Which of the following is the balanced net-ionic equation for the reaction between Li(s) and water? — Stoichiometry Chemistry Question

STEPS:

1. Identify the reactants and products of the molecular reaction: Lithium metal ($\text{Li}(s)$) reacts with liquid water ($\text{H}_2\text{O}(l)$) to produce aqueous lithium hydroxide ($\text{LiOH}(aq)$) and hydrogen gas ($\text{H}_2(g)$). The balanced molecular equation for this reaction is:
$$2\ \text{Li}(s) + 2\ \text{H}_2\text{O}(l) \rightarrow 2\ \text{LiOH}(aq) + \text{H}_2(g)$$
2. Classify each reactant and product to determine if it dissociates: In net-ionic equations, soluble strong electrolytes (like strong bases and highly soluble ionic salts) are written in their dissociated ionic forms, while solids, liquids, gases, and weak electrolytes are kept in their undissociated molecular forms:
* $\text{Li}(s)$: A solid metal element, so it is kept in its metallic solid form: $\text{Li}(s)$.
* $\text{H}_2\text{O}(l)$: A pure molecular liquid and very weak electrolyte, so it is kept in its molecular liquid form: $\text{H}_2\text{O}(l)$.
* $\text{LiOH}(aq)$: A strong base and highly soluble ionic compound, meaning it completely dissociates in water into its aqueous ions: $2\ \text{Li}^+(aq) + 2\ \text{OH}^-(aq)$.
* $\text{H}_2(g)$: A molecular gas, so it is kept in its molecular gas form: $\text{H}_2(g)$.
3. Write the total ionic equation: Substitute the dissociated forms of the strong electrolytes back into the balanced molecular equation:
$$2\ \text{Li}(s) + 2\ \text{H}_2\text{O}(l) \rightarrow 2\ \text{Li}^+(aq) + 2\ \text{OH}^-(aq) + \text{H}_2(g)$$
4. Identify and remove spectator ions: Spectator ions are ions that appear in identical forms on both the reactant side and the product side of the equation. Since there are no free ions on the reactant side to cancel out, there are no spectator ions in this reaction.
5. Confirm mass and charge balance for the final equation: The resulting net-ionic equation is:
$$2\ \text{Li}(s) + 2\ \text{H}_2\text{O}(l) \rightarrow 2\ \text{Li}^+(aq) + 2\ \text{OH}^-(aq) + \text{H}_2(g)$$
* Mass check: There are 2 Li, 4 H, and 2 O atoms on both sides.
* Charge check: The net charge on the reactant side is 0, and the net charge on the product side is also 0 ($2(+1) + 2(-1) = 0$).
This confirms that Option B is the correct, balanced net-ionic equation.

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WHY_OTHERS_WRONG:

• Option A is incorrect: This equation represents the liquid water reactant as dissociated $\text{H}^+(aq)$ and $\text{OH}^-(aq)$ ions. Because water is a molecular liquid and a weak electrolyte, it must be written in its molecular form, $\text{H}_2\text{O}(l)$. Additionally, it incorrectly includes spectator hydroxide ions on both sides.
• Option C is incorrect: This option represents lithium hydroxide as a solid precipitate, $\text{LiOH}(s)$. Because lithium hydroxide is highly soluble in water and is a strong base, it must be represented in its dissociated, aqueous ionic state as $\text{Li}^+(aq)$ and $\text{OH}^-(aq)$.
• Option D is incorrect: This option incorrectly identifies the product of the reaction as solid lithium hydride, $\text{LiH}(s)$. Alkali metals react with water to yield basic hydroxides and hydrogen gas, not metal hydrides.