To determine the total energy change associated with the dissolution of ammonium nitrate, we need to evaluate the energy required to break the bonds in the solid ammonium nitrate and the energy released when the ions form in solution.
The bond energy of NH4NO3 is given as \( 3040 , \text{kJ/mol} \). When ammonium nitrate dissolves, it forms \( NH4^+ \) and \( NO3^- \).
The bond energies of the resulting ions are:
- \( NH4^+ = 1564 , \text{kJ/mol} \)
- \( NO3^- = 1009 , \text{kJ/mol} \)
To find the total energy change for the reaction, we can use the following formula:
\[ \text{Energy change} = \text{Energy of bonds broken} - \text{Energy of bonds formed} \]
In this case:
\[ \text{Energy change} = \text{(bonds broken)} - \text{(bonds formed)} = 3040 , \text{kJ/mol} - (1564 , \text{kJ/mol} + 1009 , \text{kJ/mol}) \]
Calculating the total energy of the ions formed:
\[ 1564 + 1009 = 2573 , \text{kJ/mol} \]
Now substitute back into the energy change equation:
\[ \text{Energy change} = 3040 , \text{kJ/mol} - 2573 , \text{kJ/mol} = 467 , \text{kJ/mol} \]
Since the energy change is positive, this indicates that the reaction absorbs energy from the surroundings, meaning it is endothermic. As a result, the solution will absorb heat from the environment, causing the surroundings to lose heat.
Thus, the correct answer is:
A. 467 kJ/mol; gain heat.