Which of the following chemical equations represents a gas-evolution reaction?

• A. Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
• B. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
• C. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
• D. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

Answer: (A)

Verified step by step guidance

1. Understand that a gas-evolution reaction is a chemical reaction in which one of the products is a gas that bubbles out of the solution.
2. Examine each given chemical equation and identify the physical states of the products, focusing on whether any product is a gas (g).
3. For the equation \(\mathrm{Na_2CO_3(aq) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_2O(l) + CO_2(g)}\), note that carbon dioxide (\(\mathrm{CO_2}\)) is produced as a gas, indicating gas evolution.
4. For the other equations, observe that the products are either aqueous (\(\mathrm{aq}\)), liquid (\(\mathrm{l}\)), or solid precipitates (\(\mathrm{s}\)), but no gases are formed.
5. Conclude that the equation producing \(\mathrm{CO_2(g)}\) is the gas-evolution reaction because it releases a gas as a product.