Question

The combustion of one mole of benzene takes place at 298 K and 1 atm. After combustion, CO2(g) and H2O (1) are produced and 3267.0 kJ of heat is liberated. Calculate the standard enthalpy of formation, ΔfHΘof benzene. Standard enthalpies of formation of CO2(g) and H2O(l) are -393.5 kJ mol1and 285.83kJ mol1respectively.

Answer 1

Answer: Standard enthalpy of formation of benzene = 129.9 KJ/mol

Explanation: Enthalpy of the reaction is equal to the total sum of the standard enthalpies of the  formation of products minus the total sum of the standard enthalpies of formation of reactants. It is represented by $\Delta H_{reaction}$

Mathematically,

$\Delta H_{rxn}=\Delta H_{products}-\Delta H_{reactants}$

For the combustion of benzene:

$2C_6H_6(g)+15O_2(g)\rightarrow 12CO_2(g)+6H_2O(l)$

The standard enthalpy of the elements present in their standard state is always zero.

$\Delta H_{rxn}=[6(\Delta H_{H_2O})+12(\Delta H_{CO_2})]-[2(\Delta H_{C_6H_6})+15(\Delta H_{O_2})]$

Putting values in above equation, we get:

$3267.0 kJ=[6(285.83})+12(-393.5)]-[2(\Delta H_{C_6H_6})+15(0)]$

$\Delta H_f^0{C_6H_6$=129.9kJ/mol[/tex]

Answer 2

Answer:

nswer: Standard enthalpy of formation of benzene = 129.9 KJ/mol

Explanation: Enthalpy of the reaction is equal to the total sum of the standard enthalpies of the  formation of products minus the total sum of the standard enthalpies of formation of reactants. It is represented by \Delta H_{reaction}ΔHreaction

Mathematically,

\Delta H_{rxn}=\Delta H_{products}-\Delta H_{reactants}ΔHrxn=ΔHproducts−ΔHreactants

For the combustion of benzene:

2C_6H_6(g)+15O_2(g)\rightarrow 12CO_2(g)+6H_2O(l)2C6H6(g)+15O2(g)→12CO2(g)+6H2O(l)

The standard enthalpy of the elements present in their standard state is always zero.

\Delta H_{rxn}=[6(\Delta H_{H_2O})+12(\Delta H_{CO_2})]-[2(\Delta H_{C_6H_6})+15(\Delta H_{O_2})]ΔHrxn=[6(ΔHH2O)+12(ΔHCO2)]−[2(ΔHC6H6)+15(ΔHO2)]

Putting values in above equation, we get:

3267.0 kJ=[6(285.83})+12(-393.5)]-[2(\Delta H_{C_6H_6})+15(0)]

\Delta H_f^0{C_6H_6 =129.9kJ/mol[/tex]