DAV PUBLIC SCHOOL HEHAL
RANCHI 834005
Worksheet Name: Thermochemistry Standard: 11th Science Subject: Chemistry
Instructions
1. SOLVE ALL QUESTION
Q1. Define the term entropy. Write its unit. How does entropy of a system change on increasing temperature?
Q2. Hess's law is related to:
A Change in heat during a reaction B Rates of reaction
C Equilibrium constant D Influence of pressure on volume of a gas
Q3.
DAV PS HEHAL DEPT. OF
CHEMISTRY.
Name the type of wall used in the above figure.
A Adiabatic walls. B Thermally insulating walls.
C Thermally conducting walls. D None of the above.
Q4. In the equation, N 2 (g) + 3H2 (g) ⇌ 2NH3 (g) would be the sign of work done?
Q5. Why does NH4NO3 dissolve in water spontaneously even when this process is endothermic?
Q6. Which of the following is technique used to measure the heat of a reaction?
A Gibbs Free Energy B Entropy C Enthalpy D Calorimetry
Q7. Two moles of an ideal gas is expanded isothermally and reversibly from 1L to 10L at 300K. The enthalpy change (in kJ) for the process is:
A 11.4kJ B -11.4kJ C 0kJ D 4.8kJ
Q8. When an ideal gas expands into vacuum, there is neither absorption nor evolution of heat. Why?
Q9. Hess's law is used to calculate:
A Enthalpy of reaction B Entropy of reaction C Work done in reaction D All the above
Q10. What is the change in the energy of system if 500cal of heat energy are added to a system and system does 350cal of work on the
surroundings?
A -150cal B +150cal C +850cal D -850cal
Q11. The internal energy U is a unique function of any state because change in U:
A Does not depends upon path B Depends upon path
C Corresponds to adiabatic process D Corresponds to an isothermal process
Q12. What is the value of ΔG when ice and water are in equilibrium?
Q13. Under what condition, the heat evolved or absorbed in a reaction is equal to its free energy change?
Q14. Identify the state functions and path functions out of the following : enthalpy, entropy, heat, temperature, work, free energy.
Q15. A thermochemical equation:
A Includes only the balanced chemical reaction B Includes the balanced chemical reaction and change in
enthalpy value
C Includes only the change in enthalpy value D None of these options
E Includes the unbalanced chemical reaction and change in
enthalpy value
Q16. Which of the following are state functions?
A Enthalpy. B Heat. C Free energy. D Work.
Q17. Which of the following is an extensive property?
A Temperature. B Density. C Gibbs free energy. D Molar volume.
Q18. In which of the processes, does the internal energy of the system remain constant?
A Adiabatic B Isochoric C Isobaric D Isothermal
Q19. Vf
The pressure-volume work for an ideal gas can be calculated by using the expression w = − ∫ p
ex
dV . The work can also be calculated from
Vt
the PV– plot by using the area under the curve within the specified limits. When an ideal gas is compressed (a) reversibly or (b) irreversibly
from volume Vi to Vf . choose the correct option.
A w (reversible) = w (irreversible). B w (reversible) < w (irreversible).
C w (reversible) > w (irreversible). D w(reversible) = w (irreversible) +p ex
. ΔV.
Q20. In the given reaction, Na(s) → Na(g)
The enthalpy of atomisation is same as the:
A Enthalpy of dissociation. B Enthalpy of sublimation.
C Enthalpy of association. D Enthalpy of vaporisation.
Q21. Name the state variables which remain constant in:
1. Isobaric process.
2. Isothermal process.
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Q22. For a spontaneous process:
CHEMISTRY.
A enthalpy change of the system must be negative B entropy change of the system must be positive
C entropy change of the surrounding must be positive D entropy change of the system plus surrounding must be
positive
Q23. Internal energy per mole of gas depends on
A Viscosity B Density C Temperature D Thermal conductivity
Q24. The heat released when the requisite amount of ions in the gaseous state combine to give 1 mol of crystal lattice is known as:
A lattice energy B hydration energy C formation energy D none of the above
Q25. Which of the following processes is a nonspontaneous process?
A Dissolution of salt or sugar in water B Mixing of different gases through diffusion
C Precipitation of copper when zinc rod is dipped in aqueous D Flow of heat from a cold body to a hot body in contact of
solution of copper sulphate these
Q26. For a reaction to be spontaneous, the sign on delta G should be :
A positive B There should be no sign
C Negative D Spontaneity is not related to Gibbs Free Energy
E Positive or Negative
Q27. Lattice enthalpies are determined by:
A Born-Haber cycle. B Hess' law. C Lattice cycle. D None of these.
Q28. Which of the following is not true about a reversible reaction?
A The reaction does not proceed to completion B It cannot be influenced by a catalyst
C Number of moles of reactants and products is always equal D It can be attained only in a closed container
Q29. Regarding a thermochemical equation, wrong statement is:
A It tells about the physical states of reactants and products B It tells whether the reaction is exothermic or endothermic
C It tells about the allotropic form (if any) of the reactant D It tells whether the reaction is possible or not
Q30. Calculate the standard enthalpy of formation of CH3OH(l) from the following data:
3 ⊖ −1
CH3 OH(I) + O2 (g) −
−→ CO2 (g) + 2H2 O(I); Δr H = −726kJ mol
2
⊖ −1
C(graphite) + O2(g) −
−→ CO2(g) ; Δc H = −393kJ mol
H2 (g) +
1
2
O2(g) −
−→ H2 O(I); Δf H
⊖
= −286kJ mol
−1
.
Q31. Calculate the enthalpy change for the process
CCI4 (g) −→ C(g) + 4CI(g)
and calculate bond enthalpy of C – Cl in CCl4(g).
⊖ −1
Δvap H (CCI4 ) = 30.5kJ mol .
⊖ −1
Δf H (CCI4 ) = −135.5kJ mol .
Δa H
⊖
(C) = −715.0kJ mol
−1
, where Δ aH
⊖
is enthalpy of atomisation
⊖ −1
Δa H (CI2 ) = 242kJ mol
Q32. 1. Heat(q) and work done (W) individually are not state functions but their sum is always a state function. Explain why?
2. Calculate the standard enthalpy change (Δ H ) and standard internal energy change (Δ U ) for the following reaction at 300K:
r
θ
r
θ
OF2(g) + H2O(g) + O2(g) + 2HF(g)
Standard enthalpy of formation (Δ H ) of e n various species are given below:
r
θ
-1 -1
: OF2(g) = 23.0, H2O(g)= -241.8, HF(g) = -268.6, R = 8.314 JK mol .
θ −1
Δ H kJ mol
f
Q33. 1. Derive the mathematical expression for first law of thermodynamics.
2. Calculate the Δ H for the reaction:
r
∘
H2(g) + Br2(g) → 2HBr(g)
Bond enthalpy are given as, H-H = 436kJ mol-1, Br-Br = 192kJ mol-1 and H-Br = 368kJ mol-1
Q34. The figure given below represents pV diagram of different stages of a thermodynamic process. Calculate the work done in each stage and
also the net work done in the complete cyclic process.
DAV PS HEHAL DEPT. OF
CHEMISTRY.
Q35. 1. Define standard enthalpy of formation. Explain why the enthalpy changes for the reaction given below are not enthalpies of formation
of CaCO3 and HBr:
−−
−→
1. CaO(s) + CO (g)
∘ −1
2 CaCO (s); Δ H = −178.3kJ mol 3 r
−−→
2. H
(g) + Br (g)
2 22HBr(g); Δ H = −72.8kJ mol r
∘ −1
2. Use the bond enthalpies listed below to determine the enthalpy of reaction:
H
−→
H − C − H(g) + 2O = O(g) O = C = O(g)
+ 2H − O − H(g)
Bond enthalpy (ΔH ∘
)/kJ mol
−1
of C=O = 741; C-H = 414; H-O = 464; O=O = 498.
Q36. The lattice enthalpy of an ionic compound is the enthalpy when one mole of an ionic compound present in its gaseous state, dissociates into
its ions. It is impossible to determine it directly by experiment. Suggest and explain an indirect method to measure lattice enthalpy of
NaCl(s).
Q37. (i) Entropy of vapourisation (a) decreases
(ii) K for spontaneous process (b) is always positive
(iii) Crystalline solid state (c) lowest entropy
ΔHvap
(iv) ΔU in adiabatic expansion of ideal gas (d) Tb
Q38. Enthalpy diagram for a particular reaction is given in Fig. Is it possible to decide spontaneity of a reaction from given diagram. Explain.
Q39. 1.0 mol of a monoatomic ideal gas is expanded from state (1) to state (2) as shown in Fig. Calculate the work done for the expansion of gas
from state (1) to state (2) at 298K.
Q40. What will be the work done on an ideal gas enclosed in a cylinder, when it is compressed by a constant external pressure, pext in a single step
as shown in Fig. Explain graphically.
DAV PS HEHAL DEPT. OF
CHEMISTRY.
Q41. Two moles of an ideal gas initially at 27°C and one atmospheric pressure are compressed isothermally and reversibly till the final pressure of
the gas is 10atm. Calculate q, W and ΔU for the process.
Q42. The heat of combustion of C2H6 is -368.4kcal. Calculate heat of combustion of C2H4, heat of combustion of H2 is 68.32kcal mol-1. ΔH for the
following reaction is -37.1kcal.
−−
→
C2 H4 (g) + H2 (g) C2 H6 (g)
Q43. The combustion of one mole of benzene takes place at 298K and 1atm. After combustion, CO2(g) and H2O(l) are produced and 3267.0kJ of
heat is liberated. Calculate the standard enthalpy of formation of benzene (Δ H ).
f
∘
∘
Δ H CO (g) = −393kJ mol
f 2
−1
and Δ H H O(l) = −285.83kJ mol .
f
∘
2
−1
Q44. Using the data (all values are in kilocalories per mole at 25°C) given below, calculate the bond energy of C-C and C-H bonds.
ΔH combustion (ethane) = -372.0
∘
ΔH combustion (propane) = -530.0
∘
ΔH for C(graphite) → C(g)= 172.0
∘
Bond energy of H-H = 104.0
Δ H of H2O(l) = -68.0
∘
f
ΔH for CO2(g) = -94.0
∘
Q45. 10 moles of an ideal gas expand isothermally and reversibly from a pressure of 5atm to 1atm at 300K. What is the largest mass that can be
lifted through a height of 1m by this expansion?
Q46. What is meant by entropy? Predict the sign of entropy change in each of the following:
1. H2 (at 298K, 1atm) → H2 (at 298K, 10atm)
2. H2O (at 298K, 1atm) → H2O (at 330K, 1atm)
3. 2NH4NO3(s) → 2N2(g) + 4H2O(g) + O2(8)
4. Crystallization of copper sulphate from its saturated solution.
5. 2SO (g) + O (g) ⇌ 2SO (g).
2 2 3
Q47. X(g) + 3Y(g) ⇌ 2Z(g); ΔH = −40kJ and so of X, Y and Z are 60, 40 and 50kJ-1 mol-1 respectively. Calculate the temperature above or
below which reaction become feasible?
Q48. Calculate bond energy of C-H bond if Δ H of CH4, is -891kJ mol-1, Δ H of C(s) is -394kJ mol-1, Δ
c c cH of H2(g) is -286kJ mol-1, heat of
sublimation of C(s) is 717kJ mol-1, heat of dissociation of H2 is 436kJ mol-1.
Q49. Use the following data to calculate Δ H
latticefor NaBr⊖
Δ subH for sodium metal = 108.4kJ mol–1
⊖
Ionization enthalpy of sodium = 496kJ mol–1
Electron gain enthalpy of bromine = –325kJ mol–1
Bond dissociation enthalpy of bromine = 192kJ mol–1
Δf H
⊖
for NaBr (s) = – 360.1kJ mol–1
Q50. 1. State first law of thermodynamics.
2. Heat (q) and work function (w) individually are not state functions but their sum is always a state function. Why?
3. Define extensive property with example.
Q51. Calculate the maximum work obtained when 0.75mol of an ideal gas expands isothermally and reversibly at 27°C from a volume of 15L to
25L.
Q52. Give the appropriate reason.
1. It is preferable to determine the change in enthalpy rather than the change in internal energy.
2. It is necessary to define the 'standard state'.
3. It is necessary to specify the phases of the reactants and products in a thermochemical equation.
Q53. At 298K what will be the change in standard internal energy change for the given reaction:
OF2(g) + H2O(g) → O2(g) + 2HF(g) ΔH = −310kJ
Q54. Taking a specific example, show that ΔS total is a criterion for the spontaneity of a change.
Q55. Will entropy increase or decrease in the following changes?
1. Sugar dissolved in water.
2. Normal egg to hard boiled egg.
DAV PS HEHAL DEPT. OF
CHEMISTRY.
