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Thermodynamics · Question 51

AIPMT 2007MCQEasy📈 Topic in 12% papers+4−1
1

Consider the following reactions: (i) H+(aq) + OH-(aq) H2O(l), H = -X1 kJ mol-1 (ii) H2(g) + 12O2(g) H2O(l), H = -X2 kJ mol-1 (iii) CO2(g) + H2(g) CO(g) + H2O(l), H = -X3 kJ mol-1 (iv) C2H2(g) + 52O2(g) 2CO2(g) + H2O(l), H = +X4 kJ mol-1 Enthalpy of formation of H2O(l) is

  1. +X3 kJ mol-1
  2. -X4 kJ mol-1
  3. +X1 kJ mol-1
  4. -X2 kJ mol-1

Answer

(4) -X2 kJ mol-1

Solution

As per NCERT, the standard enthalpy of formation is the enthalpy change for the formation of one mole of a compound from its elements in their most stable states of aggregation (reference states).

⇒ Only reaction (ii) forms 1 mol of H2O(l) from its elements H2(g) and O2(g).

(i) is neutralisation, (iii) and (iv) have compounds as reactants.

∴ f H [H2O(l)] = -X2 kJ mol-1

Answer: (4)

AIPMT 2007

Keep practising — Thermodynamics

2

Given that bond energies of H-H and Cl-Cl are 430 kJ mol-1 and 240 kJ mol-1 respectively and Hf for HCl is -90 kJ mol-1, bond enthalpy of HCl is

  1. 380 kJ mol-1
  2. 425 kJ mol-1
  3. 245 kJ mol-1
  4. 290 kJ mol-1
AIPMT 2007
3

Identify the correct statement for change of Gibbs energy for a system ( Gsystem) at constant temperature and pressure.

  1. If Gsystem < 0, the process is not spontaneous.
  2. If Gsystem > 0, the process is spontaneous.
  3. If Gsystem = 0, the system has attained equilibrium.
  4. If Gsystem = 0, the system is still moving in a particular direction.
AIPMT 2006
4

Assume each reaction is carried out in an open container. For which reaction will H = E?

  1. 2CO(g) + O2(g) 2CO2(g)
  2. H2(g) + Br2(g) 2HBr(g)
  3. C(s) + 2H2O(g) 2H2(g) + CO2(g)
  4. PCl5(g) PCl3(g) + Cl2(g)
AIPMT 2006
5

The enthalpy and entropy change for the reaction: Br2(l) + Cl2(g) 2BrCl(g) are 30 kJ mol-1 and 105 J K-1 mol-1 respectively. The temperature at which the reaction will be in equilibrium is

  1. 300 K
  2. 285.7 K
  3. 273 K
  4. 450 K
AIPMT 2006
6

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

  1. -358.5 kJ mol-1
  2. -508.9 kJ mol-1
  3. -208.1 kJ mol-1
  4. -269.9 kJ mol-1
AIPMT 2006
7

Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction ?

  1. Exothermic and increasing disorder
  2. Exothermic and decreasing disorder
  3. Endothermic and increasing disorder
  4. Endothermic and decreasing disorder
AIPMT 2005
8

A reaction occurs spontaneously if

  1. T S < H and both H and S are +ve
  2. T S > H and H is +ve and S is −ve
  3. T S > H and both H and S are +ve
  4. T S = H and both H and S are +ve
AIPMT 2005
9

The absolute enthalpy of neutralisation of the reaction : MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l) will be

  1. -57.33 kJ mol-1
  2. greater than -57.33 kJ mol-1
  3. less than -57.33 kJ mol-1
  4. 57.33 kJ mol-1
AIPMT 2005
10

If 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 H2(g) + Br2(g) 2HBr(g) is

  1. -261 kJ
  2. +103 kJ
  3. +261 kJ
  4. -103 kJ
AIPMT 2004
11

Standard enthalpy and standard entropy changes for the oxidation of ammonia at 298 K are -382.64 kJ mol-1 and -145.6 J K-1 mol-1, respectively. Standard Gibbs energy change for the same reaction at 298 K is

  1. -221.1 kJ mol-1
  2. -339.3 kJ mol-1
  3. -439.3 kJ mol-1
  4. -523.2 kJ mol-1
AIPMT 2004

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