In the name of Allah

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1 In the name of Allah

2 Physical chemistry- 2 nd state semester 1 Petroleum and petrochemical engineering. Lecture No. 5,6 Thermodynamics Assistance prof. Dr. Luma Majeed Ahmed lumamajeed2013@gmail.com, luma.ahmed@uokerbala.edu.iq

3 The First Law of Thermodynamics The First Law of Thermodynamics is a special case of the Law of Conservation of Energy. It is a special cases when only the internal energy changes and the only energy transfers are by heat and work. The First Law of Thermodynamics states that ΔE int = Q + W Quantit y Q Definition Meaning of + sign Meaning of sign Energy transferred by heat flow Heat flow into the system W Work Work done on the system DU (ΔE int ) Internal energy change Internal energy increase Heat flow out of the system Work done by the system Internal energy decrease

4 DU = U final - U initial = q w DU = a state function dependent on the current properties only. State function is a property that is independent of how a sample is prepared, completely differential,single valued Properties that relate to the preparation of the state are called path functions DU is path independent while q and w are not state functions because they can be converted from one form of energy to the other. (excluding other forms of energy, e.g. electrical, light and nuclear energy, from this discussion.)

5 Exact and Inexact Differentials

9 The Concept of Work Changes in Volume Cause Work: Work is performed when air contracts F F Work is done when an object is moved against an opposing force W= -P surr.δv

10 Work: Type of work dw comments units Volume Expansion -p surr dv P surr is the external pressure dv is the change in volume Pa m 3 Surface expansion γda γ is the surface tension da is the change in area Mechanical fdl f is the tension dl is the change of length Electrical Фdq Ф is the electric potential dq is the change in charge Gravitational mgdh m is the mass gdh is the change in height multiplied by gravitation acceleration Thermal CdT C is the heat capacity dt is the change of Temperature Chemical μdn μ is the chemical potential dn is the change in no. of mole N.m -1 M 2 N M V C kg m 2 s -2 K J mol -1 g -1 J mol -1 mol

11 Drive the Volume Expansion work

13 Heat is defined as the transfer of energy across the boundary of a system due to a temperature difference between the system and its surroundings. Units of Heat Historically, the calorie was the unit used for heat. One calorie is the amount of energy transfer necessary to raise the temperature of 1 g of water from 14.5 o C to 15.5 o C.The Calorie used for food is actually 1 kilocalorie. British Thermal Unit One BTU is the amount of energy transfer necessary to raise the temperature of 1 lb of water from 63 o F to 64 o F. The standard in the text is to use Joules.

14 Thermal Capacities (Specific Heats) Assume: A small quantity of heat (dq) is given to a parcel The parcel responds by experiencing a small temperature increase (dt) Specific Heat (c): c dq dt Two Types of Specific Heats: Depends on how the material changes as it receives the heat Constant Volume: c v du dt constant volume Parcel experiences no change in volume Constant Pressure: c p dh dt constant pressure Parcel experiences no change in pressure Thermodynamics M. D. Eastin

15 Thermal Capacities (Specific Heats) Specific Heat at Constant Volume: Starting with: c v dq dt constant volume If the volume is constant (dv = 0), we can re-write the first law as: du pdv dq du dq And substitute this into our specific heat equation as du c v or du c v dt dt Thermodynamics M. D. Eastin

16 Thermal Capacities (Specific Heats) Specific Heat at Constant Volume: Since the internal energy is a state variable and does not depend on past states or how state changes occur, we can define changes in internal energy as: DU T T 1 2 c v dt Also, if we substitute our specific heat equation into the first law: du c v dt du pdv dq We can obtain an alternative form of the First Law of Thermodynamics: dq cvdt pdv Thermodynamics M. D. Eastin

17 Equipartition of Energy The internal energy of non-monatomic molecules includes also vibrational and rotational energies besides the translational energy. Each degree of freedom has associated with 1 it an energy of per molecules. 2 k BT

18 E int nc V T Monatomic Gases 3 translational degrees of freedom: E int 3 2 k BT nn A 3 2 nrt C V 1 n de int dt 3 2 R

19 Polyatomic Gases E int nc V T degrees of freedom: E int = E trans. + E rot. + E vibr. E int. = 3 RT + 2 RT+ (3N-5)RT 2 2 Cv = 3 R + 2 R+ (3N-5)R 2 2 Linear gas molecular E int. = 3 RT + 3 RT+ (3N-6)RT 2 2 Cv = 3 R + 3 R+ (3N-6)R 2 2 Non-Linear gas molecular

James Prescott Joule 1818 1889 British physicist Largely self-educated Some formal education from John Dalton Research led

20 James Prescott Joule British physicist Largely self-educated Some formal education from John Dalton Research led to establishment of the principle of conservation of energy Determined the amount of work needed to produce one unit of energy

27 Heat of Formation (ΔH f ) It is defined as the increase of enthalpy when 1 mole of compound is formed from it is elements. It is denoted by H f o Heat of Combustion (ΔH comb ) It is defined as the enthalpy change accompanying the complete combustion of 1 mole of compound.organic compounds containing C, H, O can be burnt in oxygen to form CO 2 + H 2 O, this enthalpy used to know the heat of combustion of fuel as liquid or gas states. Heat of fusion( ΔH fus ) : It is enthalpy change that accompanies the melting, or fusion, of 1 mol of a substance. Heat of Solution (ΔH soln ) It is defined as the heat of reaction for dissolving 1 mole of solute in n moles From solvent. It is known as integral heat of solution. There are two types: a- Integral heat of solution: b- Differential heat of solution: It is defined as the heat of reaction for dissolving 1 mole of solute in very high amount of solvent, that will produce a very slight change in temperature (i.e, T 2 T 1 ).

Differential Heat of solution Integral Heat of solution n of solvent This figure shows the ability to change the integral heat of

28 Note: The integral heat of solution can be transferred to differential heat of solution by increasing the amount of solvent, that will lead to equal the initial temperature and final temperature. Differential Heat of solution Integral Heat of solution n of solvent This figure shows the ability to change the integral heat of solution to differential heat of solution by increasing to the amount of solvent, when the value of heat of solution is fixed n of H 2 O NaCl NaOH HCl This reaction is occurred in stomch

Latent heat Heat that cannot be detected because there is no change in temperature of the system. e.g. The heat that is used to melt ice or to evaporate water is latent heat.

29 Latent heat Heat that cannot be detected because there is no change in temperature of the system. e.g. The heat that is used to melt ice or to evaporate water is latent heat. There are two forms of latent heat: 1- Heat of fusion : The heat that must be absorbed to melt a mole of a solid, like melting ice to liquid water 2- Heat of vaporization : The heat that must be absorbed to boil a mole of a liquid, like boiling liquid water to steam

30 Enthalpy of atomization The enthalpy change in converting one mole of a substance into its constituent atoms in gaseous states is called the enthalpy of atomization or heat of atomization of that substance. (1) Enthalpy of atomization of a diatomic molecule. The enthalpy of atomization of a diatomic molecule is equal to its enthalpy of dissociation ΔdH Thus: (2) Enthalpy of atomization of a polyatomic molecule The enthalpy of atomization of a polyatomic molecule of a compound is equal to the enthalpy change to breaking all the covalent bonds so that gaseous constituent atoms are produced. The enthalpy of atomization of CH 4 is 1664 kj mol 1. which is equal to the enthalpy change associated with the breaking of the four C H bonds per mole of CH 4 molecules. (3) The enthalpy of atomization of a solid element is equal to its heat of sublimation.

17.4 Calculating Heats Essential Understanding Heats of reaction can be calculated when it is difficult or

17.4 Calculating Heats Essential Understanding Heats of reaction can be calculated when it is difficult or 17.4 Calculating Heats of Reaction Essential Understanding Heats of reaction can be calculated when it is difficult or impossible to measure them directly. Lesson Summary Hess s Law Hess s law provides