Thermochemistry: enthalpies of formation, combustion, bond enthalpy, Hess's law

38 questions on Thermochemistry: enthalpies of formation, combustion, bond enthalpy, Hess's law from the Thermodynamics and Thermochemistry chapter: 8 NEET level, 16 JEE Main, 14 JEE Advanced. Each one opens with its answer and solution.

• Which of the following has a standard enthalpy of formation equal to zero at 298 K? NEET level
• Hess's law of constant heat summation is a direct consequence of the fact that enthalpy is NEET level
• Using average bond enthalpies (H-H = 436, Cl-Cl = 243, H-Cl = 431 kJ mol^-1), the enthalpy change of H2(g) + Cl2(g) -> 2HCl(g) is NEET level
• For which of the following gas-phase reactions (ideal gases) is Delta H = Delta U? NEET level
• Using Delta_fH deg/kJ mol^-1: C3H8(g) = -103.8, CO2(g) = -393.5, H2O(l) = -285.8, calculate the standard enthalpy of combustion of propane, C3H8(g) + 5O2(g) -> ... JEE Main level
• Using average bond enthalpies in kJ mol^-1 (C=C = 614, C-C = 348, Br-Br = 193, C-Br = 276), estimate the enthalpy change in kJ mol^-1 for CH2=CH2(g) + Br2(g) ->... JEE Main level
• Given S(s) + O2(g) -> SO2(g), Delta H = -296.8 kJ, and SO2(g) + 1/2 O2(g) -> SO3(g), Delta H = -98.9 kJ, the enthalpy change for S(s) + 3/2 O2(g) -> SO3(g) is JEE Main level
• The standard enthalpy of combustion of liquid benzene, C6H6(l) + 15/2 O2(g) -> 6CO2(g) + 3H2O(l), is -3267 kJ mol^-1 at 298 K. Find Delta U for the reaction in ... JEE Main level
• The enthalpy of combustion of ethene is -1411 kJ mol^-1. The heat released on complete combustion of 5.6 g of ethene (M = 28 g mol^-1) is JEE Main level
• The enthalpies of combustion of C2H6(g), graphite and H2(g) are -1560, -393.5 and -285.8 kJ mol^-1 respectively (H2O formed as liquid). The standard enthalpy of... JEE Main level
• A bomb calorimeter has a heat capacity of 20.0 kJ K^-1 (including contents). Burning 1.20 g of graphite in excess oxygen (C + O2 -> CO2, Delta_cH = -393.5 kJ mo... JEE Main level
• 100 mL of 1.00 M HCl is mixed with 100 mL of 1.00 M NaOH in an insulated cup. For neutralisation Delta H = -57.1 kJ mol^-1. Assuming density 1.00 g mL^-1, speci... JEE Main level
• Given Delta_fH deg(CH4(g)) = -74.8, enthalpy of sublimation of graphite = 717, and H-H bond enthalpy = 436 (all in kJ mol^-1), estimate the average C-H bond ent... JEE Advanced level
• Given Delta_fH deg/kJ mol^-1: C2H5OH(l) = -277.7, CO2(g) = -393.5, H2O(l) = -285.8. Select the correct statement(s). JEE Advanced level
• A gaseous mixture of CH4 and H2 totalling 1.00 mol releases 520 kJ of heat on complete combustion to CO2(g) and H2O(l). The enthalpies of combustion are -890 kJ... JEE Advanced level
• For NaCl(s): Delta_fH deg = -411, sublimation of Na(s) = +108, ionisation enthalpy of Na(g) = +496, Cl-Cl bond enthalpy = +242, electron gain enthalpy of Cl(g) ... JEE Advanced level
• Reactions are carried out at 298 K with all gases ideal (R = 8.314 J mol^-1K^-1). Select the correct statement(s). JEE Advanced level
• For N2(g) + 3H2(g) -> 2NH3(g), Delta H deg_298 = -92.2 kJ. Molar heat capacities C_p/J mol^-1K^-1: N2 = 29.1, H2 = 28.8, NH3 = 35.1 (temperature independent). T... JEE Advanced level
• Data in kJ mol^-1: Delta_cH(graphite) = -393.5; Delta_cH(CO) = -283.0; Delta_cH(H2) = -285.8 (to liquid water); Delta_vapH(H2O) = +44.0. For the water-gas shift... JEE Advanced level
• Which of the following has a non-zero standard enthalpy of formation at 298 K? NEET level
• Hess's law of constant heat summation states that the enthalpy change of a reaction NEET level
• The standard enthalpy of complete combustion of a hydrocarbon at 298 K is NEET level
• The H-H bond enthalpy is 436 kJ mol^-1. What is Delta H for 2H(g) -> H2(g)? NEET level
• Using Delta_fH deg(C2H4(g))=+52.3, Delta_fH deg(CO2(g))=-393.5 and Delta_fH deg(H2O(l))=-285.8 kJ mol^-1, find Delta H deg for C2H4(g) + 3O2(g) -> 2CO2(g) + 2H2... JEE Main level
• Estimate Delta H for CH4(g) + Cl2(g) -> CH3Cl(g) + HCl(g) using bond enthalpies in kJ mol^-1: C-H=414, Cl-Cl=243, C-Cl=339, H-Cl=431. JEE Main level
• The standard enthalpies of combustion (to CO2(g) and H2O(l)) are -1300 for C2H2(g), -1411 for C2H4(g) and -286 for H2(g), all in kJ mol^-1. Calculate Delta H fo... JEE Main level
• For N2O4(g) -> 2NO2(g) at 298 K, Delta H=+57.2 kJ per mole of N2O4. Taking R=8.314 J mol^-1K^-1, calculate Delta U in kJ mol^-1 (two decimals). JEE Main level
• 0.46 g of liquid ethanol (M=46 g mol^-1) is burnt completely in a bomb calorimeter whose heat capacity (including contents) is 10.4 kJ K^-1; the temperature ris... JEE Main level
• Select the correct statement(s) about standard enthalpy changes at 298 K. JEE Main level
• 100 mL of 0.5 M HCl is mixed with 100 mL of 0.5 M NaOH in an insulated vessel. Take Delta H_neut=-57.1 kJ mol^-1, total mass of solution 200 g and specific heat... JEE Main level
• For CaCO3(s) -> CaO(s) + CO2(g), Delta H_298=+178.0 kJ. Heat capacities (in J mol^-1K^-1, assumed constant): CaCO3=83.5, CaO=42.0, CO2=37.1. Estimate Delta H at... JEE Main level
• Estimate Delta_fH of C2H6(g) from the following data in kJ mol^-1: enthalpy of sublimation of carbon (graphite -> C(g)) =717; bond enthalpies H-H=436, C-H=414, ... JEE Advanced level
• The standard enthalpies of combustion at 298 K are -393.5 for graphite, -285.8 for H2(g) and -2220.0 kJ mol^-1 for C3H8(g) (products CO2(g) and H2O(l)). The sta... JEE Advanced level
• Given (in kJ mol^-1): C(gr) + O2(g) -> CO2(g), Delta H=-393.5; CO(g) + 1/2 O2(g) -> CO2(g), Delta H=-283.0; H2(g) + 1/2 O2(g) -> H2O(l), Delta H=-285.8; H2O(l) ... JEE Advanced level
• For a salt MX(s) the lattice enthalpy (energy needed to separate the solid into gaseous ions) is +758 kJ mol^-1, and the hydration enthalpies of the gaseous ion... JEE Advanced level
• For N2(g) + 3H2(g) -> 2NH3(g), Delta H_298=-92.2 kJ. Assume constant molar heat capacities C_P (in J mol^-1K^-1): N2=29.1, H2=28.8, NH3=35.1, and R=8.314 J mol^... JEE Advanced level
• A mixture of CH4(g) and H2(g) containing 0.50 mol in total is burnt completely (to CO2(g) and H2O(l)) and releases 300 kJ of heat. The standard enthalpies of co... JEE Advanced level
• Given Delta_fH deg(H2O(g))=-242 kJ mol^-1, bond enthalpy of H-H=436 and of O=O=498 kJ mol^-1. Select the correct statement(s). JEE Advanced level