# MCQ on Chapter Thermochemistry ΔH, ΔE

1. For exothermic reactions, ΔH is _______ while for endothermic reactions it is _______.

(a) positive, negative

(b) positive, positive

(c) negative, negative

(d) negative, positive

2. The branch of chemistry which deals with the heat changes caused by chemical reactions is called _______

(a) thermodynamics

(b) thermal chemistry

(c) thermochemistry

(d) none of these

3. In an exothermic reaction, the internal energy of the products is _______ internal energy of the reactants.

(a) greater than

(b) lesser than

(c) equal to

(d) none of these

4. In an endothermic reaction _______

(a) ER > EP

(b) ER < EP

(c) ER = EP

(d) None of these

5. The enthalpy of a system is defined by the relation_______

(a) H = E + P V

(b) H = E – P V

(c) E = H + P V

(d) P V + E – H

6. In an exothermic reaction the heat energy is _______ while in endothermic reaction it is_______

(a) released, released

(b) released, absorbed

(c) absorbed, released

(d) absorbed, absorbed

7. Which one of the following is correct for a reaction aA + bB → cC + dD where Δn = (c + d) –(a + b)?

(a) PΔV = ΔH – ΔE

(b) ΔH = ΔE + Δn R T

(c) Δn R T = ΔH – ΔE

(d) all of these

8. For the reaction N2 + 3H2 ↽⇀ 2NH3, the change in enthalpy is given by_______

(a) ΔH = ΔE – 2 R T

(b) ΔH = ΔE + 2 R T

(c) ΔH = ΔE + 3 R T

(d) ΔH = ΔE + R T

9. ΔH = ΔE is true for the reaction_______

(a) H2 + Cl2 ↽⇀ 2HCl

(b) 2NO ↽⇀ N2 + O2

(c) 2HI ↽⇀ H2 + I2

(d) all of these

10. Which of the following relations holds good for the reaction: CO(g) + ½O2(g) → CO2(g) ?

(a) ΔH = ΔE

(b) ΔH = ΔE + R T

(c) ΔH = ΔE + ½ R T

(d) Δ H = Δ E – ½ R T

11. The change in internal energy with temperature at a constant volume is given by the relation _______

(a) ΔE = ΔCv (T1 – T2)

(b) ΔE = ΔCp (T2 – T1)

(c) ΔE = ΔCv (T2 – T1)

(d) ΔE = ΔCp (T1 – T2)

12. The Kirchoff’s equation is _______

(a) ΔH2 – ΔH1 = ΔCp (T2 – T1)

(b) ΔE– ΔE1 = ΔC(T2 – T1)

(c) both

(d) neither (a) nor (b)

13. The change in enthalpy that takes place when one mole of the compound is formed from its elements is called _______

(a) heat of formation of compound

(b) heat of synthesis

(c) heat of combustion

(d) standard heat of formation

14. By convention, the standard heat of formation of all elements is assumed to be _______

(a) zero

(b) negative

(c) positive

(d) infinity

15. The change in enthalpy of a system when one mole of the substance is completely burnt in excess of air or oxygen is called _______

(a) heat of reaction

(b) heat of formation

(c) heat of oxidation

(d) heat of combustion

16. The calorific value is defined as the amount of heat produced in calories when _______ of a substance is completely burnt.

(a) one gram (b) one mole

(c) 100 grams (d) 1 kg

17. The fuel efficiency of methane (mol mass = 16) is _______ that of ethane (mol mass = 30).

(a) lesser than

(b) greater than

(c) equal to

(d) none of these

18. Which of the following always has a negative value?

(a) heat of formation

(b) heat of reaction

(c) heat of combustion

(d) heat of solution

19. The change in enthalpy when one mole of a substance is dissolved in a specified quantity of solvent at a given temperature is called _______

(a) heat of reaction

(b) heat of combustion

(c) heat of solvation

(d) heat of solution

20. The change in enthalpy of the system when one ________ of an acid is neutralised by one _______ of a base or vice versa in dilute solution is called heat of neutralisation.

(a) g-equivalent, mole

(b) mole, g-equivalent

(c) g-equivalent, g-equivalent

(d) mole, mole

21. The heat of neutralization of a strong acid and a strong base is always _______

(a) zero

(b) constant

(c) positive

(d) changing

22. The heat of neutralization is of a weak acid by a strong base is _______ that of a strong acid by a strong base.

(a) lesser than

(b) greater than

(c) equal to

(d) none of these

23. The heat change in equations H+(aq) + OH(aq) → H2O( ℓ ) ΔH = –13.7 kcal represents_______

(a) heat of neutralization

(b) heat of formation of water

(c) heat of dissociation of water

(d) heat of solution

24. The heat change (or enthalpy change) when one mole of a solid substance is converted into the liquid state at its _______ is called heat of fusion.

(a) boiling point

(b) melting point

(c) freezing point

(d) evaporation point

25. The process depicted by the equation H2O(s) → H2O( ℓ) ΔH = + 1.43 kcal represents_______

(a) melting

(b) boiling

(c) evaporation

(d) fusion

26. Greater the heat of fusion of a substance ______ is the magnitude of intermolecular forces.

(a) higher

(b) lower

(c) zero

(d) infinite

27. The heat change when one mole of a liquid is converted into vapour or gaseous state at its boiling point is called _______

(a) heat of liquefaction

(b) heat of fusion

(c) heat of vaporization

(d) heat of sublimation

28. The process of sublimation for a solid occurs _______

(a) at the melting point

(b) at a temperature below its melting point

(c) at a temperature above its melting point

(d) none of these

29. The change in enthalpy which occurs when one mole of an element changes from one allotropic form to another is called _______

(a) heat of allotropy

(b) heat of transition

(c) heat of transformation

(d) heat of sublimation

30. The thermochemical equations may be_______

(a) multiplied

(c) subtracted

(d) all of these

31. In a chemical process, the amount of total heat change is same no matter by which method the change is brought about. This is statement of_______

(a) law of thermochemistry

(b) Hess’s law

(c) thermodynamic law

(d) law of heat of reaction

32. The average amount of energy required to break all bonds of a particular type in one mole of the substance is called_______

(a) heat of reaction

(b) bond energy

(c) heat of transition

(d) heat of bond formation

33. The bond energy depends upon_______

(a) size of the atom

(b) electronegativity

(c) bond length

(d) all of these

34. When a bond is broken, the bond energy is positive because heat _______

(a) is evolved

(b) is absorbed

(c) remains unchanged

(d) none of these

35. For an endothermic reaction_______

(a) ΔH is –ve

(b) ΔH is +ve

(c) ΔE is –ve

(d) ΔH is zero

36. The enthalpy change in the reaction 2CO + O2 → 2CO2 is termed as _______

(a) enthalpy of reaction

(b) enthalpy of fusion

(c) enthalpy of formation

(d) enthalpy of combustion

37. For a reaction A2(g) + B2(g) → 2AB(g)  ΔH = x kcal According to this reaction, the heat of formation of AB will be _______

(a) x kcal

(b) –x kcal

(c) x/2 kcal

(d) –x/2 kcal

38. For a gaseous reaction X(g) + Y(g) → 4Z(g)   ΔE at 300 K is 20 kcal. Taking R = 2 cal K–1 mol–1, ΔH for the above reaction will be_______

(a) 18.8 kcal

(b) 19.4 kcal

(c) 20.0 kcal

(d) 21.2 kcal

39. The heat of neutralization of an acid A with a base B is 13.7 kcal. Which of the following is true _______

(a) A is weak and B is also weak

(b) A is strong and B is weak

(c) A is weak and B is strong

(d) A is strong and B is also strong

40. For which of the following reactions, will ΔH be equal to ΔE?

(a) N2(g) + 3H2(g) → 2NH3

(b) 2HI(g) → H2(g) + I2(g)

(c) 2NO2 → N2O4(g)

(d) 2SO2(g) + O2(g) → 2SO3(g)

41. The neutralization of an acid with a base is represented by H+(aq) + OH(aq) → H2O (ℓ )  ΔH = –13.7 kcal The heat of neutralization of one mole of H2SO4 with sodium hydroxide will be _______

(a) –13.7 kcal

(b) –27.4 kcal

(c) +27.4 kcal

(d) –6.85 kcal

42. Given that heat neutralization of strong acid and strong base is –13.7 kcal. The heat produced when one mole of HCl is mixed with 0.5 mole of NaOH will be _______

(a) 6.85 kcal

(b) – 6.85 kcal

(c) –27.4 kcal

(d) –13.7 kcal

43. The apparatus used to measure heat changes during chemical reactions is called_______

(a) polarimeter

(b) colorimeter

(c) calorimeter

(d) none of these

44. Hess’s law is used to determine _______

(a) heat of formation of substances which are otherwise difficult to measure

(b) heat of transition

(c) heats of various other reactions like dimerization

(d) all of the above

45. ΔH° represent the enthalpy change _______

(a) at 0°C and 1 atm pressure

(b) at 0 K and 1 atm pressure

(c) at 25 K and 1 atm pressure

(d) none of these

46. The heats of formation of CO(g) and CO2(g) are –26.4 kcal and –94.0 kcal respectively. The heat of combustion of carbon monoxide according to Hess’s law will be _______

(a) +26.4 kcal

(b) + 94.0 kcal

(c) – 67.6 kcal

(d) –120.4 kcal

47. The heat of combustion of ethane (C2H6) is –337.0 kcal at 25°C. The heat of the reaction when 3 g of ethane is burnt completely is_______

(a) –3.37 kcal

(b) +3.37 kcal

(c) –33.7 kcal

(d) +33.7 kcal

48. For the reaction CaCO3(s) → CaO(s) + CO2(g) which one of the following is true?

(a) ΔH = ΔE

(b) ΔH > ΔE

(c) ΔH < ΔE

(d) ΔH = ½ ΔE

49. Consider the reaction: CO(g) + ½O2(g) → CO2(g) at constant temperature and pressure. Which one of the following is correct?

(a) ΔH < ΔE

(b) ΔH > ΔE

(c) ΔH = ΔE

(d) none of these

50. The energy required to dissociate 6 g of gaseous hydrogen into free gaseous atoms is 3.12 kcal at 25°C. The bond energy of H–H bond will be _______

(a) 3.12 kcal

(b) 1.56 kcal

(c) 1.04 kcal

(d) 10.04 kcal