Physical Chemistry Chapter 5 The standard enthalpy change AHT for a chemical reaction △H0 ∑ T. (5.6)* Consider the reaction aA+bB→cC+dD Reactants aA+ bB Products cc +dD in their standard states in their standard states at T at T (2) Elements in their standard states at T
Consider the reaction aA＋b B → cC＋dD The standard enthalpy change for a chemical reaction o HT = i o i f T i o HT H , (5.6)* Reactants aA + bB in their standard states at T Products cC + dD in their standard states at T Elements in their standard states at T (1) (2) (3) Fig. 5.1 Physical Chemistry Chapter 5
Physical Chemistry Chapter 5 aA+bB→cC+dD △H=△H1=AH2+A3 AH2=aHr(A)+b△,Hr(B +)AH3=c△,H(O)+△H(D) AHx=-a△H(4)-b,HF7(B)+C△,H(C)+a△,HF(D) Reactants aa +bB Products cC + dD in their standard states in their standard states at T' at T Elements in their standard states at T' Fig. 5.1
a A＋b B →c C＋d D H H1 o T = = H2 + H3 ( ) ( ) H2 a H A b H B o f T o − = f T + ( ) ( ) H3 c H C d H D o f T o = f T + H a H (A) b H (B) c H (C) d H (D) o f T o f T o f T o f T o T = − − + + +) Reactants aA + bB in their standard states at T Products cC + dD in their standard states at T Elements in their standard states at T (1) (2) (3) Fig. 5.1 Physical Chemistry Chapter 5
Physical Chemistry Chapter 5 Determination of 4 Ho and 4, Ho Read page 144 Use calorimetry When a reaction is carried out in a calorimeter The heat gained/lost The heat lost/gained by the calorimeter and by the reacting system Its contents Changes in heat content are calculated using △H=m·c·△T
Determination of f Ho and r Ho • Read page 144 • Use calorimetry H = mcT When a reaction is carried out in a calorimeter The heat lost/gained by the reacting system The heat gained/lost by the calorimeter and its contents = Changes in heat content are calculated using Physical Chemistry Chapter 5
Physical Chemistry Chapter 5 Enthalpies of combustion are measured in a 一 bomb calorimeter Ignition wires electrical Thermometer heater Stirrer ----- 耕 Adiabatic wall O2(g) Sample pellet Fig. 5.4
Enthalpies of combustion are measured in a bomb calorimeter. H2O O2 (g) Sample pellet Stirrer Electrical heater Thermometer Ignition wires Fig. 5.4 Adiabatic wall Physical Chemistry Chapter 5
Physical Chemistry Chapter 5 T thermochemistry The study of the heat produced or required by chemical reactions Calorimetetry Heat produced /adsorbed by a reaction 9=40 q=4H const (const
Thermochemistry The study of the heat produced or required by chemical reactions Calorimetetry Heat produced /adsorbed by a reaction q = U (const. V) q = H (const. P) Physical Chemistry Chapter 5