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bananenheld
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What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

According to this reference: http://khimiya.org/volume15/Entropia.pdf the meaning of standard molar entropy is the relative amount of energy that the substance must have to exist at for example 298 Kelvin.

An example is given of diamond and graphite, which has 2.4 J/K and 5.7 J/K respectively. I see that graphite has less strong bonds than diamond, i.e. diamond has higher potential energy stored inside its bonds. But I don't understand how that translates into a lower amount of energy needed to exist at a certain temperature? Is this the energy that needs to be supplied to the diamoned to raise its temperature to 298 kelvin? But isn't it than just a kind of heat capacity? What happens if you did not transfer enough energy to make it exist stably at that temperature?

  1. The meaning of standard molar entropy values When seen in their relation to the energy content of a substance, standard molar entropy values, $S^0_{298}$, give useful insight that is absent when - as is usual - those J/K values are treated as merely abstract numbers to be added or subtracted in determining a $dS_0$ reaction . A $S^0_{298}$ value for a substance is the number of joules of energy/T transferred incrementally (reversibly, from the surroundings at each T) to a mole of substance from 0 K to 298 K. Thus, this number is a rough indicator or approximate index (not the joules dispersed at 298 K, nor the total joules dispersed from 0 K to 298 K!) of the relative amount of energy that the substance must have to be exist stably at 298 K. This is why $S^0_{298}$ values illuminate e.g., the difference in rigidity of bonding: the more rigid bonds of diamond (2.4 J/K) vs. the looser interatomic bonds in graphite (5.7 J/K) ,

What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

According to this reference: http://khimiya.org/volume15/Entropia.pdf the meaning of standard molar entropy is the relative amount of energy that the substance must have to exist at for example 298 Kelvin.

An example is given of diamond and graphite, which has 2.4 J/K and 5.7 J/K respectively. I see that graphite has less strong bonds than diamond, i.e. diamond has higher potential energy stored inside its bonds. But I don't understand how that translates into a lower amount of energy needed to exist at a certain temperature? Is this the energy that needs to be supplied to the diamoned to raise its temperature to 298 kelvin? But isn't it than just a kind of heat capacity? What happens if you did not transfer enough energy to make it exist stably at that temperature?

What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

According to this reference: http://khimiya.org/volume15/Entropia.pdf the meaning of standard molar entropy is the relative amount of energy that the substance must have to exist at for example 298 Kelvin.

An example is given of diamond and graphite, which has 2.4 J/K and 5.7 J/K respectively. I see that graphite has less strong bonds than diamond, i.e. diamond has higher potential energy stored inside its bonds. But I don't understand how that translates into a lower amount of energy needed to exist at a certain temperature? Is this the energy that needs to be supplied to the diamoned to raise its temperature to 298 kelvin? But isn't it than just a kind of heat capacity? What happens if you did not transfer enough energy to make it exist stably at that temperature?

  1. The meaning of standard molar entropy values When seen in their relation to the energy content of a substance, standard molar entropy values, $S^0_{298}$, give useful insight that is absent when - as is usual - those J/K values are treated as merely abstract numbers to be added or subtracted in determining a $dS_0$ reaction . A $S^0_{298}$ value for a substance is the number of joules of energy/T transferred incrementally (reversibly, from the surroundings at each T) to a mole of substance from 0 K to 298 K. Thus, this number is a rough indicator or approximate index (not the joules dispersed at 298 K, nor the total joules dispersed from 0 K to 298 K!) of the relative amount of energy that the substance must have to be exist stably at 298 K. This is why $S^0_{298}$ values illuminate e.g., the difference in rigidity of bonding: the more rigid bonds of diamond (2.4 J/K) vs. the looser interatomic bonds in graphite (5.7 J/K) ,
Source Link
bananenheld
bananenheld
  • 109
  • 1

What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

What does it mean that the standard molar entropy value is the amount of energy that a substance must have to exist at a certain temperature?

According to this reference: http://khimiya.org/volume15/Entropia.pdf the meaning of standard molar entropy is the relative amount of energy that the substance must have to exist at for example 298 Kelvin.

An example is given of diamond and graphite, which has 2.4 J/K and 5.7 J/K respectively. I see that graphite has less strong bonds than diamond, i.e. diamond has higher potential energy stored inside its bonds. But I don't understand how that translates into a lower amount of energy needed to exist at a certain temperature? Is this the energy that needs to be supplied to the diamoned to raise its temperature to 298 kelvin? But isn't it than just a kind of heat capacity? What happens if you did not transfer enough energy to make it exist stably at that temperature?