Free NEET Chemistry multiple-choice questions on Enthalpy & Heat Capacity. Attempt each question and reveal the answer with a full explanation.
Which of the following is an intensive property? Molar heat capacity Internal energy Enthalpy Volume The heat capacity of a monoatomic ideal gas at constant pressure ( C p ) is 20.8 , J , K -1 , mol -1 . What is its C v ? 12.5 , J , K -1 , mol -1 29.1 , J , K -1 , mol -1 8.3 , J , K -1 , mol -1 20.8 , J , K -1 , mol -1 Which of the following is NOT an intensive property? Heat capacity Temperature Density Pressure Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? H = U - n g RT H = U + n g RT H - U = - nRT H + U = nR For the reaction C 3H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2O(l) at constant temperature, H - U is: -3RT -RT +3RT -2RT For which of the following reactions is H equal to U ? H 2(g) + I 2(g) 2HI(g) N 2(g) + 3H 2(g) 2NH 3(g) 2SO 2(g) + O 2(g) 2SO 3(g) C(s) + O 2(g) CO 2(g) The molar heat capacity of water at constant pressure is 75 , J , K -1 , mol -1 . When 1.0 , kJ of heat is supplied to 100 , g of water, the increase in temperature is: 2.4 , K 1.2 , K 4.4 , K 6.6 , K In a reaction where n g = -2 , if the temperature is increased at constant pressure, how does H - U change? Increases in magnitude (more negative) Decreases in magnitude Remains constant Becomes zero The variation of enthalpy of a reaction with temperature is given by which of the following equations? Kirchhoff's equation Clausius-Clapeyron equation Gibbs-Helmholtz equation Van't Hoff equation For an ideal gas, the relationship between C p and C v is C p - C v = R . This R represents: Work done by one mole of gas in expansion when temperature is raised by 1 K Heat absorbed by the gas The internal energy of the gas The entropy change of the gas The internal energy change ( ΔU ) for the reaction CH 4(g) + 2O 2(g) ightarrow CO 2(g) + 2H 2O(l) at 298 K is related to ΔH by: ΔH = ΔU - 2RT ΔH = ΔU + 2RT ΔH = ΔU - RT ΔH = ΔU + RT For the decomposition of calcium carbonate, CaCO 3(s) CaO(s) + CO 2(g) , the relationship between the enthalpy change ( H ) and the internal energy change ( U ) is given by: H = U + RT H = U - RT H = U + 2RT H = U For the reaction N 2(g) + 3H 2(g) 2NH 3(g) , what is the relationship between H and U at temperature T ? H = U - 2RT H = U + 2RT H = U - RT H = U + RT For the reaction CO(g) + 1 2 O 2(g) CO 2(g) , the value of H - U at 300 , K is: ( R = 8.314 , J , K -1 , mol -1 ) -1247.1 , J 1247.1 , J -2494.2 , J 2494.2 , J Which of the following equations correctly represents Kirchhoff's equation? H 2 - H 1 = C p(T 2 - T 1) U 2 - U 1 = C p(T 2 - T 1) H 2 - H 1 = C v(T 2 - T 1) G 2 - G 1 = S(T 2 - T 1) For a linear triatomic gas like CO 2 , the ratio of molar heat capacity at constant pressure to that at constant volume ( = C p/C v ), assuming vibrational modes are not active, is: 1.40 1.66 1.33 1.25 For a mixture of 1 , mol of a monoatomic gas and 1 , mol of a diatomic gas, the value of = C p/C v is: 1.50 1.40 1.66 1.33 For the reaction N 2(g) + 3H 2(g) 2NH 3(g) , the variation of enthalpy change with temperature is given by d( H) dT = C p . If C p is negative, then: H decreases with increase in temperature H increases with increase in temperature H remains constant H first increases then decreases The molar heat capacity of an ideal gas at constant pressure ( C p ) for a non-rigid diatomic molecule, including vibrational degrees of freedom, is: 9 2 R 7 2 R 5 2 R 4R For the reaction N 2(g) + 3H 2(g) 2NH 3(g) , the enthalpy change H and internal energy change U are related by: H = U - 2RT H = U + 2RT H = U - RT H = U + RT The molar heat capacity of an ideal gas at constant pressure ( C p ) is 3.5R . The ratio of specific heats ( = C p/C v ) for this gas is: 1.40 1.66 1.33 1.25 The difference between C p and C v is practically negligible for: Solids and liquids Ideal gases Real gases Diatomic gases Which of the following properties is an extensive property but its corresponding molar value is an intensive property? Heat capacity Temperature Pressure Density The molar heat capacity of a mixture containing 2 , moles of He and 3 , moles of H 2 at constant volume ( C v ) is: 2.1R 1.5R 2.5R 1.9R Which of the following statements correctly describes Kirchhoff's law? It describes the variation of the enthalpy of a reaction with temperature. It states that the total enthalpy change of a reaction is independent of the path taken. It relates the equilibrium constant to the standard free energy change. It states that entropy increases for all spontaneous processes. The molar heat capacity of an ideal monoatomic gas at constant volume is C v = 1.5R . For a non-rigid diatomic gas molecule at high temperatures, the value of C v is: 3.5R 2.5R 1.5R 4.5R Consider the following liquid - vapour equilibrium. Liquid Vapour Which of the following relations is correct ? d G dT 2 = H v RT 2 d P dT =- H v RT d P dT 2 =- H v T 2 d P dT = H v RT 2 Standard enthalpy of vaporisation vap H for water at 100 C is 40.66 , kJ , mol -1 . The internal energy change for vaporisation of water at 100 C (in kJ , mol -1 ) is: +37.56 -43.76 +43.76 +40.66 The enthalpy of neutralization of HF by NaOH is -68.6 , kJ , mol -1 , which is higher than the standard value for strong acids ( -57.1 , kJ , mol -1 ). This is because: The hydration energy of F - ion is very high. HF is a very strong acid. The bond dissociation energy of HF is very low. Fluorine is the most electronegative element. The molar heat capacity of an ideal gas at constant pressure is C p . If the gas undergoes a reversible adiabatic expansion from (P 1, V 1, T 1) to (P 2, V 2, T 2) , the work done is given by: n(C p - R)(T 1 - T 2) nC p(T 2 - T 1) nRT (V 2/V 1) P 2 V 2 - P 1 V 1 For a polytropic process PV n = constant , the molar heat capacity C of an ideal gas is given by: C = C v + R 1-n C = C v - R 1-n C = C p + R 1-n C = C v + nR During the combustion of 1 , mole of liquid benzene ( C 6H 6 ) in a bomb calorimeter, U was found to be -3263.9 , kJ , mol -1 at 25 C . The enthalpy of combustion H for the reaction C 6H 6(l) + 7.5O 2(g) 6CO 2(g) + 3H 2O(l) is: -3267.6 , kJ , mol -1 -3260.2 , kJ , mol -1 -3263.9 , kJ , mol -1 -3271.3 , kJ , mol -1 The molar heat capacity of an ideal gas at constant pressure is 20.8 , J , K -1 , mol -1 . The molar heat capacity at constant volume will be: ( R = 8.314 , J , K -1 , mol -1 ) 12.486 , J , K -1 , mol -1 29.114 , J , K -1 , mol -1 20.8 , J , K -1 , mol -1 8.314 , J , K -1 , mol -1 The heat capacity of a solid is C . If the mass of the solid is doubled, the heat capacity becomes: 2C C/2 C 4C The molar heat capacity of a diatomic gas like O 2 at constant volume ( C v ) at moderate temperatures is: 5 2 R 3 2 R 7 2 R R The molar heat capacity of an ideal monoatomic gas at constant volume ( C v ) is: 3 2 R 5 2 R 3R R For the decomposition of ammonium chloride: NH 4Cl(s) NH 3(g) + HCl(g) , the relationship between H and U is: H = U + 2RT H = U + RT H = U - 2RT H = U A non-linear triatomic molecule like H 2O (ignoring vibrational modes) has a molar heat capacity at constant volume ( C v ) equal to: 3R 1.5R 2.5R 3.5R