The precipitation reaction between AgNO3(aq) and NaCl(aq) proceeds as follows: AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s). (b) What would you expect for the value of _x001F_H° of the overall molecular equation compared to that for the net ionic equation? Explain.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

검증된 단계별 안내

Identify the overall molecular equation: AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s).

Write the net ionic equation by removing the spectator ions (Na+ and NO3-): Ag+(aq) + Cl-(aq) → AgCl(s).

Understand that the enthalpy change (ΔH°) for a reaction is related to the bonds broken and formed during the reaction.

Recognize that the overall molecular equation includes the formation of NaNO3(aq), which does not occur in the net ionic equation.

Conclude that the ΔH° for the overall molecular equation may differ from the net ionic equation due to the presence of additional processes (e.g., dissolution of NaNO3) in the overall equation.

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions react to form an insoluble solid, known as a precipitate. In this case, AgCl is formed from the reaction of AgNO3 and NaCl. Understanding the formation of precipitates is crucial for predicting the products of reactions and their thermodynamic properties.

Enthalpy Change (_x001F_H°)

Enthalpy change (_x001F_H°) refers to the heat content change during a chemical reaction at constant pressure. It is a key factor in thermodynamics, indicating whether a reaction is exothermic (releases heat) or endothermic (absorbs heat). The overall enthalpy change can differ between the complete molecular equation and the net ionic equation due to the cancellation of spectator ions.

Net Ionic Equations

Net ionic equations represent the actual chemical species that participate in a reaction, excluding spectator ions that do not change during the reaction. This simplification helps in analyzing the essential components of a reaction, particularly in terms of energy changes and reaction mechanisms, which is important for understanding the enthalpy changes associated with the reaction.

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교과서 질문

Consider two solutions, the first being 50.0 mL of 1.00 M CuSO₄ and the second 50.0 mL of 2.00 M KOH. When the two solutions are mixed in a constant-pressure calorimeter, a precipitate forms and the temperature of the mixture rises from 21.5 to 27.7 °C (d) From the calorimetric data, calculate ΔH for the reaction that occurs on mixing. Assume that the calorimeter absorbs only a negligible quantity of heat, that the total volume of the solution is 100.0 mL, and that the specific heat and density of the solution after mixing are the same as those of pure water.

Consider the following acid-neutralization reactions involving the strong base NaOH(aq): HNO31aq2 + NaOH1aq2¡NaNO31aq2 + H2O1l2 HCl1aq2 + NaOH1aq2¡NaCl1aq2 + H2O1l2 NH4+1aq2 + NaOH1aq2¡NH31aq2 + Na+1aq2 + H2O1l2 (d) In the third equation NH4 +1aq2 is acting as an acid. Based on the value of H° for this reaction, do you think it is a strong or a weak acid? Explain.

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교과서 질문

One of the best-selling light, or low-calorie, beers is 4.2% alcohol by volume and a 355-mL serving contains 110 Calories; remember: 1 Calorie = 1000 cal = 1 kcal. To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, C2H5OH, with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix C to determine ΔH for this reaction. (c) If 4.2% of the total volume is ethanol and the density of ethanol is 0.789 g/mL, what mass of ethanol does a 355-mL serving of light beer contain? (d) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the 110 Calories comes from the ethanol?

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