Thermodynamics
1) Which it is the scope of the thermodynamics:
It studies macrocospic variable macrocospic systems using to the aim to determine if the system is in equilibrium and if it it is not, towards which equilibrium stretches.
2) From what the state of a system is defined:
From the value of the macrocospic property that can be extensive if mass, volume depend on q.ta the total of present matter () or intensive if of they are independent (density, pressure).
3) What is one state function:
It is a variable thermodynamics that assumes an only value and very determined when the system is found in determining be.
4) When a system is closed:
When they are not possible exchanges of matter with the atmosphere.
5) When a system is isolated:
When they are not possible exchanges of energy with the atmosphere.
6) When a process is reversible:
When it makes yes that the sure value of a variable one that characterizes the system in a data moment only differs of an infinitesimal amount from the same value of variable in the successive moment in such a way the process is to ollow itself of states of thermodynamic equilibrium.
7) When a process is irreversible:
When the value of a variable one that characterizes the system in a sure moment defers of one ended amount from the same value of the variable one in the successive moment.
8) When a transformation is spontaneous:
It is a transformation that has place without that the participation of external forces is necessary. All the spontaneous transformations are irreversible.
9) What is and like the heat is defined:
It is an energy shape that is transmitted between 2 points of a system that they are found to 2 various temperatures. The measure unit is the calorie, that is the amount of heat necessary in order to increase the temperature of a gram of water from 14,5 15,5°C.
10) What is the temperature:
It is an index of the attitude of a body to yield heat to an other body or to receive some.
11) What is the energy:
It is the ability to produce job, they exist some of various types, and one of these is the heat which perhaps he is less noble in difficultly ritrasformabile how much in the energy shape that has generated it
12) Describe the mechanical job, that one of expansion and the unit of measure for this last one?
The mechanical job is the product of the force for the movement, for gases is preferred to speak about the expansion job
L = Pressione * DVolume. Measure in liter-atmosphere.
13) 1 liter atmosphere = x Joule :
1 liter atmosphere = 101,33 Joule ?
14) 1 liter atmosphere = x cal :
1 liter atmosphere = 24.2 cal ?
15) 1 cal = x Joule :
1 Cal = 4,184 Joule ?
16) Describe the job electrical worker and the unit with which it comes expressed:
It is the product of loads electrical worker for the potential difference them. The measure unit is the Joule.
17) That convention is used for the sign of the job:
The job is positive if it is made from the system while it is negative if it is made from the atmosphere on the system.
18) That convention is used for the sign of the heat:
The heat is positive if it is absorbed from the system while it is negative if it is yielded from the system to the atmosphere.
19) Enounce 1° the principle of the thermodynamics:
The energy cannot be created some right yed but only transformed. In formulas DU = Q - L.
A formulation that of is one directed consequence is that the inner energy of an isolated system is constant.
20) What is the inner energy U:
It is variable extensive an own one that as an example depends on the inner characteristics of the system which the kinetic energies tied to the motion of electrons, it can be altered only changing the state of the system as an example passing from the solid state to that liquid in the which case the variation of inner energy is equal to the difference between the energy necessary in order to form the ties of the products and that necessary one in order to break off the ties of reagents.
Based on 1° the principle of the thermodynamics it is one state function and its variation
DU = Q heat - L job
solo from the state depends begins them and final.
21) That types of transformations are possible that L jobrespects D U = Q heat -:
Adiabatic, isocore, isobars.
22) When a process is said adiabatic:
When not there is exchange of heat between the system and the atmosphere, in such case DU = - L.
23) When a transformation is isocora:
When it happens to constant volume. To notice that for a chemical reaction the job is of expansion which is proporziona them to the volume variation, if the reaction happens to constant volume the job is null DU = Q.
24) When a transformation is isobar:
When it happens to constant pressure, the exchanged heat to constant pressure is Q = DU PDV.
25) What is the H entalpy of a system:
The entalpy is tightened relative of the inner energy and in practical of it it represents just a correction in order to explain the job that the gases complete in a chemical reaction in the comparisons of the external pressure. The entalpy differs from the energy of some point percentage.
It is defined from the relation H = U PV. in the case that the transformation is isobar, the pressure variation is null and therefore DH = Q that is the entalpy corresponds to the exchanged heat to constant pressure. It is one state function.
26) Fare a reaction example that happens to constant pressure:
Every reaction that happens to the open air where the pressure at sea level turns out equal to 1 atm.
27) That what ¨ the termochimica:
It is a science that studies the heat exchanges associates you to the reactions chemistries.
28) When a transformation is exothermic:
When the system develops heat that yields to the atmosphere, tasks to the combustion of methane.
29) When a transformation is endothermic:
When the system absorbs heat from the atmosphere, tasks to the passage from ice to water.
30) When a transformation is termoneutrale:
When it is not accompanied from measurable thermal effects.
31) For what stà the H symbol that characterizes the entalpy:
It stà for Heat, heat in how much for the reactions to constant pressure the heat variation identifies itself with the entalpy variation. Tasks to H and Or that they form the water, the water introduces an inner energy that is sure inferior to the energy of 2 gases where the kinetic energy is elevated, that it is translate in the fact that this process will have necessarily to yield energy to the atmosphere and it will make it under heat shape and therefore the entalpy variation will be negative in how much the intrinsic heat of the system will be yielded to the atmosphere, the reaction will be exothermic.
32) What is the entalpy standard DH°, which it is the measure unit and what indicates:
It is the variation of entalpy DH° reported to 1 size when it is the reagents that the products are in the reference conditions.
If the reaction is exothermic then DH° = Q yielded Q is negative being therefore negative.
If the reaction is endothermic then DH° = Q absorbed Q is positive being therefore positive.
Measure in Kcal/size and indicates the heat absorbed or yielded from the process.
33) Why in termochimica D H is usedprettamente instead rather than DU:
Why DU corresponds to the variation of heat for the reactions to constant volume while DH corresponds to the variation of heat for the reactions to constant pressure, and inasmuch as nearly all the reactions chemistries happen to atmospheric pressure which is constant, DH is the interested function of state.
34) What is the entalpy standard of combustion DHc°:
It is the entalpy variation standard associated to the reaction of combustion of a compound size considered in gaseous oxygen excess as a result of which the contained C and the H in the substance give origin to 2CO and H2Or.
Size of the compound represents therefore how much free heat to continuation of the combustion of one.
35) How much is worth the entalpy standard of combustion DHc° of the C2H4 :
Reaction combustion: C2H4 2 3Or ® 2 CO2 2 H2Or
therefore based on the law of Hess: DH°f (C2H4) = 2H°f (CO2) 2H°f (H2Or) - H°f (C2H4)
Memories that H°f (Or2) = 0 for definition, cosiccome for all the single elements and not to the state of compound.
36) If you know the DH° associated to the combustion of a mixture and i DassociatedH° C to the combustions of the single elements of the mixture, as the three values are legacies:
- DH° (miscela) = DH°c (comp_1) * (n°moli comp_1) DH°c (comp_1) * (n°moli comp_2)
it is multiplied for the wharves in how much DH is an extensive function of state, that it depends cioà on the matter amount.
37) What is the entalpy molar standard of H formationf°:
It is the entalpy variation standard that accompanies the formation of 1 size of the compound (in its state standard) to leave from the elements that compose it, also they in their state standard.
38) How much is worth the entalpy molar standard of H formationf° for all the single elements:
It is worth 0 for convention, that concurs relative measures of entalpie of a system.
39) What is the thermal tonality of a reaction and from what it is influenced:
It is the heat freed or supplied to constant pressure and is equivalent to the variation of H. entalpy It is tied to the amount of considered matter, the physical conditions and the state of aggregation of reagents and products. In order to conform it, as mass always refers to us to a size while as physical conditions 1 atmosphere is chosen 25°C and, like state of aggregation, finally, is chosen that one in which the substance he is stabler in these conditions.
40) Enounce the law of Hess:
The thermal tonality of a reaction depends solo from the state begins them and final of reagents and the products, while he is independent from the number of the intermediate processes and from the order with which they are it realizes to you. This law concurs of calculating those not calculable heats of reaction algebricamente experimentally.
41) Enounce the consequence of the law of Hess that with to the concept of combustion heat concurs the calculation of the entalpy standard of H formationf° of one substance:
The entalpy variation standard of a reaction, DH° is equal to the sum of the entalpie standard of formation, Hf°, of the products of reaction, except the sum of the entalpie standard of formation, Hf°, of reagents. All the values of Hf° must be multiply you for the stoichiometric coefficient with which the relative substance it appears in the reaction.
For the reaction aA bB ® C dD
DH° = c Hf°(C) d Hf°(D) - to Hf°(A) - b Hf°(B)
42) What is the dissosciation energy:
It is the entalpy variation standard of the reaction that door to the breach of the tie in issue, indicates therefore how much energy is necessary to employ in order to break off the tie that holds united atoms of the substance.
43) What is the medium energy of tie:
If a molecule contains n ties all equal ones, the medium energy of tie is the entalpy variation standard of the reaction associated to the breach of all the ties uniform for the number of these ties. It is characteristic of a data tie independently from the particular considered molecule and for this they exist of the tables with these values for the more common ties. Often these compounds are stabler than how much calculating theoretically.
44) What is the resonance energy:
It is the difference between the value experiences them of the entalpy standard of H formationf° and the deliberate value of the medium energies of tie. It happens in the structures like aromatic compounds us where there are double ties or triple he stabilizes to you for resonance.
45) the breach of a tie involves one variation Dpositive or negative H°:
It involves a positive variation in how much is necessary to supply heat to the substances affichè the electrons they are carried on the more external layers and can therefore be routes the ties that they hold with the molecule.
46) What is the S entropy of a system and which it is its unit of measure:
It is a function of state defined for a system closed in which transformation to constant temperature happens one, exchanging with the atmosphere the Q heat.
If the transformation is reversible 
the system
is in equilibrium in fact a
reversible transformation can be thought like one indefinite
succession of states of equilibrium.
If the transformation is irreversible 
the system spontaneous transformation is center of one.
If moreover the system is also block, then Q = 0, therefore:
DS = 0 arranges in equilibrium
DS > 0 the system is center of one spontaneous transformation.
Measure in calories/K otherwise called entropica unit.
47) Why one says that the entropy is the arrow of the time:
Why we can distinguish between two instantaneous released in moments various one and regarding the same phenomenon and to deduce which it has been released before simply on the base that in it you must be minor disorder.
48) Enounce 3° the principle of the thermodynamics:
The solid entropy of crystalline puro a S° is null to the temperature of the zero assoluto. This principle concurs to calculate the entropy of a system to one any temperature and to observe that it depends on the complexity of the molecule and in the reactions chemistries increases if it increases the n° of wharves of substances to the gaseous state.
This stà to identify that to 0 K exists a single way in order to hold united atoms in a crystalline reticulum, therefore the state of order is maximum, with increasing of the temperature increases the disorder.
49) To which characteristics of the substance in issue the entropy is tied molar:
the entropy grows with the complexity of the molecule therefore for the diamond that is more symmetrical regarding the grafite, the entropy is inferior.
Moreover the entropy grows in the passages solid liquid® ® gas.
50) Which are the criteria that characterize the spontaneità of one definitively transformation:
a) Every system stretches to catch up the minimal content of energy.
b) the entropy of the system and therefore the disorder degree increases.
51) Define the free energy G and the equation of Gibbs - Helmotz:
It is born with desire to characterize a mathematical function that really is in a position to identifying if a process is spontaneous or less, in order to make that it must conglobare means you of entropy and entalpy, and being necessary a parity determine the proportions them is necessary to multiply the entropy for the temperature.
It is defined from the relation G = H - TS, and its variation to constant temperature DG = DH - T *DS characterizes a criterion in order to establish the spontaneità and the equilibrium of the reactions isoterme and isobars and is one measure of the useful job from these supplied.
52) Why it comes defined free energy:
Why it is the energy that really we have to disposition in how much we correspond to the thermal energy private total of the spold energy in order to produce order.
53) Criteria of equilibrium and spontaneità in function of the free energy DG:
If the transformation is isoterma and isobar:
If the transformation is spontaneous DG = DH - T *DS < 0
If the transformation is in equilibrio DG = DH - T *DS = 0
If the transformation is not spontanea DG = DH - T *DS > 0
54) When a reaction is spontaneous and therefore DG < 0:
From The DG = DH - T *DS
to) If the transformation is exothermic (DH < 0).
b) If the transformation is exothermic but the entropy diminishes
c) If the transformation is endothermic but the entropy increases.
It is therefore clearly that the spontaneità of a reaction is tied to the dominion or less of the entropico term on that entalpico
55) In the DG = DH - T *DS that unit has the product T *DS and consequently that unit must have DH:
T *DS is expressed automatically in calories, in such unit must also be expressed DH.
56) Enounce the relation that alloy the useful job and the free energy:
DG = -(L - P *DV) = - Lutile in the case of one transformation isobar and isoterma. If the transformation happens in reversible way the useful job it is maximum.
57) What is the free energy molar standard of G formationf°:
It is the variation of free energy DG that verification in the formation of a compound size, in its state standard, to leave from the elements, also they in you respect to you be standard.
58) How much is worth the free energy of one size of one any substance to the T temperature:
G = Gf° R * T * ln a where R = 1,99 cal/(mole*K)
where to it is the activity of the substance correspondent to the ideal concentration.
for ideal gases to = pressure
for not ideal gases to = f * p where f it is the activity coefficient
for solid and pure liquids the activity is unitary.
for one ideal solution to = concentration.
for a not ideal solution to = f * where f it is the activity coefficient.
It is observed that it is reported to a size and therefore if wharves are interested più, it is necessary to multiply G for their number.
59) As the value of the vapor tension of the liquid in equilibrium with the solid one can be gained:
It is prevailed that DG = 0 in how much the reaction must be in equilibrium, dopodichè is estimated DG° from some parameters of the problem and holding account that for solid and liquids G = G° extrapolates P from the G = Gf° R * T * ln to.