Thermodynamics · Question 67

AIPMT 2003MCQEasy📈 Topic in 12% papers+4−1

For which one of the following equations is H react equal to H f for the product ?

Xe(g) + 2F2(g) XeF4(g)
2CO(g) + O2(g) 2CO2(g)
N2(g) + O3(g) N2O3(g)
CH4(g) + 2Cl2(g) CH2Cl2(l) + 2HCl(g)

Answer

(1) Xe(g) + 2F2(g) XeF4(g)

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 (reference states).

(1) One mole of XeF4 is formed from Xe(g) and F2(g), both elements in their standard states ⇒ H react = H f(XeF4).

(2) CO is a compound and 2 mol of product are formed.

(3) O3 is not the stable form of oxygen (O2 is).

(4) The reactant CH4 is a compound and two products are formed.

Answer: (1)

AIPMT 2003

Keep practising — Thermodynamics

The molar heat capacity of water at constant pressure, C, is 75 J K-1 mol-1. When 1.0 kJ of heat is supplied to 100 g of water which is free to expand, the increase in temperature of water is

1.2 K
2.4 K
4.8 K
6.6 K

AIPMT 2003

Unit of entropy is

J K-1 mol-1
J mol-1
J-1 K-1 mol-1
J K mol-1

AIPMT 2002

In a closed insulated container a liquid is stirred with a paddle to increase the temperature. Which of the following is true?

E = W 0, q = 0
E = W = q 0
E = 0, W = q 0
W = 0, E = q 0

AIPMT 2002

Heat of combustion Ho for C(s), H2(g) and CH4(g) are -94, -68 and -213 kcal/mol, then Ho for C(s) + 2H2(g) CH4(g) is

-17 kcal
-111 kcal
-170 kcal
-85 kcal

AIPMT 2002

2 moles of an ideal gas at 27 temperature is expanded reversibly from 2 lit. to 20 lit. Find entropy change. (R = 2 cal/mol K)

92.1
0
4
9.2

AIPMT 2002

Change in enthalpy for reaction, 2H2O2(l) 2H2O(l) + O2(g) if heat of formation of H2O2(l) and H2O(l) are -188 and -286 kJ/mol respectively, is

-196 kJ/mol
+196 kJ/mol
+948 kJ/mol
-948 kJ/mol

AIPMT 2001

When 1 mol of gas is heated at constant volume temperature is raised from 298 to 308 K. Heat supplied to the gas is 500 J. Then which statement is correct ?