Q-w P since P=Pf=Pamb. Combining terms, U final+Pinal V(Initial + Initial Initial )=ecv initial In terms of the numbers of moles and the specific enthalpy this is ∑n1h1+Qcv=∑nlh (C.3.3) The enthalpy of CO2, at 25C and o 1 MPa, with reference to a base where the enthalpy of the elements is zero, is called the enthalpy of formation and denoted by h Values of the heat of formation for a number of substances are given in Table A. 9 in SB& vw. The enthalpies of the reactants and products for the formation of CO2 are ho =hc For one kmole: Qcv-Enhe=Hp=(n9)co--393, 522 kJ/kmole The enthalpy of Co2 in any other state(T, P)is given by h7-(19)a1+( 298K,0.1Mp→T,P These descriptions can be applied to any compound. For elements or compounds that exist more than one state at the reference conditions( for example, carbon exists as diamond and as graphite), we also need to specify the state Note that there is a minus sign for the heat of formation. The heat transfer is out of the control volume and is thus negative by our convention. This means that elements>hco,=-393,522 kJ Muddy points Is the enthalpy of formation equal to the heat transfer out of the combustion during the formation reaction?(MP 2C. 4) Are the enthalpies of H, and (monoatomic hydrogen) both zero at 298K?(MP 2C.5) 2C-4U final −Uinitial = Q − W = QCV − Pamb (Vfinal − Vinitial ), since P = Pf = Pamb . Combining terms, i U final + PfinalVfinal − (Uinitial + PinitialVinitial ) = QCV , or, = QCV H . final − Hinitial In terms of the numbers of moles and the specific enthalpy this is ∑nh + QCV = ∑n he (C.3.3) ii e R P The enthalpy of CO2, at 25o C and 0.1 MPa, with reference to a base where the enthalpy of the o elements is zero, is called the enthalpy of formation and denoted by hf . Values of the heat of formation for a number of substances are given in Table A.9 in SB&VW. The enthalpies of the reactants and products for the formation of CO2 are: = hC = 0 h hO2 o f For one kmole: Q , CV = ∑n he = HP = ( ) = −393 522 kJ/kmole. e P CO2 The enthalpy of CO2 in any other state (T,P)is given by hTP = ( ) + (∆h ) . , h0 f 298K,. 0 1 MPa 298K,. , 0 1 Mpa→T P These descriptions can be applied to any compound. For elements or compounds that exist in more than one state at the reference conditions (for example, carbon exists as diamond and as graphite), we also need to specify the state. Note that there is a minus sign for the heat of formation. The heat transfer is out of the control volume and is thus negative by our convention. This means that h , elements > h = −393 522 kJ . CO2 Muddy points Is the enthalpy of formation equal to the heat transfer out of the combustion during the formation reaction? (MP 2C.4) Are the enthalpies of H2 and H (monoatomic hydrogen) both zero at 298K? (MP 2C.5) 2C-4