ThermochemistryHard
Question
How much energy is released when 6 moles of octane is burnt in air ? Given ᐃHfo for CO2(g), H2O(g) and C8H18(1) respectively are - 490, - 240 and + 160J/mol
Options
A.-6.2 kJ
B.- 37.4kJ
C.- 35.5kJ
D.- 20.0kJ
Solution
C + O2 = CO2 ᐃH = - 490 (i)
H2 +
O2 = H2O ᐃH = - 240 (ii)
8C + 9H2 = C8H18 ᐃH = + 160 (iii)
2C8H18 + 25O2 = 16CO2 + 18H2O
The required reaction can be obtained by
2 × (iii) - 16(i) - 18(ii)
16C + 18H2 - 16C - 16O2 - 18H2 - 9O2
= 2C8H18 - 16CO2 - 18H2O
or - 25O2 = 2C8H18 - 16CO2 - 18H2O 2C8H18 + 25O2 = 16CO2 + 18H2O
[ᐃH = 2 × 160 - 16 × - 490 - 18 × - 240]
ᐃH = - 11840J = - 11.840 kJ for 2 moles of
Octance. Energy releced for 6 moles of
Octance. = - 11840 × 3 = - 35.5kJ
H2 +
O2 = H2O ᐃH = - 240 (ii)8C + 9H2 = C8H18 ᐃH = + 160 (iii)
2C8H18 + 25O2 = 16CO2 + 18H2O
The required reaction can be obtained by
2 × (iii) - 16(i) - 18(ii)
16C + 18H2 - 16C - 16O2 - 18H2 - 9O2
= 2C8H18 - 16CO2 - 18H2O
or - 25O2 = 2C8H18 - 16CO2 - 18H2O 2C8H18 + 25O2 = 16CO2 + 18H2O
[ᐃH = 2 × 160 - 16 × - 490 - 18 × - 240]
ᐃH = - 11840J = - 11.840 kJ for 2 moles of
Octance. Energy releced for 6 moles of
Octance. = - 11840 × 3 = - 35.5kJ
Create a free account to view solution
View Solution FreeMore Thermochemistry Questions
The standard enthalpy of formation of NH3 is - 46.0 kJ mol-1. If the enthalpy of formation of H2 from its atoms is - 436...CsF(S) → Cs+(aq) + F-(aq) ᐃH = - 40 kJ mol- If lattic energy of CsF is 750 kJ mol- . Then the summation of h...Enthalpy of formation of HF and HCl are - 161 kJ and - 92 kJ respectively. Which of thefollowing statements is incorrect...The above p-v diagram represents the thermodynamic cycle of an engine, operating with an ideal monoatomic gas. The amoun...Given that :-CH4(g) + 300 kJ → C(g) + 4H(g)C2H6(g) + 620 kJ → 2C(g) + 6H(g)The value of C - C bond energy is...