--%>

Define thermal energy, How to calculate thermal energy?

The thermal part of the internal energy and the enthalpy of an ideal gas can be given a molecular level explanation.


All the earlier development of internal energy and enthalpy has been "thermodynamic". We have made no use of the molecular level understanding of energy that we obtained in the energy crisis. There you recall, we found that we could calculate the thermal energy contribution U- U0 for molecularity sample systems such as ideal gases. Now this thermal energy will be released to the thermodynamic internal energy and enthalpy.

The energy of a system when only the lowest available energy levels are occupied is derived on the concept of energy level. This is the energy that the system would have if the temperature were occupied. This is the energy were lowered to absolute zero and the system did not change its physical form. The thermal energy U- U0 is the additional process energy that the system would acquire if the temperature were raised from this hypothesis zero temperature form and the particles distributed thermodynamical energy themselves throughout the energy levels.

Thermal enthalpy H - H0: the general relation between enthalpy and internal energy is H - H0

For some liquids and solids at all ordinary pressures, the change in the PV term is small compared to changes in the H and U terms. As a result, at any temperature the enthalpy and internal energy are effectively equal. Thus H = u, H0 = U0, and H - H0 = U - U0. For standard state thermal enthalpies and internal energies we have 

H0T - H00 + U0T  - U00  [liquid or solid]

For gases, ideal behavior allows the PV term for a sample containing 1 mol of gas molecules to be equated to RT. When only the lowest energy states are compared, as occurs at the thermal energy results we can be converted to enthalpies by addition of RT. For standard state thermal enthalpies and internal energies we have various values for the thermal enthalpy at T = 298 K and for several other temperatures for some elements and compounds are included in this phenomenon.

Instance: nitrogen oxide, NO, forms from oxygen and nitrogen in internal combustion engines. (This reaction proceeds to a sufficient extent at the high temperatures of the engine for NO to be prodcue4d in amounts that cause serious pollution problems. Part of understanding the formation and decomposition of NO is based on the enthalpy change for the reaction at high temperatures, where NO is formed and at lower temperatures where it breaks up to N2 andO2.)

Calculate ΔH°0 and ΔH°2000 for the reaction in which NO is formed from its elements.

Answer: we begin by obtaining ΔH°0 as:

1070_molecular thermal energy.png             

Now at any temperature, such as 2000K, which is representative of high temperatures at which calorimetric methods are not applicable, we have for N2, for example, 2000 - H°0 = (H°2000 - H°298) + (H°298 - H°0) = 56.14 - (- 8.67) = 64.81 kJ. Then:

29_molecular thermal energy1.png                     

These values give:

ΔH°2000 = ΔH°0 + Δ(H°2000 - H°0)

= 179.50 + 1.41

=180.91 kJ


Notice that ΔH for the reaction can be deduced for any temperature at which the thermal energies of the reactants and the products can be calculated.

   Related Questions in Chemistry

  • Q : Normality how 0.5N HCL is prepared for

    how 0.5N HCL is prepared for 10 littre solution

  • Q : Define thermal energy The thermal part

    The thermal part of the internal energy and the enthalpy of an ideal gas can be given a molecular level explanation. All the earlier development of internal energy and enthalpy has been "thermodynamic". We have made no use o

  • Q : Problem on mole fraction of glucose

    Provide solution of this question. While 1.80gm glucose dissolve in 90 of H2O , the mole fraction of glucose is: (a) 0.00399 (b) 0.00199 (c) 0.0199 (d) 0.998

  • Q : Vapour pressure of benzene Give me

    Give me answer of this question. The vapour pressure of benzene at a certain temperature is 640mm of Hg. A non-volatile and non-electrolyte solid weighing 2.175g is added to 39.08g of benzene. The vapour pressure of the solution is 600,mm of Hg . What is the mo

  • Q : Significance of the organic chemistry

    Describe some of the significance of the organic chemistry in brief?

  • Q : Calculating Formulae Superphosphate has

    Superphosphate has the formula CaH4(PO4)2 H2O, what is the calculation to get the percentage of Phosphorus, I need to show the calculation. I know it is 30.9737622 u in weight and 2 atoms of the formula, but not sure how to work the calculation backwards.

  • Q : Precipitation problem On passing H 2 S 

    On passing H2S  gas through a solution of Cu+ and Zn+2 ions, CuS is precipitated first because: (i) Solubility product of CuS is equal to the ionic product of ZnS (ii) Solubility product of CuS is equal to the solubility product o

  • Q : Problem on molarity-normality-molality

    Can someone please help me in getting through this problem. The solution ofAl2(SO4)3 d = 1.253gm/m comprise 22% salt by weight. The molarity, normality and molality of the solution is: (1) 0.805 M, 4.83 N, 0.825 M (2)

  • Q : Numerical The volume of water to be

    The volume of water to be added to 100cm3 of 0.5 N N H2SO4 to get decinormal concentration is : (a) 400 cm3 (b) 500cm3 (c) 450cm3 (d)100cm3

  • Q : Procedure for separating the components

    Briefly describe the procedure for separating the components of the gun-powder?