Question

In the equilibrium reaction ${N_2} + 3{H_2} \Leftrightarrow 2N{H_3}$, the sign of $\Delta H$ accompanying the reaction is,
A) Positive.
B) Negative.
C) May be positive or negative.
D) Cannot be predicted.

Answer 1

Hint:First, we see what enthalpy of a reaction is.
Enthalpy:
The heat of reaction or the enthalpy change is defined because the energy absorbed or released in any reaction.

Complete step by step answer:If energy is absorbed by the reaction it is claimed to be endothermic and is positive and more energy is required to interrupt the bonds and therefore the reactants are lower in energy than the products.
If energy is released by the reaction is claimed to be exothermic and is negative and more energy is released while forming bonds and therefore the energy of the merchandise is less than the reactants.
The formation of ammonia is associated with \[ - 92.2kJ\] loss of energy. Thus the reaction is exothermic and the sign of ΔH is negative, i.e. \[\Delta H = - 92.2kJ\].
Therefore option B is correct.


Note: Now we discuss about the enthalpy of fusion and enthalpy of vaporization
Enthalpy of fusion:
The solid absorbs a heat and melts is called the enthalpy of fusion or heat of fusion and is sometimes quoted on a molar basis. For instance, when \[1mol\] of ice is melted, we discover the molar enthalpy of fusion of ice is \[ + 6.01kJmo{l^{-1}}\], and we can write that as,
${H_2}O\left( s \right)\xrightarrow{{{0^ \circ }C}}{H_2}O\left( l \right)$
$\Delta {H_m} = 6.01kJ/mol$
Enthalpy of Vaporization:
When a liquid is boiled, the difference of temperature with the heat supplied is analogous to it found for melting. When heat is supplied at a mild rate to a liquid at atmospheric pressure, the temperature rises until the boiling point is attained. After the boiling point the temperature remains constant until the enthalpy of vaporization is supplied and again the temperature rises once all the liquid has been converted to vapor.