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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 15th Edition
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Capitolo 5, Problema 76a

Using values from Appendix C, calculate the value of H for each of the following reactions: (a) NiO(s) + 2 HCl(g) → NiCl2(s) + H2O(g)

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Identify the standard enthalpy of formation (\( \Delta H_f^\circ \)) for each compound involved in the reaction from Appendix C.
Write the balanced chemical equation: \( \text{NiO(s)} + 2 \text{HCl(g)} \rightarrow \text{NiCl}_2\text{(s)} + \text{H}_2\text{O(g)} \).
Apply Hess's Law to calculate the enthalpy change (\( \Delta H \)) for the reaction using the formula: \( \Delta H = \sum \Delta H_f^\circ \text{(products)} - \sum \Delta H_f^\circ \text{(reactants)} \).
Substitute the \( \Delta H_f^\circ \) values for each product and reactant into the formula.
Perform the arithmetic operations to find the \( \Delta H \) for the reaction.

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Enthalpy Change (ΔH)

Enthalpy change (ΔH) is the heat content change of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). Calculating ΔH for a reaction often involves using standard enthalpy values from tables, which represent the enthalpy of formation for various substances.
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Enthalpy of Formation

Standard Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. These values are crucial for calculating the overall enthalpy change of a reaction using Hess's law, which states that the total enthalpy change is the sum of the enthalpy changes for individual steps.
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Enthalpy of Formation

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps or the pathway taken. This principle allows chemists to calculate the enthalpy change for complex reactions by breaking them down into simpler steps for which enthalpy values are known, facilitating the calculation of ΔH for the overall reaction.
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Hess's Law
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