# 7 - Thermodynamics and Thermochemistry Questions Answers

ΔHf  C2H4 = 12.5 kcal

Heat of atomization of C = 171 kcal

Heat of atomization of H = 52.1 kcal

Bond energy CH = 99.3 kcal .

What is C=C bond energy?

Joshi sir comment

2 heat of atomization of C + 4 heat of atomization of H - 4 bond energy of C-H - 1 bond energy of C=C = heat of formation of C2H4

2*171 + 4*52.1 - 4*99.3 - x = 12.5

solve

Integral enthalpy of soln of KCl , when 1 mole of it is dissolved in 20 mole water is +15.90kJ . When 1 mole of it is dissolved in 200mole water  dH =15.58kJ. Calculate enthalpy of hydratn or dilutn ??

ans is 2.68kJ

Joshi sir comment

Integral enthalpy

please check this word if wrong submit the correct question again

show that (du/dv)s=T-sdp

Joshi sir comment

question is incorrect

because (du/dv)s represents pressure and T is temperature

why heat of an ideal solution is taken as zero ?

Joshi sir comment

because in ideal solution there is no interaction between the two liquids present in the solution

The enthalpy of nuutralisation of  a strong acid HA and weaker acid HB by KOH are -13.7 and -12.7 kcal/eq. When one equivalent of KOH is added to a mixture containing 1 eq of HA amd HB ; the enthaply change was -13.5 kcal. In what ratio is thge base distributeed between HA and HB ?

Joshi sir comment

let x in HA and 1-x in HB

so according to the given condition -13.7x-12.7(1-x) = -13.5

solve

16 kg oxygen gas expands at STP isobarically to occupy double of its original volume. The work done during the process is 244 kcal. HOW????????

Joshi sir comment

W = PdV = nRdT = (16*1000/32)*(8.31/4.18)*273

now solve

the heat of formation of MgO, Al2O3, , And SiO2 Are -692, -1676, -911 kJ/mol . most stable oxide is

A) MgO

B) Al2O3

C) SiO2

D) can't be predicted