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Chapter 18: Problem 33

What is a coupled reaction? What is its importance in biological reactions?

Short Answer

Expert verified
A coupled reaction in biological systems is where an energy-releasing (exothermic) reaction happens simultaneously with an energy-requiring (endothermic) reaction, often using ATP hydrolysis as the exothermic reaction. This allows for the powering of processes that wouldn't otherwise occur due to energy requirements. It is fundamental to many crucial physiological processes.

Step by step solution

01

Understanding Coupled Reactions

A coupled reaction is a type of reaction in which an exothermic reaction (one that releases energy) drives an endothermic reaction (one that requires energy to proceed). Often, this involves the hydrolysis of ATP (Adenosine TriPhosphate), a molecule that stores a highly useful form of chemical energy. ATP hydrolysis is exothermic, releasing energy that can be used to power less favorable reactions.
02

Significance of Coupled Reactions in Biological Systems

Coupled reactions are extremely significant in biological systems. The energy released from exothermic reactions like ATP hydrolysis, can 'fuel' simultaneously occurring endothermic reactions, allowing them to proceed when they otherwise wouldn't. This is how cells in our bodies carry out various essential processes that require energy, such as active transport across cell membranes, operating motor proteins, and synthesizing large molecules.

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Most popular questions from this chapter

Comment on the statement: "Just talking about entropy increases its value in the universe."

State whether the sign of the entropy change expected for each of the following processes will be positive or negative, and explain your predictions. (a) \(\mathrm{PCl}_{3}(l)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{PCl}_{5}(s)\) (b) \(2 \mathrm{HgO}(s) \longrightarrow 2 \mathrm{Hg}(l)+\mathrm{O}_{2}(g)\) (c) \(\mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{H}(g)\) (d) \(\mathrm{U}(s)+3 \mathrm{~F}_{2}(g) \longrightarrow \mathrm{UF}_{6}(s)\)

Find the temperatures at which reactions with the following \(\Delta H\) and \(\Delta S\) values would become spontaneous: (a) \(\Delta H=-126 \mathrm{~kJ} / \mathrm{mol}, \Delta S=84 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol}\) (b) \(\Delta H=-11.7 \mathrm{~kJ} / \mathrm{mol}, \Delta S=-105 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol}\).

Use the following data to determine the normal boiling point, in kelvins, of mercury. What assumptions must you make in order to do the calculation? $$ \begin{aligned} \mathrm{Hg}(l): & \Delta H_{\mathrm{f}}^{\circ} &=0 \text { (by definition) } \\\ & S^{\circ} &=77.4 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol} \\ \mathrm{Hg}(g): & \Delta H_{\mathrm{f}}^{\circ} &=60.78 \mathrm{~kJ} / \mathrm{mol} \\ & S^{\circ} &=174.7 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol} \end{aligned} $$

For each pair of substances listed here, choose the one having the larger standard entropy value at \(25^{\circ} \mathrm{C}\). The same molar amount is used in the comparison. Explain the basis for your choice. (a) \(\operatorname{Li}(s)\) or \(\operatorname{Li}(l)\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)\) or \(\mathrm{CH}_{3} \mathrm{OCH}_{3}(l)\) (c) \(\operatorname{Ar}(g)\) or \(\operatorname{Xe}(g)\) (d) \(\mathrm{CO}(g)\) or \(\mathrm{CO}_{2}(g)\) (e) \(\mathrm{O}_{2}(g)\) or \(\mathrm{O}_{3}(g)\) (f) \(\mathrm{NO}_{2}(g)\) or \(\mathrm{N}_{2} \mathrm{O}_{4}(g)\)
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