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q = energy transfer into system by heat flow -w = work done by system may be applied to the actual Calorimeter process, which is assumed to be adiabatic (q = 0). In the present experiment, w, which consists mainly of the work of stirring, can be neglected' and Eq. (2) then becomes AUc = 0 (3) Since the energy Change is independent of path, one has AU = AU, +] CdT (4) Since the temperature change is small, it is usually valid to consider C to be constant, so that the integral becomes equal to C(T2 - T1). One then obtains AUT1= -C(T2 - T1) (5) It may be observed that a temperature rise corresponds to a negative AUT1, that is, to a decrease in energy for the imagined isothermal process. The next step is to calculate AU-° from AUT1. Although the energy is not sensitive to changes in pressure, the correction to standard states, called the Washburn correction, may amount to several tenths of 1 Percent and is important in work of high accuracy.[2b,3b] The principal Washburn correction terms allow for the changes in U associated with (a) changes in pressure, (b) mixing of reactant gases and separating product gases, and (c) dissolving reactant gases in, and extracting product gases from, the water in the bomb. The standard enthalpy change AHT,° may then be calculated. The definition of H leads directly to AHT,° = AUT,° + A(PV) (6)

q = energy transfer into system by heat flow -w = work done by system may be applied to the actual Calorimeter process, which is assumed to be adiabatic (q = 0). In the present experiment, w, which consists mainly of the work of stirring, can be neglected' and Eq. (2) then becomes AUc = 0 (3) Since the energy Change is independent of path, one has AU = AU, +] CdT (4) Since the temperature change is small, it is usually valid to consider C to be constant, so that the integral becomes equal to C(T2 - T1). One then obtains AUT1= -C(T2 - T1) (5) It may be observed that a temperature rise corresponds to a negative AUT1, that is, to a decrease in energy for the imagined isothermal process. The next step is to calculate AU-° from AUT1. Although the energy is not sensitive to changes in pressure, the correction to standard states, called the Washburn correction, may amount to several tenths of 1 Percent and is important in work of high accuracy.[2b,3b] The principal Washburn correction terms allow for the changes in U associated with (a) changes in pressure, (b) mixing of reactant gases and separating product gases, and (c) dissolving reactant gases in, and extracting product gases from, the water in the bomb. The standard enthalpy change AHT,° may then be calculated. The definition of H leads directly to AHT,° = AUT,° + A(PV) (6)

Physical Chemistry
Physical Chemistry
2nd Edition
ISBN:9781133958437
Author:Ball, David W. (david Warren), BAER, Tomas
Publisher:Ball, David W. (david Warren), BAER, Tomas
Chapter2: The First Law Of Thermodynamics
Section: Chapter Questions
Problem 2.83E: Benzoic acid, C6H5COOH, is a common standard used in bomb calorimeters, which maintain a constant...
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Handwrite everything in the picture q = energy transfer into system by heat flow -w = work done by system may be applied to the actual Calorimeter process, which is assumed to be adiabatic (q = 0). In the present experiment, w, which consists mainly of the work of stirring, can be neglected' and Eq. (2) then becomes AUc = 0 (3) Since the energy Change is independent of path, one has AU = AU + J Co CdT (4) Since the temperature change is small, it is usually valid to consider C to be constant, so that the integral becomes equal to C(T2 - T1). One then obtains AUT1= -C(T2 - T1) (5) It may be observed that a temperature rise corresponds to a negative AUT1, that is, to a decrease in energy for the imagined isothermal process. The next step is to calculate AU,° from AUT1. Although the energy is not sensitive to changes in pressure, the correction to standard states, called the Washburn correction, may amount to several tenths of 1 Percent and is important in work of high accuracy.[2b,3b] The principal Washburn correction terms allow for the changes in U associated with (a) changes in pressure, (b) mixing of reactant gases and separating product gases, and (c) dissolving reactant gases in, and extracting product gases from, the water in the bomb. The standard enthalpy change AHT,° may then be calculated. The definition of H leads rectly to AHT,° = AUT,° + A(PV) (6) Since the standard enthalpy and energy for a real gas are so defined as to be the same, respectively, as the enthalpy and energy of the gas in the zero-pressure limit, the ideal-gas equation may be used to evaluate the contribution of gases to A(PV) in Eq. (6). The result is A(PV) = (nz-n;)RT (7) In the isothermal-jacket method, mentioned above, the stirring term is not neglected but rather is effectively eliminated along with the heat transfer by making a correction to the observed temperature rise [1-3a,4] where n2 = number of moles of gaseous products n; = number of moles of gaseous reactants %3D The contribution to A(PV) from the net change in PV of solids and liquids in going from reactants to products is generally negligible.
Transcribed Image Text:Handwrite everything in the picture q = energy transfer into system by heat flow -w = work done by system may be applied to the actual Calorimeter process, which is assumed to be adiabatic (q = 0). In the present experiment, w, which consists mainly of the work of stirring, can be neglected' and Eq. (2) then becomes AUc = 0 (3) Since the energy Change is independent of path, one has AU = AU + J Co CdT (4) Since the temperature change is small, it is usually valid to consider C to be constant, so that the integral becomes equal to C(T2 - T1). One then obtains AUT1= -C(T2 - T1) (5) It may be observed that a temperature rise corresponds to a negative AUT1, that is, to a decrease in energy for the imagined isothermal process. The next step is to calculate AU,° from AUT1. Although the energy is not sensitive to changes in pressure, the correction to standard states, called the Washburn correction, may amount to several tenths of 1 Percent and is important in work of high accuracy.[2b,3b] The principal Washburn correction terms allow for the changes in U associated with (a) changes in pressure, (b) mixing of reactant gases and separating product gases, and (c) dissolving reactant gases in, and extracting product gases from, the water in the bomb. The standard enthalpy change AHT,° may then be calculated. The definition of H leads rectly to AHT,° = AUT,° + A(PV) (6) Since the standard enthalpy and energy for a real gas are so defined as to be the same, respectively, as the enthalpy and energy of the gas in the zero-pressure limit, the ideal-gas equation may be used to evaluate the contribution of gases to A(PV) in Eq. (6). The result is A(PV) = (nz-n;)RT (7) In the isothermal-jacket method, mentioned above, the stirring term is not neglected but rather is effectively eliminated along with the heat transfer by making a correction to the observed temperature rise [1-3a,4] where n2 = number of moles of gaseous products n; = number of moles of gaseous reactants %3D The contribution to A(PV) from the net change in PV of solids and liquids in going from reactants to products is generally negligible.
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