ENTHALPY CHANGE & HESS's LAW ( WS #4 ) Q1. H and E for the reaction, S(s) + 3 O(g) SO3(g) are related as: (a) H = E 0.5 RT (b) H = E 1.5RT (c) H = E + RT (d) H = E + 1.5 RT Q. The enthalpy of solution of BaCl (s) and BaCl.H O(s) are 0.6 and 8.8 kj mol -1 respectively. The enthalpy change for the reaction,bacl (s) + H O Bacl.H O(s); is: (a) 9.4 kj (b) 11.8 kj (c) 0.6 kj (d) 9.4 kj Q3. The heat of combustion of CH 4(g), C(graphite) and H (g) are 0 kcal, - 40 kcal and 10 kcal respectively. The heat of formation of methane is: (a) 40 kcal (b) + 40 kcal (c) 80 kcal (d) + 80 kcal Q4. Under identical conditions, how many ml of each 1 M KOH and 0.5 M H SO 4 solutions are required to produce a resulting volume of 100 ml with the highest rise in temperature? (a) 75, 5 (b) 5, 75 (c) 60, 40 (d) 50, 50 Q5. A solution of 500 ml of 0. M KOH and 500 ml of 0. M HCl is mixed and stirred, the rise in temperature is T i. The experiment is repeated using 50 ml each of solution, the temperature raised is T. Which of the following is true? (a) T 1 = T (b) T 1 = T (c) T 1 = 4T (d) T = 9T 1 Q6. Identify the reaction in which the heat liberated corresponds to the heat of formation ( H): (a) C (diamond) + O (g) CO (g) + heat (b) H (g) + O (g) H O(g) + heat (c) C (diamond) + H (g) CH 4(g) + heat (d) S (rhombic) + O (g) SO (g) + heat Q7. Which of the following is an endothermic reaction? (a) H (g) + O (g) H O(l) (b) N (g) + O (g) NO(g) (c) NaOH(aq) + HCl(aq) NaCl(aq) + H O(l) (d) C H 5OH(aq) + 3O (g) CO (g) + 3H O(l) Q8. Which of the following reactions is exothermic? (a) CH 4(g) + O (g) CO (g) + H O(l) (b) Fe(s) + S(s) FeS(s) (c) NaOH(aq) + HCl(aq) NaCl(aq) + H O(l) (d) All of these Q9. Which one of the following is not applicable for a thermochemical equation? (a) It tells about physical state of reactants and products (b) It tells whether the reaction is spontaneous (c) It tells whether the reaction is exothermic or endothermic (d) It tells about the allotropic form (if any) of the reactants Q10. The enthalpies of all elements in their standard state at 5 C and one atmosphere pressure are: (a) same (b) always positive (c) always negative (d) zero Q11. According to the equation,c 6H 6(l) + 15 O(g) 6CO(g) + 3HO(l); H = -364.4 kj mol-1 the energy evolved when 7.8 g benzene is burnt in air will be: (a) 163. kj (b) 3.64 kj (c) 3.64 kj (d) 36.4 kj SCO#03, SECOND FLOOR, SECTOR -14, PANCHKULA ; 987844971, 988801971, 9417655033 Page 1
Q1. The enthalpy change for the reaction,c (graphite) + 3H (g) C H 6(g)is called: (a) enthalpy of formation (b) enthalpy of combustion (c) enthalpy of hydrogenation (d) enthalpy of vaporization Q13. The heat of combustion of C (graphite) is -393.5 kj mol -1. The heat of formation of CO from graphite is.. kj mol -1 : (a) 393.5 (b) -393.5 (c) -787.0 (d) 787.0 Q14. The heat of neutralization of any strong acid and strong base is always constant and H = - 57.3 kj. This is because: (a) both the acid and base undergo complete ionization (b) during neutralization, salt and water are formed (c) 1 mole of water is formed from H + and OH - ions (d) the reaction is exothermic Q15. The amount of heat liberated when one mole of NH 4OH reacts with one mole of HCl is: (a) 13.7 kcal (b) more than 13.7 kcal (c) less than 13.67 kcal (d) cannot be predicted Q16. Heat of neutralization for the reaction,naoh + HCl NaCl + H O is 57.1 kj mol -1. The heat released when 0.5 mole of NaOH is titrated against 0.5 mole of HCl will be ; (a).5 kj (b) 57.1 kj (c) 8.6 kj (d) 14.3 kj Q17. In which of the following neutralization reactions, the heat of neutralization will be highest? (a) HCl and NaOH (b) CH 3COOH and NaOH (c) CH 3COOH and NH 4OH (d) HCl and NH 4OH Q18. The enthalpy of formation of a compound is equal in magnitude but of opposite sign to the enthalpy of decomposition of that compound under the same conditions. This law was presented by: (a) Hess (b) Le Chatelier (c) Kirchhoff (d) Lavoisier and Laplace Q19. The change of enthalpy of a chemical reaction is the same whether the reaction takes place in one step or in several steps. This law was presented by: (a) Hess (b) Le Chatelier (c) van t Hoff (d) Kirchhoff Q0. 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: (a) -18.69 kj (b) +1.13 kj (c) +18.69 kj (d) -1.13 kj Q1. What will be the heat of formation of methane, if the heat of combustion of carbon is -x kj, heat of formation of water is -y kj and heat of combustion of methane is -z kj? (a) (-x y + z) kj (b) (-z x + y) kj (c) (-x y z) kj (d) (-x y + z) kj Q. Given, C(s) + O (g) CO (g) + 94. kcal H (g) + ½ O (g) H O(l) + 68.3 kcal CH 4(g) + O (g) CO (g) + H O(l) + 10.8 kcal. H form ( CH4) is : (a) 45.9 (b) 47.8 (c) 0.0 (d) 47.3 Q3. On combustion carbon forms two oxides CO and CO, heat of formation of CO is -94.3 kcal and that of CO is -6.0 kcal. Heat of combustion of carbon is: (a) -6.0 kcal (b) -68.3 kcal (c) -94.3 kcal (d) -10.3 kcal SCO#03, SECOND FLOOR, SECTOR -14, PANCHKULA ; 987844971, 988801971, 9417655033 Page
Q4. Standard heat of formation for CCl 4, H O, CO and HCl at 98 K are -5.5, -57.8, -94.1 and -.1 kj/mol respectively. For the reaction,ccl 4 + H O CO + 4HCl, what is H? (a) 36.4 kj (b) 0.7 kj (c) -0.7 kj (d) -41.4 kj Q5. Heat of combustion of CH 4, C H 6, C H 4 and C H are -1.8, -373.0, -337.0 and -310.5 kcal respectively at the same temperature. The best fuel among these gases is: (a) CH 4 (b) C H 6 (c) C H 4 (d) C H Q6. If enthalpies of formation for C H 4(g), CO (g) and H O(l) at 5 C and 1 atm pressure be 5, -394 and -86 kj mol -1 respectively, enthalpy of combustion of C H 4(g) will be: (a) +141. kj mol -1 (b) +141 kj mol -1 (c) -141. kj mol -1 (d) -141 kj mol -1 Q7. S + 3 O SO3 + x kcal;so + ½ O SO3 + y kcal. The heat of formation of SO is: (a) y x (b) x + y (c) x + y (d) x/y Q8. The heat of formation ( H o f ) of H O(l) is equal to: (a) zero (b) molar heat of combustion of H (l) (c) molar heat of combustion of H (g) (d) sum of heat of formation of H O(g) and O (g) Q9. The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at 5 C increases the temperature of 18.94 kg of water by 0.63 C. If the specific heat of water at 5 C is 0.998 cal g -1 deg -1, the value of heat of combustion of benzoic acid is: (a) 881.1 kcal (b) 771.4 kcal (c) 981.1 kcal (d) 871. kcal Q30. In an insulated container mole of a liquid, molar volume 100 ml at 1 bar. Liquid is steeply taken to 100 bar, when volume of liquid decreases by 1 ml. Find H and U for the process.ans : E = 100 bar ml, H = 9900 bar ml Q31. The reaction, NH CN(s) + 3 O(g) N(g) + CO(g) + HO(l); is carried out in a bomb calorimeter and the heat liberated during the course of reaction was found to be -74.7 kj mol -1 at 5 o C. Calculate the heat of reaction at constant pressure at 5 o C. 741.4 kj Q3. When 1.0 g of carbon reacted with oxygen to form CO and CO at 5 o C and constant pressure, 75.0 kcal of heat was liberated and no carbon remained. Calculate the mass of oxygen needed for it and the mole of CO and CO formed. Given, H f CO = -94.05 and H f CO = -6.41 kcal mol -1. mole of CO, CO are 0.7 &0.8, mass of O = 7.5 g Q33. Calculate the lattice enthalpy of LiF; given that the enthalpy of (i) Sublimation of lithium is 155. kj/mole. (ii) Dissociation of 1 mole of F at 75.3 kj/mole. (iii) Ionisation of lithium is 50 kj/mole. (iv) Electron gain enthalpy of 1 mole of F(g) is -333 kj. (v) H f overall is -594.1 kj/mole. Ans : 973.8 kj/mole Q34. Calculate the lattice enthalpy of MgBr given that Enthalpy of formation of MgBr = - 54 kj mol -1 Sublimation energy of Mg = 148 kj mol -1 Ionization energy of Mg = 187 kj mol -1 SCO#03, SECOND FLOOR, SECTOR -14, PANCHKULA ; 987844971, 988801971, 9417655033 Page 3
Vaporisation energy of Br (l) = 31 kj mol -1 Dissociation energy of Br (g) = 193 kj mol -1 Electron gain enthalpy of Br(g) = 331 kj mol -1 Ans : 640 kj/mole Q35. Calculate the enthalpy of vaporization for water from the following: H (g) + 1 O(g) HO(g); H = -57.0 kcal H (g) + 1 O(g) HO(l); H = -68.3 kcal Also calculate the heat required to change 1 g H O(l) to H O(g). Q36. Calculate the heat of transition for carbon from the following: + 11.3 kcal. C diamond + O CO (g); H = -94.3 kcal C Amorphous + O CO (g); H = -97.6 kcal Also calculate the heat required to change 1 g of C Diamond to C Amorphous. 0.75kcal/g Q37. An intimate mixture of Fe O 3 and Al is used in solid fuel rocket. Calculate the fuel value per g and per ml of mixture. H = 399.0 kcal, H Al O 3 FeO = 199.0 kcal, density of FeO3 and Al are 5. g/ml and 3.7 g/ml respectively. Ans : 0.934 Kcal/g, 3.94 Kcal/ml Q38. The heat of solution of anhydrous CuSO 4 is -15.9 kcal and that of CuSO 4, 5H O is.8 kcal. Calculate the heat of hydration of CuSO 4. Q39. What would be heat released when: Ans : 18.7 Kcal (i) 0.5 mole of HCl in solution is neutralized by 0.5 mole of NaOH solution? (ii) 0.5 mole of HNO 3 in solution is mixed with 0. mole of KOH solution? (iii) 00 cm 3 of 0. M HCl is mixed with 300 cm 3 of 0.1 M NaOH solution? (iv) 400 cm 3 of 0. M H SO 4 is mixed with 300 cm 3 of 0.1 M NaOH solution? Ans : (i) 14.7 kj (ii) 11.4 kj (iii) 1.713 kj (iv) 1.713 kj Q40. When 0.05 mole of HCl(aq) reacts with 0.05 mole of NaOH(aq) to form 0.05 mole of NaCl(aq),.9 kj of heat is produced. What is ΔH, the enthalpy change per mole of acid reacting for the acid-base reaction under standard state? 58 kj/mole Q41. Calculate the heat of neutralization from the following data. 00 ml. of 1 M HCl is mixed with 400 ml. of 0.5 M NaOH. The temperature rise in calorimeter was found to be 4.4 C. Water equivalent of calorimeter is 1 g and specific heat is 1 cal/ml/degree, for solution Q4. The heat of combustion of ethyl alcohol (C H 5OH) is 1380.7 kj mol -1. If the heat of formation of CO and H O are 394.5 and 86.6 kj mol -1 respectively, calculate the heat of formation of ethyl alcohol. Q43. Heat of solution (ΔH soln) for BaCl.H O and BaCl are 8.8 and 0.6 kj mol -1 respectively. Calculate the heat of hydration of BaCl to BaCl.H O. 9.4 kj/mole Q44. Calculate the heat change accompanying the transformation of C (graphite) to C (diamond), given that the heats of combustion of graphite and diamond are 393.5 and 395.4 kj mol -1 respectively. + 1.9 kj1 SCO#03, SECOND FLOOR, SECTOR -14, PANCHKULA ; 987844971, 988801971, 9417655033 Page 4
SCO#03, SECOND FLOOR, SECTOR -14, PANCHKULA ; 987844971, 988801971, 9417655033 Page 5