Free NEET Chemistry multiple-choice questions on Thermochemistry. Attempt each question and reveal the answer with a full explanation.
The standard enthalpy of formation of H +(aq) at 298 , K is defined as: 0 , kJ , mol -1 -286 , kJ , mol -1 +13.7 , kJ , mol -1 -57.3 , kJ , mol -1 The enthalpy of formation of AgCl from its elements cannot be directly determined. It is calculated using a cycle known as: Born-Haber cycle Carnot cycle Hess cycle Nitrogen cycle For the combustion of methane at 298 , K , n g is: -2 0 -1 2 The heat of formation of CO 2(g) is -393.5 , kJ , mol -1 . This value is equal to: The heat of combustion of graphite The heat of combustion of diamond The heat of combustion of CO(g) The heat of sublimation of carbon The enthalpy of formation of all elements in their standard states is conventionally taken as: Zero Positive Negative Infinite Identify the correct standard state for Sulfur at 298 K and 1 atm pressure. Rhombic Sulfur Monoclinic Sulfur Plastic Sulfur Colloidal Sulfur The molar heat of combustion of C 2H 2(g) is -1300 kJ/mol . If 0.5 mole of C 2H 2 is burnt in excess oxygen, the amount of heat released is: 650 kJ 1300 kJ 2600 kJ 325 kJ Calculate the change in enthalpy ( H ) for the reaction 2H 2(g) + O 2(g) 2H 2O(l) given the enthalpies of formation: f H[H 2O(l)] = -285.8 kJ/mol . -571.6 kJ -285.8 kJ +571.6 kJ 0 kJ The Born-Haber cycle is used to determine: Lattice energy Bond energy Electronegativity Ionization energy only Consider the following reactions: (i) H+ (aq) + OH- (aq) = H2O (l) , H = -X 1 kJ mol -1 (ii) H2 (g) + 1 2 O2 (g) = H2O(l) , H = -X 2 kJ mol -1 (iii) CO2 (g) + H2 (g) = CO (g) + H2O , H = -X 3 kJ mol -1 (iv) C2H2 (g) + 5 2 O2 (g) = 2CO2 (g) + H2O(l) , H = -X 4 kJ mol -1 Enthalpy of formation of H2O (l) is +X 3 kJ mol -1 -X 4 kJ mol -1 +X 1 kJ mol -1 -X 2 kJ mol -1 The energy absorbed by each molecule ( A 2) of a substance is 4.4 10 -19 J and bond energy per molecule is 4.0 10 -19 J . The kinetic energy of the molecule per atom will be : 4.0 10 -20 J 2.0 10 -20 J 2.2 10 -19 J 4 10 -19 J The enthalpy of formation of monoclinic sulfur is +0.33 , kJ , mol -1 relative to rhombic sulfur. This implies that: Rhombic sulfur is the standard state of sulfur. Monoclinic sulfur is more stable than rhombic sulfur. The conversion of rhombic to monoclinic sulfur is exothermic. Monoclinic sulfur is the standard state of sulfur. C(s) + 2H2(g) -> CH4(g) ; H = -74.8 kJ mol -1 . Which of the following diagrams gives an accurate representation of the above reaction? [R reactants; P products] The heat of combustion of carbon to CO 2 is -393.5 , kJ/mol . The heat released upon the formation of 35.2 , g of CO 2 from carbon and oxygen gas is: 314.8 , kJ 393.5 , kJ 630 , kJ 3.15 , kJ The heat of neutralization of a strong acid and a strong base is -57.1 , kJ , eq -1 . If the heat of neutralization of HCN by NaOH is -12.1 , kJ , eq -1 , the heat of ionization of HCN is: 45.0 , kJ , mol -1 -45.0 , kJ , mol -1 69.2 , kJ , mol -1 12.1 , kJ , mol -1 The bond dissociation energies of H 2(g) , Cl 2(g) and HCl(g) are 434 , 242 and 431 , kJ , mol -1 respectively. Enthalpy of formation of HCl(g) is: -93 , kJ , mol -1 +245 , kJ , mol -1 -245 , kJ , mol -1 +93 , kJ , mol -1 The heat of combustion of carbon to CO 2 is -393.5 , kJ/mol . The heat released upon formation of 35.2 , g of CO 2 from carbon and oxygen gas is: 314.8 , kJ 31.5 , kJ 630 , kJ 3.15 , kJ The enthalpy of neutralization of HCl and NaOH is -57.3 kJ mol -1 . The heat evolved at constant pressure when 0.5 mol of H 2SO 4 react with 1 mol of NaOH is: 57.3 kJ 28.65 kJ 114.6 kJ 0 kJ For which of the following elements is the standard enthalpy of formation ( Δ f H ⊖ ) NOT zero at 298 K ? Br 2(g) Cl 2(g) O 2(g) Hg(l) Given the following thermochemical equations: (i) S(s) + O 2(g) ightarrow SO 2(g), ΔH = -297 kJ ; (ii) 2SO 2(g) + O 2(g) ightarrow 2SO 3(g), ΔH = -198 kJ . The enthalpy of formation of SO 3(g) is: -396 kJ -495 kJ -594 kJ -297 kJ Given that the lattice energy of NaCl(s) is 788 , kJ , mol -1 and the enthalpy of hydration of Na +(g) and Cl -(g) are -406 , kJ , mol -1 and -378 , kJ , mol -1 respectively, the enthalpy of solution of NaCl(s) is: 4 , kJ , mol -1 -4 , kJ , mol -1 788 , kJ , mol -1 -784 , kJ , mol -1 The heat of neutralization of HCl by NaOH is -57.3 , kJ , mol -1 and with NH 4OH is -51.4 , kJ , mol -1 . The enthalpy of ionization of NH 4OH is: 5.9 , kJ , mol -1 -5.9 , kJ , mol -1 108.7 , kJ , mol -1 -108.7 , kJ , mol -1 The enthalpy of atomization of CH 4(g) is 1665 kJ mol -1 . What is the bond enthalpy of the C-H bond? 416.25 kJ mol -1 832.5 kJ mol -1 1665 kJ mol -1 555 kJ mol -1 A sample of gas expands from V 1 to V 2 . The amount of work done by the gas is greatest when the expansion is: Isothermal reversible Isothermal irreversible Adiabatic reversible Adiabatic irreversible In the Born-Haber cycle for the formation of MgO(s) , which of the following steps is endothermic? Sublimation of Mg(s) Formation of O 2- (g) from O -(g) Ionization of Mg(g) to Mg 2+ (g) All of the above In a bomb calorimeter, the combustion of 0.5 , g of a fuel resulted in a temperature rise of 2 , K . If the heat capacity of the calorimeter is 10 , kJ/K , the internal energy of combustion ( U ) per gram of fuel is: -40 , kJ/g -20 , kJ/g -10 , kJ/g -5 , kJ/g The reference state (standard state) of Phosphorus at 298 , K is: P 4 (white phosphorus) P (red phosphorus) P (black phosphorus) P 2 (gaseous phosphorus) The heat of formation of CO 2(g) is -393.5 , kJ , mol -1 and that of CO(g) is -110.5 , kJ , mol -1 . The heat of combustion of CO(g) is: -283.0 , kJ , mol -1 -504.0 , kJ , mol -1 +283.0 , kJ , mol -1 -393.5 , kJ , mol -1 The bond energies of H-H , Br-Br , and H-Br are 433 , 192 , and 364 , kJ , mol -1 respectively. The H for the reaction H 2(g) + Br 2(g) 2HBr(g) is: -103 , kJ +103 , kJ -261 , kJ +261 , kJ If the heat of combustion of Carbon (graphite) to CO 2(g) is H 1 and the heat of combustion of Carbon (diamond) to CO 2(g) is H 2 , then the enthalpy of transition from graphite to diamond is: H 1 - H 2 H 2 - H 1 H 1 + H 2 2( H 1 - H 2) The enthalpy of solution of anhydrous CuSO 4 is -66.5 , kJ , mol -1 and that of CuSO 4 5H 2O is 11.7 , kJ , mol -1 . The enthalpy of hydration of CuSO 4 is: -78.2 , kJ , mol -1 -54.8 , kJ , mol -1 78.2 , kJ , mol -1 54.8 , kJ , mol -1 The heat of combustion of H 2(g) is -286 , kJ , mol -1 and that of CH 4(g) is -890 , kJ , mol -1 . Which of the following is a better fuel in terms of heat per gram? H 2 CH 4 Both are equal Cannot be determined Given the enthalpies of combustion of ethene ( C 2H 4 ) and ethane ( C 2H 6 ) are -1411 and -1560 , kJ , mol -1 respectively, and the enthalpy of combustion of H 2 is -286 , kJ , mol -1 , the enthalpy of hydrogenation of ethene is: -137 , kJ , mol -1 137 , kJ , mol -1 -435 , kJ , mol -1 435 , kJ , mol -1 Which of the following is the standard state of Carbon? Graphite Diamond Fullerene Coal The enthalpy of combustion of carbon is -393.5 kJ/mol . What is the enthalpy change for the formation of 22 g of CO 2 from carbon and oxygen? -196.75 kJ -393.5 kJ -787.0 kJ -110.5 kJ The enthalpy of neutralization of HCl by NaOH is -57.1 kJ/eq . The heat evolved when 0.2 mole of HCl is mixed with 0.3 mole of NaOH is: 11.42 kJ 17.13 kJ 57.1 kJ 5.71 kJ Given the bond enthalpies of N N as 941 , kJ , mol -1 , H-H as 436 , kJ , mol -1 , and N-H as 391 , kJ , mol -1 , the enthalpy of formation of hydrazine ( N 2H 4 ) from its elements is ( N-N bond energy is 159 , kJ , mol -1 ): 98 , kJ , mol -1 -98 , kJ , mol -1 711 , kJ , mol -1 -711 , kJ , mol -1 If the enthalpy of combustion of diamond is -395.4 , kJ , mol -1 and that of graphite is -393.5 , kJ , mol -1 , the enthalpy change for the transition C(graphite) C(diamond) is: +1.9 , kJ , mol -1 -1.9 , kJ , mol -1 +788.9 , kJ , mol -1 -788.9 , kJ , mol -1 The enthalpy of solution of CaCl 2(s) is -82.9 , kJ , mol -1 and for CaCl 2 6H 2O(s) it is 19.1 , kJ , mol -1 . The enthalpy of hydration of CaCl 2 to CaCl 2 6H 2O is: -102.0 , kJ , mol -1 +102.0 , kJ , mol -1 -63.8 , kJ , mol -1 +63.8 , kJ , mol -1 For an ideal gas, the value of the parameter ( H / P) T is: 0 V V - T( V / T) P CP/R Given that the standard enthalpy of formation of O 3(g) is +142.7 , kJ , mol -1 , which of the following statements is true regarding the stability of ozone relative to oxygen? Ozone is less stable than oxygen because its formation is endothermic. Ozone is more stable than oxygen because its formation is endothermic. The conversion of ozone to oxygen is an endothermic process. Ozone and oxygen are equally stable because they are allotropes of the same element. The enthalpy of formation of CO 2(g) , H 2O(l) and CH 3OH(l) are -393.5 , -285.8 and -238.7 , kJ , mol -1 respectively. The enthalpy of combustion of CH 3OH(l) is: -726.6 , kJ , mol -1 -440.6 , kJ , mol -1 +726.6 , kJ , mol -1 -918.0 , kJ , mol -1 The bond enthalpy of C-H in ethane ( C 2H 6 ) is approximately 410 , kJ , mol -1 and the bond enthalpy of C-C is 348 , kJ , mol -1 . The enthalpy of atomization of ethane is: 2808 , kJ , mol -1 1578 , kJ , mol -1 2460 , kJ , mol -1 1982 , kJ , mol -1 The change in entropy for the fusion of 1 , mole of ice at 273 , K is 22.0 , J , K -1 , mol -1 . The molar enthalpy of fusion of ice is approximately: 6.0 , kJ , mol -1 12.0 , kJ , mol -1 22.0 , kJ , mol -1 2.2 , kJ , mol -1 Consider the following reaction: C(s) + 2H 2(g) CH 4(g) . H ⊖ = -74.8 , kJ . This value represents: Enthalpy of formation of methane Enthalpy of combustion of carbon Enthalpy of hydrogenation of carbon Enthalpy of atomization of methane Given the reactions: (i) H 2(g) + 1 2 O 2(g) H 2O(l), H = -286 , kJ ; (ii) H 2(g) + 1 2 O 2(g) H 2O(g), H = -242 , kJ . What is the enthalpy of vaporization of water? +44 , kJ , mol -1 -44 , kJ , mol -1 +528 , kJ , mol -1 -528 , kJ , mol -1 The absolute enthalpy of neutralisation of the reaction : MgO(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l) will be : - 57.33 kJ mol -1 -57.33 kJ mol -1 Greater than -57.33 kJ mol -1 Less than -57.33 kJ mol -1 Given that bond energies of H-H and Cl-Cl are 430 kJ mol -1 and 240 kJ mol -1 respectively and H f for HCl is – 90 kJ mol -1 , bond enthalpy of HCl is 380 kJ mol -1 425 kJ mol -1 245 kJ mol -1 290 kJ mol -1 From the following bond energies : H-H bond energy : 431.37 kJ mol -1 C=C bond energy : 606.10 kJ mol -1 C-C bond energy : 336.49 kJ mol -1 C-H bond energy : 410.50 kJ mol -1 Enthalpy for the reaction, will be : 553.0 kJ mol -1 1523.6 kJ mol -1 -243.6 kJ mol -1 -120.0 kJ mol -1 The bond dissociation energies of X2 , Y2 and XY are in the ratio of 1 : 0.5 : 1. H for the formation of XY is -200 kJ mol -1 . The bond dissociation energy of X2 will be 800 kJ mol -1 100 kJ mol -1 200 kJ mol -1 400 kJ mol -1 The standard heat of formation, in kcal/mol of Ba 2+ is : [Given : standard heat of formation of SO4 2- ion (aq) = -216 kcal/mol, standard heat of crystallisation of BaSO4(s) = -4.5 kcal/mol, standard heat of formation of BaSO4(s) = -349 kcal/mol] + 220.5 - 128.5 - 133.0 + 133.0 The standard enthalpy of formation of NH 3 is -46.0 , kJ , mol -1 . If the enthalpy for H 2 2H is 436 , kJ , mol -1 and that of N 2 2N is 941 , kJ , mol -1 , the bond enthalpy of N-H in NH 3 is: 391 , kJ , mol -1 -391 , kJ , mol -1 1173 , kJ , mol -1 230 , kJ , mol -1 The standard enthalpy of formation of C 2H 2(g) , CO 2(g) and H 2O(l) are 226.7 , -393.5 and -285.8 , kJ , mol -1 respectively. The standard enthalpy of combustion of C 2H 2(g) is: -1299.5 , kJ , mol -1 -1122.4 , kJ , mol -1 +1299.5 , kJ , mol -1 -1000 , kJ , mol -1 The enthalpy of hydrogenation of cyclohexene is -119.5 , kJ , mol -1 . If resonance energy of benzene is -150.4 , kJ , mol -1 , its enthalpy of hydrogenation would be: -208.1 , kJ , mol -1 -269.9 , kJ , mol -1 -358.5 , kJ , mol -1 -508.9 , kJ , mol -1 The bond enthalpy of H-H is 436 kJ mol -1 and Cl-Cl is 242 kJ mol -1 . If Δ f H of HCl is -91 kJ mol -1 , the bond enthalpy of H-Cl is: 430 kJ mol -1 245 kJ mol -1 339 kJ mol -1 769 kJ mol -1 Given that the standard enthalpies of formation of H 2O(l) and H 2O(g) are -285.8 , kJ , mol -1 and -241.8 , kJ , mol -1 respectively, the enthalpy of vaporization of water is: +44.0 , kJ , mol -1 -44.0 , kJ , mol -1 +527.6 , kJ , mol -1 -527.6 , kJ , mol -1 The heat of combustion of Yellow Phosphorus and Red Phosphorus are -9.91 kJ and -8.78 kJ respectively. The heat of transition of Yellow Phosphorus to Red Phosphorus is: -1.13 kJ +1.13 kJ +18.69 kJ -18.69 kJ The bond enthalpy of C-C bond is 348 , kJ , mol -1 and C=C is 612 , kJ , mol -1 . The enthalpy of hydrogenation of ethene ( C 2H 4 ) to ethane ( C 2H 6 ) is roughly (given bond enthalpy of H-H is 436 , kJ , mol -1 ): -124 , kJ , mol -1 124 , kJ , mol -1 -248 , kJ , mol -1 248 , kJ , mol -1 The enthalpy of atomization of CH 4 is 1665 , kJ/mol and that of C 2H 6 is 2826 , kJ/mol . What is the bond enthalpy of the C-C bond? 328.5 , kJ/mol 1161 , kJ/mol 416.25 , kJ/mol 832.5 , kJ/mol The enthalpy of formation of OH -(aq) is calculated using the enthalpy of neutralization of a strong acid and strong base ( -57.3 , kJ ) and the enthalpy of formation of H 2O(l) ( -285.8 , kJ ). The value is: -228.5 , kJ , mol -1 -343.1 , kJ , mol -1 228.5 , kJ , mol -1 343.1 , kJ , mol -1 If the bond enthalpies of H-H, Br-Br, and H-Br are 433, 192, and 364 kJ/mol respectively, the enthalpy of the reaction H 2(g) + Br 2(g) 2HBr(g) is: -103 kJ +103 kJ -261 kJ +261 kJ Given the following reactions: C + O 2 CO 2, H = -x kJ and 2CO + O 2 2CO 2, H = -y kJ . The enthalpy of formation of CO is: y/2 - x x - y/2 2x - y y - 2x The resonance energy of naphthalene is approximately -255 , kJ , mol -1 . If the heat of hydrogenation of a localized cyclohexene is -120 , kJ , mol -1 , the heat of hydrogenation of naphthalene to decalin ( C 10 H 18 ) is approximately: -345 , kJ , mol -1 -600 , kJ , mol -1 -855 , kJ , mol -1 -255 , kJ , mol -1 The standard enthalpy of formation of OH -(aq) is -228.5 , kJ , mol -1 . Given that the heat of neutralization of a strong acid and strong base is -57.3 , kJ , mol -1 , what is the enthalpy of formation of H 2O(l) ? (Assume f H[H +(aq)] = 0 ) -285.8 , kJ , mol -1 -171.2 , kJ , mol -1 -343.1 , kJ , mol -1 -228.5 , kJ , mol -1 Which of the following is true for the standard enthalpy of formation ( f H ) of elements in their standard states? It is taken as zero for all elements in their most stable form at 298 , K . It is always positive for gases. It is zero only for monoatomic gases like He . It depends on the method of synthesis. Which equation represents the standard enthalpy of formation of CH 4 ? C(graphite) + 2H 2(g) CH 4(g) C(diamond) + 2H 2(g) CH 4(g) C(g) + 4H(g) CH 4(g) CO(g) + 3H 2(g) CH 4(g) + H 2O(l) Which of the following processes is always exothermic? Combustion of a fuel Dissolution of a salt in water Vaporization of a liquid Decomposition of water