Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Heronumber0 on 14/07/2007 21:08:09
-
If anyone can answer this to sufficiently satisfy me, I will be eternally grateful...Where to start? Oh yes - in biological systems, ATP is broken down to ADP and Pi (inorganic phosphate). The resultant free energy can drive chemical reactions.
I have read about phosphorylation (adding phosphate to make a covalent bond) of proteins, which can modify their function. So this makes sense. The inorganic phosphate can be used in this way.
However, Biologists talk loose and fast about free energy released from ATP hydrolysis and other reactions.
What form is this free energy in?
How does it drive other reactions?
In fact what is energy? - I have never heard a suitable answer to this question and I cannot answer it.
Please fell free to discuss...
-
Free energy is a concept that comes from thermodynamics. When a chemical reaction occurs it usually releases or absorbs energy this results in the chemicals involved in the reaction getting hotter or colder. Sometimes the conditions in which the chemical reaction takes place are such that the temperature is held constant. This can result in one chemical reaction that releases energy forcing another chemical reaction that absorbs energy.
This may sound a bit odd but it is not so peculiar when you think that many of the chemical reactions involved in organic chemistry are reversible in that given the right conditions the reactions can be made to go in either direction
-
Thanks soul surfer but are you saying that the free energy is actually heat energy?
-
I have often considered making connection to my domestic electricity supply before it is metered but the supply companies are very carefull to insulate all possible connection points and I can never see an inconspicuous way to do it.
-
If anyone can answer this to sufficiently satisfy me, I will be eternally grateful...Where to start? Oh yes - in biological systems, ATP is broken down to ADP and Pi (inorganic phosphate). The resultant free energy can drive chemical reactions.
I have read about phosphorylation (adding phosphate to make a covalent bond) of proteins, which can modify their function. So this makes sense. The inorganic phosphate can be used in this way.
However, Biologists talk loose and fast about free energy released from ATP hydrolysis and other reactions.
What form is this free energy in?
How does it drive other reactions?
In fact what is energy? - I have never heard a suitable answer to this question and I cannot answer it.
Please fell free to discuss...
Gibbs free energy G (there is also Helmoltz free energy H, less used), is defined as:
G = H -TS
where H is enthalpy, T temperature and S entropy. If you don't know what are H and S, ask.
G is useful when we compute its variations ΔG:
ΔG = ΔH - TΔS - SΔT (valid for small variations, otherwise you have to use differentials, instead). Quite important are transformation with constant T, so it becomes:
ΔG = ΔH - TΔS
ΔG is important because:
when ΔG is < 0 the reaction is thermodynamically spontaneous, that is, given the necessary activation energy, it happens.
when ΔG > 0, it can't happen. ΔG = 0 means thermodynamical equilibrium.
The formula for ΔG contains, essentially, ΔH and ΔS. It has this meaning: a reaction is spontaneous when it releases heat (ΔH < 0) or when it increases its entropy (ΔS > 0) or both.
Example 1): 2H2 + O2 --> 2H2O.
This reaction is exothermic = releases heat = ΔH < 0, but the entropy doesn't increase, ΔS is < 0, actually; so this reaction is spontaneous for the first reason and non-spontaneous for the second. Who wins? Simple, compute ΔH - TΔS, and you'll find that ΔH is more negative than how much - TΔS is positive, so the result is negative, and the reaction really happens.
Example 2): C(solid, graphite) + O2 --> CO2
ΔH < 0, ΔS > 0 so ΔG < 0. The reaction always happens.
Example 3): NH4NO3(solid) + H2O --> NH4+(aq) + NO3-(aq)
ΔH > 0 (endothermic), but ΔS > 0 and this more than compensate for the first, even at room T, so the result is ΔG < 0. Infact, NH4NO3(solid) really dissolves in water at room Temperature (the reaction is spontaneous) even if the process is endothermic: the solution's temperature lowers (a lot!)
Example 4): H2O(liquid, 25°C) --> H2O(vapour, 25°C); P = 1 atm.
ΔH > 0 (endothermic), ΔS > 0 but this is not enough, at 25°C: ΔH - TΔS > 0 so the reaction is not spontaneous. Can you guess at which T the reaction becoms spontaneous? Yes, at 100°C, you have guessed! Infact, it is just at 100°C that the term TΔS becomes = ΔH and so ΔH - TΔS is = 0 (thermodynamical equilibrium); just a little more than 100°C and ΔG < 0: water boils.
Actually, things are a bit more complicated than this, however this is quite good to start.
-
I have often considered making connection to my domestic electricity supply before it is metered but the supply companies are very carefull to insulate all possible connection points and I can never see an inconspicuous way to do it.
I have heard about strong electromagnets being used around the old-fashioned meters but I would never advocate breaking the law for this sort of inexpensive energy instead of totally free [;D]
-
Gibbs free energy G (there is also Helmoltz free energy H, less used), is defined as:
G = H -TS
where H is enthalpy, T temperature and S entropy. If you don't know what are H and S, ask.
G is useful when we compute its variations ΔG:
ΔG = ΔH - TΔS - SΔT (valid for small variations, otherwise you have to use differentials, instead). Quite important are transformation with constant T, so it becomes:
ΔG = ΔH - TΔS
ΔG is important because:
when ΔG is < 0 the reaction is thermodynamically spontaneous, that is, given the necessary activation energy, it happens.
when ΔG > 0, it can't happen. ΔG = 0 means thermodynamical equilibrium.
The formula for ΔG contains, essentially, ΔH and ΔS. It has this meaning: a reaction is spontaneous when it releases heat (ΔH < 0) or when it increases its entropy (ΔS > 0) or both.
Thanks for the elucidation. However, how were the tables made for entropy or ΔS? For example, if I look at the reaction:
2Ag+(aq) + Cu(s)→ Cu2+(aq) + 2Ag(s), the ΔS, for Cu 2+ (aq)under standard conditions is -100JK-1. Now I would have thought that ionisation and the loss of two electrons would actually stabilise the system because of the new electronic configuration of the copper ion so why is the entropy negative? The entropy for the Ag+ (aq) ion is definitely positive so why not for copper?
Moreover, another puzzle, this classical system releases more energy apparently than to make ΔS
positive. where does the extra 'free energy' go? And is free energy always released as heat?
So you have created another puzzle for my simple mind.
-
Gibbs free energy G (there is also Helmoltz free energy H, less used), is defined as:
G = H -TS
where H is enthalpy, T temperature and S entropy. If you don't know what are H and S, ask.
G is useful when we compute its variations ΔG:
ΔG = ΔH - TΔS - SΔT (valid for small variations, otherwise you have to use differentials, instead). Quite important are transformation with constant T, so it becomes:
ΔG = ΔH - TΔS
ΔG is important because:
when ΔG is < 0 the reaction is thermodynamically spontaneous, that is, given the necessary activation energy, it happens.
when ΔG > 0, it can't happen. ΔG = 0 means thermodynamical equilibrium.
The formula for ΔG contains, essentially, ΔH and ΔS. It has this meaning: a reaction is spontaneous when it releases heat (ΔH < 0) or when it increases its entropy (ΔS > 0) or both.
Thanks for the elucidation. However, how were the tables made for entropy or ΔS? For example, if I look at the reaction:
2Ag+(aq) + Cu(s)→ Cu2+(aq) + 2Ag(s), the ΔS, for Cu 2+ (aq)under standard conditions is -100JK-1. Now I would have thought that ionisation and the loss of two electrons would actually stabilise the system because of the new electronic configuration of the copper ion so why is the entropy negative? The entropy for the Ag+ (aq) ion is definitely positive so why not for copper?
The Cu2+(aq) is not simply a Cu2+ ion floating inside water, is much more than this, it's surrounded with many water molecules, more than in the case of Ag+, because of the greater charge. This locate water molecules around specific points, and so this reduces the entropy. In this kind of reactions we have to consider all the possible interactions and their relative ΔH and ΔS. Sometimes strange things happens because ΔH of hydratation is negative and more than how ΔH of lattice-demolition is positive: the result is that when you dissolve the salt in water the solution heats up! When the ΔH of solution in water of a salt is < 0 and ΔS is < 0 too because of what I have said, the result is also that an increasing in temperature decreases the solubility of the salt, instead of increasing it as usual. An example of this is Ce2(SO4)3:
http://www.sciencegeek.net/Chemistry/taters/solubility.htm
another one is Li2CO3.Moreover, another puzzle, this classical system releases more energy apparently than to make ΔS positive. where does the extra 'free energy' go?
Explain better, I haven't understood what you mean.And is free energy always released as heat?
No: a battery, for example, generates electric energy!
-
Thanks again for the detailed information. This is pretty interesting. However, the point I raised, and you answered, is that if enough energy is released to make ΔS>0 and there is extra energy left over, where does it go? For example in the reaction I menioned, 57.5 kJmol -1must change the system + surroundings to make it go ahead. The remaining 88.8 kJmol -1 is free energy. Why are mammals warm blooded, is it because we release free energy as heat?
However I am puzzled in the case of photosynthesis. How do electrons generate such a surfeit of energy and in which form is the energy? This needs a detailed explanation with respect to electron quanta and I find it difficult to understand. Can you help?
-
Thanks again for the detailed information. This is pretty interesting. However, the point I raised, and you answered, is that if enough energy is released to make ΔS>0 and there is extra energy left over, where does it go? For example in the reaction I menioned, 57.5 kJmol -1must change the system + surroundings to make it go ahead. The remaining 88.8 kJmol -1 is free energy.
Sorry but I can't understand what you mean in your question. Why are mammals warm blooded, is it because we release free energy as heat?
Certainly the conversion of free energy into electric or mechanical or chemical energy is never perfect ( that is, at 100%), so most of it goes into heat. I know nothing about Biology, but the existence of non-warm blooded (cold-blooded?) organisms certainly doesn't mean that they don't generate body heat at all; they only generate less, if this were your question.However I am puzzled in the case of photosynthesis. How do electrons generate such a surfeit of energy and in which form is the energy? This needs a detailed explanation with respect to electron quanta and I find it difficult to understand. Can you help?
Electromagnetic radiation's energy is converted into chemical energy by excitation of molecule's electrons. When a solar cell supplies a battery, it happens quite the same process.
-
Sorry about the unclear nature of my question lightarrow. Let me simplify the issue. It probably involves Biology as well as Chemistry and Physics.
I just wondered if so much free energy was generated in warm blooded animals that it got released as heat. With other temperature regulating mechanisms taking care of constant temperature.
My question, which you found unclear was: if a reaction needs 100kJ of energy to become spontaneous but 200kJ are released due to intermolecular rearrangements, in which form is this energy free? Heat or chemical potential or electrical?
Does this make a bit more sense?
I can visualise ATP broken down to inorganic phosphate which phosphorylates proteins but cannot imagine energy available for use by other processes unless we talk about activation energy in the form of heat. This would make sense to me.
-
Sorry about the unclear nature of my question lightarrow. Let me simplify the issue. It probably involves Biology as well as Chemistry and Physics.
I just wondered if so much free energy was generated in warm blooded animals that it got released as heat. With other temperature regulating mechanisms taking care of constant temperature.
My question, which you found unclear was: if a reaction needs 100kJ of energy to become spontaneous but 200kJ are released due to intermolecular rearrangements
Probably they are terms used in Biology, I can't understand them. in which form is this energy free?
Here I suspect the term "energy free" you are using has not the meaning of "free energy" used in Physics and Chemistry.I can visualise ATP broken down to inorganic phosphate which phosphorylates proteins but cannot imagine energy available for use by other processes unless we talk about activation energy in the form of heat.
This also is Greek for me.
Don't assume I'm an expert on the subject, I only have studied some years at univ. If you can make very precise examples then I could help you, in base of the few things I've studied, but I can't if you don't.
-
Dear Heronumber0
Quote-1 Question-1
“What form is this free energy in?
How does it drive other reactions?
In fact what is energy? - I have never heard a suitable answer to this question and I cannot answer it.”
Quote-2 Question-2
“However I am puzzled in the case of photosynthesis. How do electrons generate such a surfeit of energy and in which form is the energy? This needs a detailed explanation with respect to electron quanta and I find it difficult to understand. Can you help?”
Quote-1&2 and Question-1&2
Broth really have the same answer.
It is the radiation or transfer of;
energy / heat / at given wavelength of light.
Either at a very close distance as in a chemical reaction bonding
atomic systems [or] in a very long distance as in the light from the
Sun on a plant as the action of photosynthesis.
We get energy from gravity in hydroeolectric power stations. This is really energy from the sun because the heat of the sun evaporates the water from the ocean and sent it inland to rain on a mountaintop where the rivers run down and are collected in a hydroelectric dam and used to turn a generator.
Even wind generators energy comes from the sun heating the air making thermal air currents/ wind.
And even batteries give off free energy as heat when used.
Ed
-
This also is Greek for me.
Don't assume I'm an expert on the subject, I only have studied some years at univ. If you can make very precise examples then I could help you, in base of the few things I've studied, but I can't if you don't.
lightarrow - you were very helpful mate. You forced me to get my old books out to clarify my thoughts and you helped to clear up some dodgy misconceptions. We are all learning and I suppose I just have more to learn than others. Energy just is a difficult concept for me. Thanks for your contributions.
-
lightarrow - you were very helpful mate. You forced me to get my old books out to clarify my thoughts and you helped to clear up some dodgy misconceptions. We are all learning and I suppose I just have more to learn than others. Energy just is a difficult concept for me. Thanks for your contributions.
You're welcome!
-
Both really have the same answer.
It is the radiation or transfer of;
energy / heat / at given wavelength of light.
Either at a very close distance as in a chemical reaction bonding
atomic systems [or] in a very long distance as in the light from the
Sun on a plant as the action of photosynthesis.
We get energy from gravity in hydroeolectric power stations. This is really energy from the sun because the heat of the sun evaporates the water from the ocean and sent it inland to rain on a mountaintop where the rivers run down and are collected in a hydroelectric dam and used to turn a generator.
Even wind generators energy comes from the sun heating the air making thermal air currents/ wind.
And even batteries give off free energy as heat when used.
Ed
Thanks Ed,
My opinion is that the hydrolysis of ATP in biological systems generates enough 'local' heat energy to allow reactions between two reactants to occur by providing activation energy. In an enzyme substrate reaction, the 'local' heat energy allows either breakdown of the substrate into products or the synthesis of biomolecules (e.g. glycogen).
As for photosynthesis, I think that there may be an alternative to electrons transforming electrical potential energy to chemical potential energy in the form of ATP generated from ADP and inorganic phosphate. There may be a quantum explanation where electrons oscillate in superpositions of light-absorbing dyes in the plant until the most efficient photosynthetic pigment is chosen by collapse of the superpositions into one conformation of the pigment.
You are right in that the sun's energy is responsible ultimately, for hydroelectric and wind energy. However, geothermal energy results from radioactive element breakdown I think...and isn't the moon sufficient to generate tides for tidal energy?
-
You are welcome;
To quote you.
"However, geothermal energy results from radioactive element breakdown I think...and isn't the moon sufficient to generate tides for tidal energy?"
It is the radiation or transfer of;
energy / heat / at given wavelength of light.
Either at a very close distance as in a chemical reaction bonding
atomic systems [or] in a very long distance,
and even radioactive element breakdown comes in this area!
As for as the tidal energy, I would have to say that it comes from the two
gravitational fields pulling on the seas, as the moon goes by it pulls a bulge in the
sea and when it passes the earth's gravity pulls it back. It is a real tug-of-war that
creats energy.
Ed