If we are interested in how heat transfer is converted into doing work, then the conservation of energy principle is important. The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system. The first law of thermodynamics states that the change in internal energy of a system equals the net heat transfer into the system minus the net work done by the system. In equation form, the first law of thermodynamics is
Here is the change in internal energy of the system. is the net heat transferred into the system—that is, is the sum of all heat transfer into and out of the system. is the net work done by the system—that is, is the sum of all work done on or by the system. We use the following sign conventions: if is positive, then there is a net heat transfer into the system; if is positive, then there is net work done by the system. So positive adds energy to the system and positive takes energy from the system. Thus . Note also that if more heat transfer into the system occurs than work done, the difference is stored as internal energy. Heat engines are a good example of this—heat transfer into them takes place so that they can do work. (See Figure 15.3.) We will now examine , , and further.
The first law of thermodynamics is actually the law of conservation of energy stated in a form most useful in thermodynamics. The first law gives the relationship between heat transfer, work done, and the change in internal energy of a system.
Heat Q and Work W
Heat transfer () and doing work () are the two everyday means of bringing energy into or taking energy out of a system. The processes are quite different. Heat transfer, a less organized process, is driven by temperature differences. Work, a quite organized process, involves a macroscopic force exerted through a distance. Nevertheless, heat and work can produce identical results.For example, both can cause a temperature increase. Heat transfer into a system, such as when the Sun warms the air in a bicycle tire, can increase its temperature, and so can work done on the system, as when the bicyclist pumps air into the tire. Once the temperature increase has occurred, it is impossible to tell whether it was caused by heat transfer or by doing work. This uncertainty is an important point. Heat transfer and work are both energy in transit—neither is stored as such in a system. However, both can change the internal energy of a system. Internal energy is a form of energy completely different from either heat or work.
Internal Energy U
We can think about the internal energy of a system in two different but consistent ways. The first is the atomic and molecular view, which examines the system on the atomic and molecular scale. The internal energy of a system is the sum of the kinetic and potential energies of its atoms and molecules. Recall that kinetic plus potential energy is called mechanical energy. Thus internal energy is the sum of atomic and molecular mechanical energy. Because it is impossible to keep track of all individual atoms and molecules, we must deal with averages and distributions. A second way to view the internal energy of a system is in terms of its macroscopic characteristics, which are very similar to atomic and molecular average values.
Macroscopically, we define the change in internal energy to be that given by the first law of thermodynamics:
Many detailed experiments have verified that , where is the change in total kinetic and potential energy of all atoms and molecules in a system. It has also been determined experimentally that the internal energy of a system depends only on the state of the system and not how it reached that state. More specifically, is found to be a function of a few macroscopic quantities (pressure, volume, and temperature, for example), independent of past history such as whether there has been heat transfer or work done. This independence means that if we know the state of a system, we can calculate changes in its internal energy from a few macroscopic variables.
In thermodynamics, we often use the macroscopic picture when making calculations of how a system behaves, while the atomic and molecular picture gives underlying explanations in terms of averages and distributions. We shall see this again in later sections of this chapter. For example, in the topic of entropy, calculations will be made using the atomic and molecular view.
To get a better idea of how to think about the internal energy of a system, let us examine a system going from State 1 to State 2. The system has internal energy in State 1, and it has internal energy in State 2, no matter how it got to either state. So the change in internal energy is independent of what caused the change. In other words, is independent of path. By path, we mean the method of getting from the starting point to the ending point. Why is this independence important? Note that . Both and depend on path, but does not. This path independence means that internal energy is easier to consider than either heat transfer or work done.
Calculating Change in Internal Energy: The Same Change in is Produced by Two Different Processes
(a) Suppose there is heat transfer of 40.00 J to a system, while the system does 10.00 J of work. Later, there is heat transfer of 25.00 J out of the system while 4.00 J of work is done on the system. What is the net change in internal energy of the system?
(b) What is the change in internal energy of a system when a total of 150.00 J of heat transfer occurs out of (from) the system and 159.00 J of work is done on the system? (See Figure 15.4).
In part (a), we must first find the net heat transfer and net work done from the given information. Then the first law of thermodynamics can be used to find the change in internal energy. In part (b), the net heat transfer and work done are given, so the equation can be used directly.
Solution for (a)
The net heat transfer is the heat transfer into the system minus the heat transfer out of the system, or
Similarly, the total work is the work done by the system minus the work done on the system, or
Thus the change in internal energy is given by the first law of thermodynamics:
We can also find the change in internal energy for each of the two steps. First, consider 40.00 J of heat transfer in and 10.00 J of work out, or
Now consider 25.00 J of heat transfer out and 4.00 J of work in, or
The total change is the sum of these two steps, or
Discussion on (a)
No matter whether you look at the overall process or break it into steps, the change in internal energy is the same.
Solution for (b)
Here the net heat transfer and total work are given directly to be and , so that
Discussion on (b)
A very different process in part (b) produces the same 9.00-J change in internal energy as in part (a). Note that the change in the system in both parts is related to and not to the individual s or s involved. The system ends up in the same state in both (a) and (b). Parts (a) and (b) present two different paths for the system to follow between the same starting and ending points, and the change in internal energy for each is the same—it is independent of path.
Human Metabolism and the First Law of Thermodynamics
Human metabolism is the conversion of food into heat transfer, work, and stored fat. Metabolism is an interesting example of the first law of thermodynamics in action. We now take another look at these topics via the first law of thermodynamics. Considering the body as the system of interest, we can use the first law to examine heat transfer, doing work, and internal energy in activities ranging from sleep to heavy exercise. What are some of the major characteristics of heat transfer, doing work, and energy in the body? For one, body temperature is normally kept constant by heat transfer to the surroundings. This means is negative. Another fact is that the body usually does work on the outside world. This means is positive. In such situations, then, the body loses internal energy, since is negative.
Now consider the effects of eating. Eating increases the internal energy of the body by adding chemical potential energy (this is an unromantic view of a good steak). The body metabolizes all the food we consume. Basically, metabolism is an oxidation process in which the chemical potential energy of food is released. This implies that food input is in the form of work. Food energy is reported in a special unit, known as the Calorie. This energy is measured by burning food in a calorimeter, which is how the units are determined.
In chemistry and biochemistry, one calorie (spelled with a lowercase c) is defined as the energy (or heat transfer) required to raise the temperature of one gram of pure water by one degree Celsius. Nutritionists and weight-watchers tend to use the dietary calorie, which is frequently called a Calorie (spelled with a capital C). One food Calorie is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. This means that one dietary Calorie is equal to one kilocalorie for the chemist, and one must be careful to avoid confusion between the two.
Again, consider the internal energy the body has lost. There are three places this internal energy can go—to heat transfer, to doing work, and to stored fat (a tiny fraction also goes to cell repair and growth). Heat transfer and doing work take internal energy out of the body, and food puts it back. If you eat just the right amount of food, then your average internal energy remains constant. Whatever you lose to heat transfer and doing work is replaced by food, so that, in the long run, . If you overeat repeatedly, then is always positive, and your body stores this extra internal energy as fat. The reverse is true if you eat too little. If is negative for a few days, then the body metabolizes its own fat to maintain body temperature and do work that takes energy from the body. This process is how dieting produces weight loss.
Life is not always this simple, as any dieter knows. The body stores fat or metabolizes it only if energy intake changes for a period of several days. Once you have been on a major diet, the next one is less successful because your body alters the way it responds to low energy intake. Your basal metabolic rate (BMR) is the rate at which food is converted into heat transfer and work done while the body is at complete rest. The body adjusts its basal metabolic rate to partially compensate for over-eating or under-eating. The body will decrease the metabolic rate rather than eliminate its own fat to replace lost food intake. You will chill more easily and feel less energetic as a result of the lower metabolic rate, and you will not lose weight as fast as before. Exercise helps to lose weight, because it produces both heat transfer from your body and work, and raises your metabolic rate even when you are at rest. Weight loss is also aided by the quite low efficiency of the body in converting internal energy to work, so that the loss of internal energy resulting from doing work is much greater than the work done.It should be noted, however, that living systems are not in thermalequilibrium.
The body provides us with an excellent indication that many thermodynamic processes are irreversible. An irreversible process can go in one direction but not the reverse, under a given set of conditions. For example, although body fat can be converted to do work and produce heat transfer, work done on the body and heat transfer into it cannot be converted to body fat. Otherwise, we could skip lunch by sunning ourselves or by walking down stairs. Another example of an irreversible thermodynamic process is photosynthesis. This process is the intake of one form of energy—light—by plants and its conversion to chemical potential energy. Both applications of the first law of thermodynamics are illustrated in Figure 15.5. One great advantage of conservation laws such as the first law of thermodynamics is that they accurately describe the beginning and ending points of complex processes, such as metabolism and photosynthesis, without regard to the complications in between. Table 15.1 presents a summary of terms relevant to the first law of thermodynamics.
|Internal energy—the sum of the kinetic and potential energies of a system’s atoms and molecules. Can be divided into many subcategories, such as thermal and chemical energy. Depends only on the state of a system (such as its , , and ), not on how the energy entered the system. Change in internal energy is path independent.
|Heat—energy transferred because of a temperature difference. Characterized by random molecular motion. Highly dependent on path. entering a system is positive.
|Work—energy transferred by a force moving through a distance. An organized, orderly process. Path dependent. done by a system (either against an external force or to increase the volume of the system) is positive.
Kama tuna nia ya jinsi joto uhamisho ni kubadilishwa katika kufanya kazi, basi kanuni ya uhifadhi wa nishati ni muhimu. Sheria ya kwanza ya thermodynamics inatumika kwa kanuni ya uhifadhi wa nishati kwa mifumo ambapo uhamisho wa joto na kufanya kazi ni njia za uhamisho wa nishati ndani na nje ya mfumo. Sheria ya kwanza ya thermodynamics inasema kwamba mabadiliko ya nishati ya ndani ya mfumo ni sawa na uhamisho wa joto wa jumla katika mfumo wa nishati, minus kazi ya jumla iliyofanywa na mfumo. Sheria ya kwanza ya thermodynamics ni mabadiliko ya nishati ya ndani ya mfumo. ni joto la jumla kuhamishwa katika mfumo <unk> ambayo ni, ni jumla ya joto wote uhamisho ndani na nje ya mfumo. ni kazi ya wavu kufanyika na mfumo <unk> kwamba ni, ni jumla ya kazi yote kufanyika juu ya au na mfumo. "Kama ni chanya, basi kuna ""mfumo wa joto"" katika mfumo; kama ni chanya, basi kuna ""kazi ya wavu"" kufanyika na mfumo." Kwa hiyo, chanya huongeza nishati kwa mfumo na chanya huchukua nishati kutoka kwa mfumo. Hivyo. Kumbuka pia kwamba kama zaidi joto uhamisho katika mfumo hutokea kuliko kazi kufanyika, tofauti ni kuhifadhiwa kama nishati ya ndani. Injini za joto ni mfano mzuri wa hii - uhamisho wa joto ndani yao hufanyika ili waweze kufanya kazi. (Tazama Picha 15.3) Sasa tutachunguza, na zaidi. Sheria ya kwanza ya thermodynamics ni sheria ya kuhifadhi nishati iliyotolewa katika fomu muhimu zaidi katika thermodynamics. Sheria ya kwanza inatoa uhusiano kati ya uhamisho wa joto, kazi iliyofanywa, na mabadiliko katika nishati ya ndani ya mfumo. Uhamisho wa joto na kufanya kazi ni njia mbili za kila siku za kuleta nishati ndani au kuchukua nishati kutoka kwa mfumo. Utaratibu huo ni tofauti sana. Uhamisho wa joto, mchakato usio na utaratibu, husababishwa na tofauti za halijoto. Kazi, ambayo ni mchakato uliopangwa vizuri, huhusisha nguvu kubwa sana inayotumiwa kwa umbali. Hata hivyo, joto na kazi inaweza kuzalisha matokeo sawa. Kwa mfano, wote wanaweza kusababisha ongezeko la joto. Kuingiza joto katika mfumo, kama vile wakati jua linafanya hewa katika tairi ya baiskeli iwe joto, inaweza kuongeza joto lake, na hivyo inaweza kufanya kazi kwenye mfumo, kama vile wakati baiskeli inapopomba hewa ndani ya tairi. Baada ya ongezeko la joto kutokea, haiwezekani kujua kama lilitokana na uhamisho wa joto au kazi. Ukosefu huo wa uhakika ni jambo muhimu. Uhamisho wa joto na kazi ni wote nishati katika usafiri <unk> wala ni kuhifadhiwa kama vile katika mfumo. Hata hivyo, zote mbili zinaweza kubadilisha nishati ya ndani ya mfumo. Nishati ya ndani ni aina ya nishati tofauti kabisa na joto au kazi. Nishati ya ndani U Tunaweza kufikiria nishati ya ndani ya mfumo kwa njia mbili tofauti lakini thabiti. Ya kwanza ni mtazamo wa atomu na molekuli, ambao huchunguza mfumo katika kiwango cha atomu na molekuli. Nishati ya ndani ya mfumo ni jumla ya nishati ya kinetic na uwezekano wa atomu na molekuli zake. Kumbuka kwamba nishati ya kinetic pamoja na nishati ya uwezekano inaitwa nishati ya mitambo. Hivyo nishati ya ndani ni jumla ya nishati ya mitambo ya atomu na molekuli. Kwa sababu haiwezekani kufuatilia atomu na molekuli zote za mtu mmoja-mmoja, ni lazima tutende na wastani na usambazaji. Njia ya pili ya kuona nishati ya ndani ya mfumo ni katika suala la sifa zake macroscopic, ambayo ni sawa sana na thamani ya wastani wa atomiki na molekuli. "Kutokana na sheria ya kwanza ya thermodynamics, ""mfano wa nguvu ya ndani"" ni ""mfano wa nguvu ya ndani"" ambayo inategemea nguvu ya kinetic na nguvu ya uwezekano wa atomu na molekuli katika mfumo." Pia imegunduliwa kwa majaribio kwamba nishati ya ndani ya mfumo inategemea tu hali ya mfumo na si jinsi ilivyofika hali hiyo. Kwa mfano, joto ni kazi ya kiasi kidogo cha makroskopi (kiwango cha joto, shinikizo, na kiasi), bila kutegemea historia ya zamani kama vile kama kulikuwa na uhamisho wa joto au kazi iliyofanywa. Uhuru huu unamaanisha kwamba ikiwa tunajua hali ya mfumo, tunaweza kuhesabu mabadiliko katika nishati yake ya ndani kutoka kwa vigezo vichache vya macroscopic. Katika thermodynamics, sisi mara nyingi kutumia picha ya macroscopic wakati wa kufanya mahesabu ya jinsi mfumo tabia, wakati picha ya atomiki na molekuli inatoa maelezo ya msingi katika suala la wastani na usambazaji. Tutaona jambo hilo tena katika sehemu za baadaye za sura hii. Kwa mfano, katika mada ya entropy, mahesabu yatafanywa kwa kutumia mtazamo wa atomu na molekuli. Ili kupata wazo bora la jinsi ya kufikiri juu ya nishati ya ndani ya mfumo, hebu kuchunguza mfumo kwenda kutoka hali ya 1 hadi hali ya 2. Mfumo una nishati ya ndani katika hali ya kwanza na katika hali ya pili, bila kujali jinsi ulivyofikia hali yoyote. Kwa hiyo mabadiliko katika nishati ya ndani ni huru ya nini kusababisha mabadiliko. Kwa maneno mengine, ni huru ya njia. Kwa njia, tunamaanisha njia ya kupata kutoka hatua ya mwanzo hadi hatua ya mwisho. Kwa nini uhuru huo ni wa maana? Kumbuka kwamba. Wote na kutegemea njia, lakini haina. Uhuru huu wa njia inamaanisha kwamba nishati ya ndani ni rahisi kuzingatia kuliko uhamisho wa joto au kazi iliyofanywa. Mabadiliko ya ndani ya nishati: Mabadiliko sawa katika joto hutokezwa na michakato miwili tofauti: (a) Kwa mfano, mfumo una joto la 40.00J wakati mfumo unafanya kazi ya 10.00J. Wakati huo huo, joto la joto la J25.00 hutolewa nje ya mfumo na J44.00 ya kazi hufanywa kwenye mfumo. Ni nini mabadiliko ya jumla katika nishati ya ndani ya mfumo? (b) Nini mabadiliko katika nishati ya ndani ya mfumo wakati jumla ya 150 J ya joto uhamisho hutokea nje ya (kutoka) mfumo na 159 J ya kazi ni kufanyika juu ya mfumo? (Tazama Picha 15.4) Katika sehemu (a), ni lazima kwanza kupata uhamisho wa joto wa jumla na kazi ya jumla kufanyika kutoka kwa habari iliyotolewa. Kisha sheria ya kwanza ya thermodynamics inaweza kutumika kupata mabadiliko katika nishati ya ndani. Katika sehemu (b), uhamisho wa joto la jumla na kazi iliyofanywa hutolewa, kwa hivyo equation inaweza kutumika moja kwa moja. "Kama vile, ""Uhamisho wa joto wa jumla"" ni ""Uhamisho wa joto ndani ya mfumo minus uhamisho wa joto nje ya mfumo"" au ""Kazi ya jumla ni kazi iliyofanywa na mfumo minus kazi iliyofanywa kwenye mfumo"" au ""Mabadiliko ya nishati ya ndani ni kupewa na sheria ya kwanza ya thermodynamics.""" "Kwanza, fikiria ""J 40.00 ya uhamisho wa joto ndani na J 10.00 ya kazi nje"" au ""J 25.00 ya uhamisho wa joto nje na J 4.00 ya kazi ndani"" au ""Mabadiliko ya jumla ni jumla ya hatua hizi mbili"" au ""Mjadala juu ya a.""" "Hapa, ""mabadiliko ya joto"" na ""kazi ya jumla"" ni moja kwa moja na ""kufanya kazi"" na ""kufanya kazi"" ni moja kwa moja na ""kufanya kazi"" ni moja kwa moja na ""kufanya kazi"" ni moja kwa moja na ""kufanya kazi"" ni moja kwa moja." Kumbuka kwamba mabadiliko katika mfumo katika sehemu zote mbili ni kuhusiana na na si kwa mtu binafsi s au s kushiriki. Mfumo mwisho katika hali hiyo hiyo katika wote (a) na (b). Sehemu (a) na (b) zinaonyesha njia mbili tofauti kwa mfumo kufuata kati ya hatua sawa za kuanza na kumaliza, na mabadiliko ya nishati ya ndani kwa kila mmoja ni sawa - ni huru ya njia. Mabadiliko ya mwili wa binadamu na Sheria ya Kwanza ya Thermodynamics Mabadiliko ya mwili wa binadamu ni kubadilisha chakula katika uhamisho wa joto, kazi, na mafuta kuhifadhiwa. Uchanganuzi wa chembe za mwili ni mfano wenye kupendeza wa sheria ya kwanza ya termodynamics ikifanya kazi. Sasa tuangalie tena mada hizi kupitia sheria ya kwanza ya thermodynamics. Kwa kuzingatia mwili kama mfumo wa maslahi, tunaweza kutumia sheria ya kwanza kuchunguza uhamisho wa joto, kufanya kazi, na nishati ya ndani katika shughuli kuanzia usingizi hadi mazoezi mazito. Ni nini baadhi ya sifa kuu za uhamisho wa joto, kufanya kazi, na nishati katika mwili? Kwanza, kwa kawaida joto la mwili huhifadhiwa likiwa sawa kwa kuhamishwa kwa joto kuelekea mazingira. Hii ina maana ni hasi. Jambo jingine ni kwamba kwa kawaida mwili hufanya kazi juu ya ulimwengu wa nje. Hii ina maana ni chanya. Katika hali kama hizo, basi, mwili hupoteza nishati ya ndani, kwa kuwa ni hasi. Sasa fikiria matokeo ya kula. Kula huongeza nishati ya ndani ya mwili kwa kuongeza nishati ya kemikali (hiyo ni mtazamo unromantic ya steak nzuri). Mwili wetu huchanganua chakula chote tunachokula. Kimsingi, kimetaboliki ni mchakato wa oksidi ambapo nishati ya kemikali ya chakula hutolewa. Hii ina maana kwamba chakula input ni katika fomu ya kazi. Nishati ya chakula inaripotiwa katika kitengo maalum, kinachoitwa Kalori. Nishati hii hupimwa kwa kuchoma chakula katika calorimeter, ambayo ni jinsi vitengo vinavyoamuliwa. Katika kemia na biokemia, kalori moja (iliyoandikwa kwa herufi ndogo c) hufafanuliwa kama nishati (au uhamisho wa joto) inayohitajika kuongeza joto la gramu moja ya maji safi kwa digrii moja Celsius. Wataalamu wa lishe na wa kudhibiti uzito wa mwili hutumia kalori ya chakula, ambayo mara nyingi huitwa Kalori (inaandikwa kwa herufi kubwa C). Kalori moja ya chakula ni nishati inayohitajika kuongeza joto la kilo moja ya maji kwa digrii moja ya Selsiasi. Hii inamaanisha kuwa kalori moja ya lishe ni sawa na kilocalorie moja kwa kemia, na mtu lazima awe mwangalifu ili kuepuka kuchanganyikiwa kati ya mbili. Kwa mara nyingine tena, fikiria nguvu ya ndani ambayo mwili umepoteza. Kuna maeneo matatu ambayo nishati hii ya ndani inaweza kwenda - kwa uhamisho wa joto, kufanya kazi, na kwa mafuta yaliyohifadhiwa (sehemu ndogo pia huenda kwa ukarabati wa seli na ukuaji). Kuchukua joto na kufanya kazi huondoa nishati ya ndani kutoka kwa mwili, na chakula huirudisha. Ikiwa unakula kiasi sahihi cha chakula, basi wastani wa nishati yako ya ndani inabaki kuwa sawa. Kwa hivyo, kila kitu kinachopotea kwa joto na kazi, kinachobadilishwa na chakula, na kwa hivyo, kwa muda mrefu, inakuwa na faida. Kama wewe ni kula kupita kiasi mara kwa mara, basi ni daima chanya, na mwili wako kuhifadhi hii ziada ya ndani nishati kama mafuta. Kinyume chake ni kweli ikiwa unakula kidogo sana. Ikiwa ni hasi kwa siku chache, mwili huchanganya mafuta yake mwenyewe ili kudumisha joto la mwili na kufanya kazi ambayo inachukua nishati kutoka kwa mwili. Hii ni jinsi mlo wa chakula unavyosababisha kupoteza uzito. Maisha si rahisi kama ilivyo, kama vile mtu yeyote anayefanya mlo wa ziada anavyojua. Mwili huhifadhi mafuta au kuyabadilisha tu ikiwa ulaji wa nishati hubadilika kwa kipindi cha siku kadhaa. Baada ya kuanza mlo wa kawaida, mlo uliofuata haufaulu sana kwa sababu mwili wako hubadilisha jinsi unavyoitikia ulaji mdogo wa nishati. Kiwango cha msingi cha kimetaboliki (BMR) ni kiwango ambacho chakula hubadilishwa kuwa joto na kazi inafanywa wakati mwili uko katika mapumziko kamili. Mwili hupunguza kiwango cha kimetaboliki ili kulipia kiasi fulani cha kula kupita kiasi au kula kidogo. Mwili hupunguza kiwango cha kimetaboliki badala ya kuondoa mafuta yake mwenyewe ili kuchukua nafasi ya ulaji wa chakula uliopotea. Utakasikia joto la mwili kwa urahisi zaidi na kujisikia na nishati kidogo kwa sababu ya kiwango cha chini cha kimetaboliki, na hautapunguza uzito haraka kama hapo awali. Mazoezi ya mwili husaidia kupunguza uzito, kwa sababu hutoa joto kutoka kwa mwili wako na kazi, na huongeza kiwango cha kimetaboliki hata wakati wa kupumzika. Kupoteza uzito pia husaidia na ufanisi mdogo wa mwili katika kubadilisha nishati ya ndani kufanya kazi, hivyo kwamba hasara ya nishati ya ndani kutokana na kufanya kazi ni kubwa zaidi kuliko kazi iliyofanywa. Mwili hutupa ishara nzuri sana kwamba michakato mingi ya termodynamic haiwezi kubadilishwa. Utaratibu usioweza kubadilika unaweza kwenda katika mwelekeo mmoja lakini si kinyume chake, chini ya seti fulani ya hali. Kwa mfano, ingawa mafuta ya mwili yanaweza kubadilishwa kufanya kazi na kuzalisha uhamisho wa joto, kazi iliyofanywa kwenye mwili na uhamisho wa joto ndani yake haiwezi kubadilishwa kuwa mafuta ya mwili. La sivyo, tungeweza kukosa chakula cha mchana kwa kuota jua au kwa kutembea chini ya ngazi. Mfano mwingine wa mchakato wa termodynamic usioweza kubadilika ni photosynthesis. Utaratibu huu ni uingizaji wa aina moja ya nishati - mwanga - na mimea na kubadilisha kwake kuwa nishati ya uwezekano wa kemikali. Matumizi ya sheria ya kwanza ya thermodynamics ni kuonyeshwa katika Picha 15.5. "Mfano wa sheria ya kwanza ya thermodynamics ni kwamba sheria hizo zinaelezea kwa usahihi mwanzo na mwisho wa mchakato tata kama vile ""metabolism"" na ""photosynthesis"" bila kujali matatizo ya kati." Tabla ya 15.1 inaonyesha muhtasari wa maneno yanayohusiana na sheria ya kwanza ya thermodynamics. <unk>Nishati ya ndani<unk>jumla ya nishati kinetic na uwezekano wa mfumo wa atomu na molekuli. Inaweza kugawanywa katika makundi mengi madogo, kama vile nishati ya joto na kemikali. Inategemea tu juu ya hali ya mfumo (kama vile yake,, na,) si juu ya jinsi nishati aliingia mfumo. Mabadiliko katika nishati ya ndani ni njia huru. _Heatnishati kuhamishwa kwa sababu ya tofauti ya joto. Inajulikana kwa mwendo wa molekuli wa nasibu. Inategemea sana njia. Kuingia katika mfumo ni chanya. <unk> Kazi nishati kuhamishwa na nguvu kusonga kwa njia ya umbali. Utaratibu uliopangwa vizuri na wenye utaratibu. Njia inategemea. Mfano wa mfumo wa umeme (kwa nguvu ya nje au kwa kuongeza kiasi cha mfumo) ni chanya.