Enthalpy Change

We are given:

• Enthalpy change ( ) = +40.32 kJ/mol
• Boiling point = 127°C = 400 K
• R = 8.3 J/(mol·K) = 0.0083 kJ/(mol·K)

Use the relation:

In evaporation, 1 mole of liquid becomes 1 mole of gas, so:

Now plug values:

Correct Answer:

+37.0 kJ/mol

The enthalpy of combustion is the heat change when one mole of a substance is completely burnt in excess oxygen under standard conditions.

This is an exothermic process, which means it releases heat to the surroundings.

Therefore, the enthalpy change ( ) is always negative for combustion.

Correct Answer:

Enthalpy of combustion

The first ionisation enthalpy is the energy required to remove the outermost electron from a neutral atom in the gaseous state.

In general, ionisation enthalpy decreases down a group in the periodic table because the atomic size increases and the outer electrons are farther from the nucleus, experiencing less nuclear attraction.

Given elements (all from Group 15 and 16):

• Germanium (Ge)
• Arsenic (As)
• Antimony (Sb)
• Tellurium (Te)
• Bismuth (Bi)

Among these, Bismuth (Bi) is the heaviest and lies lowest in the group. Hence, it has the largest atomic size and the lowest first ionisation enthalpy.

Correct Answer: (E) Bismuth

The combustion of methane (CH ) can be represented by the following balanced chemical equation: The heat liberated during the combustion of methane can be calculated using the standard enthalpy of formation values for the reactants and products. The standard enthalpy change of the reaction is given by: Substituting the values for the standard enthalpy of formation: Thus, the enthalpy change for the combustion of one mole of methane is -890 kJ/mol. Now, we need to calculate the heat released when 3.2 g of methane is burnt. The molar mass of methane (CH ) is: The number of moles of methane in 3.2 g is: The heat released is:

The correct option is (E) :