? Or is there no link in the 2 concepts besides that once it reaches a certain amount of kinetic energy, then it would have enough energy to vapourize? So enthapy of vaporization is greater for water than for ethanol.
4)Then again, the ethanol boils at a lower temperature than water. So it would have to have a greater vapour pressure at any given temperature - meaning more ethanol evaporates at a given temperature than water. So would we explain that because the enthalpy of vaporization is less for water than ethanol due to the weaker intermolecular forces so more ethanol would evaporate at a given temperature?
But I'm not quite sure about that. Because even though the enthalpy of vaporization is greater for water than ethanol, due to the higher molar heat capacity I'm not too sure why it would evaporate at faster rate actually. I'm thinking these 2 factors contradict each other somehow. Where would my misconception be?
Sorry for the long post. Hope you guys can help :)
Comparing ethanol and water, ethanol has weaker intermolecular forces than water. However, it has a greater specific heat capacity by kJ/mol.K than water. Meaning more energy would have to be absorbed per mole of ethanol to raise the temperature by 1K than for water.
1)I read that having a greater degree of freedom would mean the specific heat capacity is greater but I don't quite understand why this is so. Can someone explain this? cos I can't seem to find an explanation for this. I would think that the reason for that is that when ethanol gains 1J of energy, it is distributed to translational, rotational and vibrational kinetic energy as well as potential energy. So when we compare per mole of ethanol and water, a larger portion of that 1J goes to the translational energy component causing it to have a greater increase in temperature in water than in ethanol?
2)However reading this link "http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html#c2" they said that the total KE of 1gram of copper is the same for 1gram in water. However I don't quite understand this. Since total KE is the average KE multiplied by the number of molecules. In 1g of water and 1g of copper there are different numbers of molecules. So at the same temperature, the total KE shouldn't be the same right?
3)However, how would the specific heat capacity correlate to molecular bond strength too? Or is there no link in the 2 concepts besides that once it reaches a certain amount of kinetic energy, then it would have enough energy to vapourize? So enthapy of vaporization is greater for water than for ethanol.
4)Then again, the ethanol boils at a lower temperature than water. So it would have to have a greater vapour pressure at any given temperature - meaning more ethanol evaporates at a given temperature than water. So would we explain that because the enthalpy of vaporization is less for water than ethanol due to the weaker intermolecular forces so more ethanol would evaporate at a given temperature?
But I'm not quite sure about that. Because even though the enthalpy of vaporization is greater for water than ethanol, due to the higher molar heat capacity I'm not too sure why it would evaporate at faster rate actually. I'm thinking these 2 factors contradict each other somehow. Where would my misconception be?
Sorry for the long post. Hope you guys can help :)
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