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The standard enthalpy of the formation of NH3 is -46.0 kJ mol-1. If the enthalpy of the formation of H2 from its atoms is -436 kJ mol-1 and that of N2 is -712 kJ mol-1, the average bond enthalpy of N-H bond in NH3 is:

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Important Questions on Thermodynamics

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On the basis of the following thermochemical data:

ΔHf°Haq+=0

H2O(l)H+(aq)+OH-(aq);  ΔH°=57.32kJH2(g)+12O2(g)H2O(l);  ΔH°=-286.20kJ

The value of the enthalpy of formation of OH- ions at 25°C is:

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The equilibrium constant for the reaction A+BC+D is 10ΔG° for the reaction at 300 K is
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One mole of an ideal gas expands reversibly and isothermally at 300 K from 5dm3 to 50dm3. The work done by the gas for the process is equal to
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The entropy change for an adiabatic reversible process is
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Two moles of an ideal monoatomic gas are allowed to expand adiabatically and reversibly from 300 K to 200 K. The work done by the system is CV=12.5 J K-1 mol-1
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Based on the following thermochemical equation:

H2O(g) + C (s) =CO (g) + H2 (g)     ;     H = 131 kJ

CO(g) +12 O2 (g) =CO2g     ;     H =- 282 kJ

H2(g) +12 O2 (g) =H2Og       ;     H = -242 kJ

C(s)+O2(g)=CO2(g)  ; ΔH=-x kJ

The value of x will be:

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Consider the following reactions occurring in an automobile, C8H18(g)+252O2(g)8CO2(g)+9H2O(g)

The sign of ΔH, ΔS and ΔG respectively would be,

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Given that

C+O2CO2; H=-x kJ

2CO+O22CO2; ΔH=-y kJ

The enthalpy of formation of CO will be