Can you use an approach similar to Hess's law to calculate the change in internal energy, \(\Delta E,\) for an overall reaction by summing the \(\Delta E\) values of individual reactions that add up to give the desired overall reaction?

Short Answer

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Yes, you can use an approach similar to Hess's law to calculate the change in internal energy (\(\Delta E\)) for an overall reaction by summing the \(\Delta E\) values of individual reactions that add up to give the desired overall reaction. This is because both internal energy and enthalpy are state functions and path-independent, allowing their changes to be additive in a manner analogous to Hess's law for enthalpy.

Step by step solution

01

Understand the relationship between internal energy and enthalpy

The relationship between internal energy (\(E\)) and enthalpy (\(H\)) is given by the following equation: \[H = E + PV,\] where \(P\) is pressure, and \(V\) is volume. Both internal energy and enthalpy are state functions, which means their values depend on the initial and final states of the system and not on the path taken to reach those states.
02

Investigate the behavior of internal energy and enthalpy changes under path independence

Internal energy (\(\Delta E\)) is path-independent, and its value depends on the initial and final states of the system. During a reaction, the internal energy can undergo changes due to heat and work exchanges with the surroundings. Similarly, the change in enthalpy (\(\Delta H\)) is also path-independent. Under constant pressure, the change in enthalpy is equal to the heat exchange between the system and its surroundings. Because both internal energy and enthalpy are path-independent, their changes remain constant, regardless of the intermediate steps taken in a reaction. If a reaction occurs in multiple steps, the sum of the changes in internal energy or enthalpy of each step will result in the same change in internal energy or enthalpy for the overall reaction. Therefore, the additive nature of \(\Delta H\) described in Hess's law also applies to \(\Delta E\).
03

Conclude whether Hess's law-like approach is applicable to internal energy

In summary, since both internal energy (\(\Delta E\)) and enthalpy (\(\Delta H\)) are state functions and path-independent, an approach similar to Hess's law can be used to calculate the change in internal energy for an overall reaction by summing the \(\Delta E\) values of individual reactions that add up to give the desired overall reaction.

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Most popular questions from this chapter

(a) When a 4.25 -g sample of solid ammonium nitrate dissolves in 60.0 g of water in a coffee-cup calorimeter (Figure 5.18), the temperature drops from 22.0 to \(16.9^{\circ} \mathrm{C}\) . Calculate \(\Delta H\left(\) in \(\mathrm{kJ} / \mathrm{mol} \mathrm{NH}_{4} \mathrm{NO}_{3}\right)\) for the solution process: $$\mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{NH}_{4}^{+}(a q)+\mathrm{NO}_{3}^{-}(a q)$$ Assume that the specific heat of the solution is the same as that of pure water. (b) Is this process endothermic or exothermic?

Consider the following hypothetical reactions: $$\begin{array}{ll}{\mathrm{A} \longrightarrow \mathrm{B}} & {\Delta H=+30 \mathrm{kJ}} \\ {\mathrm{B} \longrightarrow \mathrm{C}} & {\Delta H=+60 \mathrm{kJ}}\end{array}$$ (a) Use Hess's law to calculate the enthalpy change for the reaction \(A \longrightarrow C .\) (b) Construct an enthalpy diagram for substances \(A,\) and C, and show how Hess's law applies.

(a) Which releases the most energy when metabolized, 1 \(\mathrm{g}\) of carbohydrates or 1 \(\mathrm{g}\) of fat? (b) A particular chip snack food is composed of 12\(\%\) protein, 14\(\%\) fat, and the rest carbohydrate. What percentage of the calorie content of this food is fat? (c) How many grams of protein provide the same fuel value as 25 of fat?

From the enthalpies of reaction $$\begin{aligned} \mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{HF}(g) & \Delta H=-537 \mathrm{kJ} \\ \mathrm{C}(s)+2 \mathrm{F}_{2}(g) \longrightarrow \mathrm{CF}_{4}(g) & \Delta H=-680 \mathrm{kJ} \\ 2 \mathrm{C}(s)+2 \mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g) & \Delta H=+52.3 \mathrm{kJ} \end{aligned}$$ calculate \(\Delta H\) for the reaction of ethylene with \(\mathrm{F}_{2} :\) $$\mathrm{C}_{2} \mathrm{H}_{4}(g)+6 \mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{CF}_{4}(g)+4 \mathrm{HF}(g)$$

The decomposition of \(\mathrm{Ca}(\mathrm{OH})_{2}(s)\) into \(\mathrm{CaO}(s)\) and \(\mathrm{H}_{2} \mathrm{O}(g)\) at constant pressure requires the addition of 109 \(\mathrm{kJ}\) of heat per mole of \(\mathrm{Ca}(\mathrm{OH})_{2}\) . (a) Write a balanced thermochemical equation for the reaction. (b) Draw an enthalpy diagram for the reaction.

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