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Chapter 52: Problem 2

Gaseous sodium ions and gaseous chloride ions will combine to form solid sodium chloride. a) Which is the lower energy state: 1 mole of \(\mathrm{NaCl}(\mathrm{s})\) or \(1 \mathrm{~mole}\) of \(\mathrm{Na}^{+}(\mathrm{g})\) and 1 mole of \(\mathrm{Cl}^{-}(\mathrm{g})\) ? b) Is \(\Delta H\) for the process \(\mathrm{Na}^{+}(\mathrm{g})+\mathrm{Cl}^{-}(\mathrm{g}) \rightleftharpoons \mathrm{NaCl}(\mathrm{s})\) positive, negative, or zero? c) Why doesn't a salt crystal suddenly become gaseous sodium ions and gaseous chloride ions?

Short Answer

Expert verified
a) 1 mole of \(NaCl(s)\) is the lower energy state.\nb) The \(\Delta H\) for the process is negative.\nc) A salt crystal doesn't spontaneously change into gaseous ions due to its stability in solid state and the high energy required for such transformation.

Step by step solution

01

Part A: Identifying Lower Energy State

In chemistry, the system with the lowest possible energy state is considered the more stable one. Comparing the energy states of 1 mole of \(NaCl(s)\) and 1 mole each of \(Na^{+}(g)\) and \(Cl^{-}(g)\), the solid state sodium chloride (\(NaCl(s)\)) is of lower energy, hence more stable. This is because ionic bonds form between sodium ions and chloride ions in solid state sodium chloride, which is energetically advantageous and leads to a more stable, lower energy state.
02

Part B: Determining \(\Delta H\) for The Process

\(\Delta H\), also known as the change in enthalpy, represents the heat content of a system. It is often used to describe the energy change in chemical reactions. Here, \(\Delta H\) for the process \(Na^{+}(g) + Cl^{-}(g) \rightleftharpoons NaCl(s)\) is negative. During this reaction, as the ions come together to form an ionic solid (sodium chloride), energy is released, making the reaction exothermic. An exothermic reaction corresponds to a negative \(\Delta H\) value.
03

Part C: Explaining Stability of Salt Crystals

A salt crystal, such as sodium chloride, is incredibly stable and doesn't spontaneously change into its gaseous ionic constituents due to its lower energy state as a solid (as explained in part a). Additionally, this transformation would require a substantial amount of energy, such as heat, to break the ionic bonds in the crystal lattice structure, which in typical conditions is not readily available.

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Most popular questions from this chapter

Is it possible to determine whether a process will occur naturally solely by examining the sign of \(\Delta H\) for the process? Explain.

A ball tends to roll down a hill. a) Which is the lower energy state: the ball at the top of the hill or the ball at the bottom of the hill? b) Is the change in the potential energy for this process, \(V_{\mathrm{f}}-V_{\mathrm{i}}\), positive, negative, or zero? c) Why doesn't the ball roll up the hill?

Is \(\Delta S\) for the following process positive or negative? Why? \(\mathrm{C}_{4} \mathrm{H}_{8}(\mathrm{~g} ; 298 \mathrm{~K} ; 1 \mathrm{~atm}) \rightleftharpoons \mathrm{C}_{4} \mathrm{H}_{8}(\mathrm{~g} ; 298 \mathrm{~K} ; 0.5 \mathrm{~atm})\)

Write a chemical equation that describes the melting of ice, and indicate whether \(\Delta H\) for the process is positive, negative, or zero. Under what temperature conditions does this process naturally occur?

Is \(\Delta S\) for the following process positive or negative? Why? \(\mathrm{C}_{4} \mathrm{H}_{8}(\mathrm{~g} ; 298 \mathrm{~K} ; 1 \mathrm{~atm}) \rightleftarrows \mathrm{C}_{4} \mathrm{H}_{8}(\mathrm{~g} ; 398 \mathrm{~K} ; 1 \mathrm{~atm})\)
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