Question

A 0.727-g sample of the sugar D-ribose (C5H10O5) was placed in a calorimeter and then ignited in the presence of excess oxygen. The temperature rose by 0.910 K. In a separate experiment in the same calorimeter, the combustion of 0.825 g of benzoic acid (Ucomb. = 3251 kJ/mol), gave a temperature rise of 1.904 K. Calculate following quantities. (a) calorimeter constant. (b) standard internal energy of combustion of D-ribose (c) standard enthalpy of combustion of D-ribose (d) standard enthalpy of formation of D-ribose.

Answer 1

gm weight of benzoic auid = 0.825 gm given) Molar mass of benzoic acid = 122112 gmmort u No. of motes of benzoic acid = am wt. mol-wt. I 0.625 = 0.00675 122:12 us internal energy su for 0.00675 moles of benzoic acid = -325140.00675= -2196KJ As we know AU-CAT where in calorimetes constant of Tistemp. i Calorimeter constant c- s0 AT=1.948,: C = - 3196-11:53 KJK4 1904 g wt of Dribore = 0.7279m (given) change in temp.(07) = 0.9106 Molar mass of D ribore=150.13 g No. of moles of Asibore 0.727 .. is 150.13 -0.00484 moles i standard internal energy of Combustion of a sibone

40 ? СХДТ moles - 11153x 0.910 0.00484 AU= -2167.830 KJMOVI Combustion of D-ribose Choost 5008 5 0 2t 5 H₂O change in moles ang= 5-5=0 SH = out ong RT i singo SHPOU= -2167.830 KJ m01-1 Standard enthepy of combustion = -2167.630 kJ mor! Standard enthalpy of formation of D-ribose AH = 5XAH CO2 +5XAMH20 - D M C H₂005