Q&A for lesson 1

8/7/2019 Q&A for lesson 1

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Q&A for lecture on the first lesson

Dear Folks

To be an effective learner, you will have to be more critical in the understanding

and usage of scientific terms. Please remember that very often the scientific

meaning of a word can be different from its meaning in English.

Also, pleaseplease, read through the Q&A and give yourself ample time tothink deeply about the subject matter. Do not wait until the exam time to do so.

The number of Q&As involved can be overwhelming.

Do not hastily formulate questions and raise them. It is important for you to learn

to raise high order questions, but it is even more important for you to learn to

construct answers to your (and others) questions. You should then, throughdiscussion, compare and contrast your answers with those of your peers (or with

mine in the Q&A) to check on the correctness of your understanding on the subjectmatter.

Below, please see the questions raised by your classmates and my answers to them.

To facilitate you learning, I have also uploaded a 16 min video clip to ivle as extra

lesson or tutorial on Thermodynamics. Please view them at your leisure.

Best wishes

Prof Ip

Feb 26 2010

1. What are the 7 vital signs of life you mentioned in the lecture? According to

what I have learned, they are:

1) complex and organized (in hierarchical manner);

2) requiring energy;

3) respond to environment (both internal and external);4) reproduce;

5) grow;

6) genes as the units of heredity;

7) adapt to changes OR living things, collectively, have the capability to evolve.


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The 7 vital characteristics of living organism are: (1) nutrient intake, (2)

respiration, (3) excretion, (4) locomotion/movement, (5) irritability/sensibility, (6)

growth, and (7) reproduction.

2. In slide 18 of Lecture 1 (Whats the meaning of G?), in the definition of -

G, if the process is reversible is mentioned. Why is it necessary for theprocess to be reversible?

A thermodynamically reversible process is one that can go from the initial state to

the final state and then from the final state back to the initial state without

producing any change in the universe, that is, it defy the second law of

thermodynamics and no energy has been converted to a less useful type (more

disordered type) of energy, e.g. heat. Hence, the statement means thatdelta Grepresent theoretically the maximum amount of energy that can be used to do

biological work if no heat is produced. However, this would occur only in theorybecause the portion of delta G that turns into heat cannot be used to do biological

useful work in real life situation.

3. Base on the 2nd

Law of Thermodynamics, can I say that the entropy of our

physical universe (an isolated system) always increases as there are always some

spontaneous thermodynamic processes taking place in the universe?

Yes, that is correct.

4. Do the concepts of enthalpy and Gibbs free energy apply to our physical

universe?

Yes, it applies to process taking place on Earth an Earth is part of our physical

universe.

5. Am I right to say that entropy, enthalpy and Gibbs free energy do not apply to

any isolated system inside another isolated system as no energy transfer takes

place?


6. Entropy is a representation of energy stored within orderness, that is, a system inan ordered state would have higher entropy than the same system in a disordered

state. May I politely say that this statement is incorrect? As the higher the entropy,

the more disordered a system is.

The statement should be read as Entropy is a representation of energy storedwithin orderness, that is, a system in an ordered state would have more energy


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stored as entropy (but mindful that entropy is an expression of disorderness) than

the same system in a disordered state.A system with higher entropy is moredisordered and contains less energy stored in the form of orderness.

7a. I was confused when I read this statement, "For a thermodynamic process that

goes from an initial state of low disorderness (S1) to a final state of high

disorderness (S2), energy is given out."

This statement is correct.

7b. My perception was that if a process goes from an initial state of low

disorderness to a final state of high disorderness, this means that there is an

increase in entropy.

No. Entropy represents disorderness, but energy is stored within orderness. Since a

system would like to go from a high energy state to low energy state, with respect

to entropy alone, the system would go from high orderness, that is low

disorderness with a low entropy by value, to low orderness, that is high

disorderness with a high entropy value.

7c. This means that the molecules in the system are more chaotic eg. the moleculeshave more energy. Doesn't this mean that energy is taken in by the system?

No. I am afraid you misunderstood the whole concept of entropy. Entropy as a type

of energy is distinctly different in concept (although related to a certain extent)from the kinetic energy of molecules which is a manifestation of temperature.

Please visit the website that I have suggested on thermodynamics and see whetherthe information there can facilitate your understanding on this.

7d. Am I right to say that ice has low disorderness and liquid water has high

disorderness? And for ice to melt to become liquid water, energy should be taken

in?

It depends on whether you are talking about delta G, delta H or delta S. For ice

melting at room temperature, delta H is positive meaning that heat is absorbed withan increase in enthalpy, delta S is also positive meaning that there is an increase in

entropy and energy stored in orderness is given out, and the overall Gibb's free

energy is negative meaning that energy is release in the process from the system to

the surrounding.


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There are detailed explanations in the Q&A on this, including an example of how

delta G is calculated for ice melting at room temperature. Please go through the

Q&A to facilitate your learning.

8. I do not understand the meaning of reversible in this statement: - delta G=

maximum amount of energy theoretically available for the system to do biological

useful work on its surrounding when the system goes from initial state to final state

if the process is reversible. Please help.

Here, I refer to thermodynamic reversibility (which is different from kinetic

reversibility). A thermodynamically reversible process is one that can go from the

initial state to the final state and then from the final state back to the initial state

without producing any change in the universe, that is, it defy the second law of


disordered type) of energy, e.g. heat. Hence, the statement means thatdelta Grepresent the amount energy theoretically the amount of energy that can be used to

do biological work if no heat is produced. However, this would occur only in

theory because the portion of delta G that term into heat cannot be used to do

biological useful work.

9a. Isolated system cannot exchange heat, energy and matter.

Closed system can exchange heat and enery but not matter.

Open system can exchange anything with its surrounding.

Now, I want to raise some questions: Since heat is a kind of energy, why we have

to separate it to the other types of energy when defining these terms?

This is because scientist has defined one more type of system: the adiabatic

system, which deals with heat specifically. An adiabatic system is one in which

processes occur without gaining or loosing heat from the surrounding.

9b. And what does energy means in these particular concept? Does energyimply all the other types of energy?

Yes, energy here implies all other types of energy except heat.

9c. About isolated system, when we consider a system as isolated one, it implies

that such system is isolated from the surrounding and other system. The universe

alone is also defined to be isolated but from what surrounding or systems is it

isolated? Is it likely that we just assume the physical universe is isolated system

because there is only one universe that we have known?


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Yes. Also, we do not know what is outside the physical universe at present.

9d. In your note, it is written that the second law of thermodynamics states that

The total entropy of any isolated thermodynamic system always increases overtime, i.e. the occurrence of thermodynamic processes would increase the entropy

of the universe. This is because the physical universe is an isolated system. Thesecond law of thermodynamic deals with the universe, i.e. the system and its

surrounding, and it does not deal with the system alone. I was a bit confused when

I read this part. I dont see any cause and effect relationship between the fact that

the universe is an isolated system and the increasing in its entropy over time. Can

you explain more about this?

It is essential to understand the physical universe as an isolated system; only then

the first law of thermodynamic would hold, i.e. the amount of energy present in theuniverse is constant. Based on this, we can understand that thermodynamic

processes occurring in any system in the universe would involve the transformation

of energy from one type to another with more and more energy being turned into

the more disordered type, i.e. heat.

10. -G = the maximum amount of energy theoretically available for the system todo biological useful work on its surrounding when the system goes from initial

state to the final state if the process is reversible. Why the mention of if the

process is reversible in the above definition? Even if the process is not reversible,

the system would still be able to proceed from initial state to the final state,

wouldnt it?

A thermodynamically reversible process is one that can go from the initial state to

the final state and then from the final state back to the initial state without

producing any change in the universe, that is, it defy the second law of


disordered type) of energy, e.g. heat. Hence, the statement means thatdelta G

represent theoretically the maximum amount of energy that can be used to do

biological work if no heat is produced. However, this would occur only in theorybecause the portion of delta G that term into heat cannot be used to do biological

useful work.

11. I am not very clear with the concept of Gibbs free energy on the example of ice

melting. In Q& A page 1, last paragraph, the process of ice melting at room


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temperature at 25 C. The process occurs spontaneously because delta G is negative

in value. However, the process is endothermic so there is a positive change in delta

H meaning that the system gains in heat content and For an endergonicprocess to occur, delta G is positive, meaning that energy supply to the system is

required Similarly, on the notes, it also indicates that positive delta G equals toendergonic reaction and negative delta G is exothermic reaction. Is the example of

ice melting an exception of endergonic reaction? Does negative delta G value

always indicate an exergonic reaction?

It is important for students of science to critically understand the meaning of terms

and use them critically. Please take note of the following:

a. Negative delta G = exergonic, spontaneously occurs in that directionb. Positive delta G = endergonic, non-spontaneous in that direction (but

spontaneous in the opposite direction)

c.

Negative delta H = exothermicd. Positive delta H = endothermicIt is therefore incorrect to state that negative delta G is exothermic. Delta H does

not govern the spontaneity of the reaction, but delta G does. For a reaction that has

a positive delta G, it would not occur spontaneously in that direction, but if the

system is supplied with an amount of free energy larger than the required delta G

value (for any thermodynamically irreversible process), the reaction would take

place. For ice melting at 25oC, delta G is negative, despite delta H being positive,

because of a large + delta S value. Substitute those into the equation G =H + (-TS) and you can understand a better.

12a. In the sentence "the system to do biological useful work on its surrounding",

what does "biological useful work" mean?

There are three types of biological useful work: (1) formation and/or maintenance

of electrochemical gradients, (2) synthesis of biomolecules and (3) mechanical

movements.

12b. In my opinion, biological useful work should always be done by the

environment to a biological system.

I don think that is correct.

12c. On page 26, can we understand the delta G=-420000 cal/mole as following:

(1) This is the change in Gibbs Free Energy if we couple the two reactions

together. And this overall reaction is exergonic.


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(2) This is also the amount of energy that transfers to heat during ATP synthesis.

Firstly the phrase during ATP synthesis should be change to during the couplingbetween glucose oxidation and ATP synthesis through substrate and oxidative

phosphorylation. Secondly, yes the portion of energy that is not used to do workwould be finally released as heat.

12d. According to 2nd law of thermodynamics, can we say that our universe will

eventually end up in pure energy of heat without other types of energy?

Yes, conceptually that is correct.

12e. For the synthesis of biomolecules as biologically useful work,do we do this

work to the enviroment or ourselves? I think we do this for ourselves but not the

environment right?

In science, it is of utmost importance to know the exact scientific meaning of the

words, which can be different from the common English meaning, so that

communication would be clear and exact.

In thermodynamics, system and surrounding has their own scientific meaningalthough they are English words. Surrounding as a thermodynamic term is not

the same as environment.System can be defined as a chemical reaction takingplace in a small compartment with a cell, a protein or a group of protein, an

organelle, a cell, a tissue, a organ, an organism, a population, and etc, and anythingoutside that system is defined thermodynamically as the surrounding. The

system and the surrounding equal to the universe.

You have apparently taken my explanation in thermodynamics e.g. surrounding, as

the environment. Perhaps, you can understand it better if you can critically

evaluate the meaning of these terms to you (how did you learn thermodynamic

previously?) so that you can use them correctly. It is important to unlearn and

relearn.

12f. I got it. When we do biologically useful work, the surroundings can include

ourselves. Is this correct?

Think it this wayFor the reaction of ATP hydrolysis, it can go from a initial state

of high energy content of ATP to a low energy content of ADP + Pi, and this

constitutes a system. The energy released can be used to do work on the


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surrounding (which include the other parts of the cell) to transport molecules, to

produce mechanical movement or to synthesis biomolecules. Hence, in coherent

with the way physics understand work done, the system (ATP hydrolysis) is doing

work on its surrounding, because the surrounding include anything outside the

system including the ribosome, plasma membranes..and etc. This is only anexample, and you will have to think more about it in order to fully understand it.

12g. I think I have come up with another example: In the light reaction of

photosynthesis, if we consider the electron transport chain as a system, then the

rest will be its surrounding. The energy of the electric gradient is finally used by

NADP reductase, which converts NADP into NADPH. In this way a system does

biologically useful work to its surrounding. Is it a correct example?

Yes, your understanding is correct. And, the fact that you can apply the concept to

come up with another example means you have achieve deep learningalearning approach that you should apply to all learning processes. I am happy for

you

13. Pertaining to your earlier lecture on 2nd law of thermodynamics, I understand

that energy should flow from a higher energy state (higher ordered structure) to a

lower energy state (lower ordered structure). In the case of the egg to a highly

ordered organism such as the cow, how will this be made possible? Is this due to

energy transformation or does this defy the 2nd law of thermodynamics?

The second law of thermodynamics addresses the universe (system plus

surrounding), and should not be applied to a system (e.g. egg to cow). With all the

biological activities, the system plus the surrounding (e.g. the earth and hence the

universe) would increase in disorderness.

14a. "In general a reversible process requires an absence of friction, a balancing

of internal and external forces (i.e. only infinitesimal changes can be made in a

given step), and time to reestablish equilibrium after each infinitesimal step. When

these conditions are not met, the process is irreversible." Based on my

understanding, i would say that thermodynamic reversibility allows system to stayin energy equilibrium with its surrounding.

No, that is not correct. For a system to be in equilibrium with its surrounding, there

can only be one state as defined by the functions of state. However, for a

thermodynamically reversible process, there are clearly defined initial state and


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final state; if not there wont be any process because of the existence of only onestate.

14b. This process can occur when there's opposing infinitesimal changes being

applied to the system under a few conditions to ensure there is no heat loss. Am igetting it right?

No, that is not correct. In a thermodynamically reversible process, no heat is

producednot no heat loss.

14c. Can you give me a few examples of the internal and external forces mentionedin the statement above?

I cannot give you an example, because this is only a theoretical example involving

a theoretical analysis using the calculus approach. In reality I know of nothermodynamically reversible process.

14d. While trying to understand the lying mechanism of the concept on how this

thermodynamic reversible process defy the 2nd law of thermodynamics, I came

across this in wikipedia: A reversible process changes the state of a system in such

a way that the net change in the combined entropy of the system and its

surroundings is zero. In layman's term, is it because when the system becomes

more disordered, it is compensated by surrounding getting more ordered and viceversa and hence the net change of zero entropy?

Once again, this is only a theoretical example. Here, the concept of entropy should

not be viewed as orderness, but understood as no increase in energy of highlydisordered type like heat in the universe.

14e. Is Carnot cycle only theoretically hypothesised?

No.

14f. If not, can you tell me a few applications that this cycle is involve in?

Calculating the efficient of heat engines.

15a. Am I right to say that neither energy transfer nor energy transformation can

achieve 100% efficiency in reality?



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15b. In slide 7 of Lecture 1 (Different forms of energy), are all different forms of

energy listed here arranged in such an order that the forms of energy higher in the

list is of higher quality (more available to do work; more ordered) and the forms of

energy lower in the list is of lower quality. For example, energy of rotation is of

higher quality/more ordered compared to energy of orbital motion.

Yes, that is correct in general. However, please take note that some of the items in

the list share the same rank of orderness.

15c.Could you give some examples for energy of rotation?

Examples include the rotation of earth along its axis and the rotation of twin(binary) stars. For instance, the Earth has a rotational kinetic energy of 2.1410

29J.

15d. I remember you mentioned in the lecture that transformation from a higherquality energy form to a lower quality energy form can achieve 100%efficiency, but not vice versa. This seems to contradict the fact described in a)

above. Is it because that, theoretically, 100% efficiency can be achieved when a

higher quality energy form istransformed into a lower quality energy form,

but not in reality?

It should be ..from a higher quality energy form to, heat, which is a lower

quality energy form can achieve 100% efficiency...

15e. "Transformation from a higher quality energy form to, heat, which is a

lower quality energy form, can achieve 100% efficiency, but not vice versa.".In the above statement, there is an assumptionheat is the least ordered form of

energy. Hence, to put the above statement in a more precise way, transformation

from any form of energy to the least ordered form of energy can achieve 100%

efficiency; and this is the only case in which 100% efficiency of energy

transformation can be achieved.

At present, scientists general accept that heat as the least ordered (or mostdisordered) form of energy on Earth. Your statement transformation from anyform of energy to the least ordered form of energy can achieve 100% efficiency;

and this is the only case in which 100% efficiency of energy transformation can be

achieved. is acceptable.


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16. It is wrong to say that chemical engines convert chemical energy to

mechanical energy. (In Q&A, No.5) But is it right to say chemical enginestransformchemical energy to mechanical energy?Yes, I agree with you that transform is a more appropriate word than convert.

16. In my opinion, no forms of energy can be directly converted to any other form

of energy. It can only be transformed; that is, one form of energy can only be

released and captured by a transducer, which eventually results in the increase in

another form of energy (coupling). Am I right?

Not quite. Energy can be transformed from one type to another through any

spontaneous process that occurs within a system. And, naturally, some of the

energy released would be transformed to heat even in the absence of an appropriate

transducer.

END

Q&A for lesson 1

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