(a) <span>Δ<span>Hproducts</span>>Δ<span>Hreactants</span></span>; (b) endothermic; (c) ionic bonds between <span>NH<span>+4</span></span> and <span>NO<span>-3</span></span>.
Explanation:
<span>(a) Enthalpy of formation of reactants and products</span>
We have the reaction
<span><span>Mr</span><span>/g⋅mol-1</span><span>mmmll</span>80.04</span>
<span><span>mmmmmmmm</span><span>NH4</span><span>NO3</span>(s)⇌<span>NH<span>+4</span></span>(aq)+<span>NO<span>-3</span></span>(aq)</span>
<span><span>Δf</span><span>H∘</span><span>/kJ⋅mol-1</span>m-365.1<span>mmmm</span>-132.8<span>mmm</span>-206.6</span>
<span><span>Δf</span><span>H<span>∘reactants</span></span>=-365.1 kJ.mol</span>
<span><span>Δf</span><span>H<span>∘products</span></span>=(-132.8 - 206.6) kJ=-339.4 kJ/mol</span>
<span><span><span>Moles of NH4</span><span>NO3</span>=10.0<span><span>g NH4</span><span>NO3</span></span>×<span><span><span>1 mol NH4</span><span>NO3</span></span><span>80.04<span><span>g NH4</span><span>NO3</span></span></span></span></span><span>=<span>0.1249 mol NH4</span><span>NO3</span>=0.1249 mol reaction</span></span>
<span>Δ<span>Hreactants</span>=0.1249mol reaction×<span>-365.1 kJ<span>1mol reaction</span></span>=-45.6 kJ</span>
<span>Δ<span>Hproducts</span>=0.1249mol reaction×<span>-339.4 kJ<span>1mol reaction</span></span>=-42.4 kJ</span>
∴ <span>Δ<span>Hproducts</span>>Δ<span>Hreactants</span></span>
(b) Exothermic or endothermic?
The temperature decreased when the ammonium nitrate dissolved in the water.
Energy left the system, so the reaction is endothermic.
(c) Bonds broken
The ionic bonds between the <span>NH<span>+4</span></span> ions and <span>NO<span>-3</span></span> ions were broken when the ammonium nitrate dissolved in the water.