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Chapter 17: Problem 4

What types of experiments can be carried out to determine whether a reaction is spontaneous? Does spontaneity have any relationship to the final equilibrium position of a reaction? Explain.

Short Answer

Expert verified
To determine whether a reaction is spontaneous, experiments can involve observation, measuring temperature changes, and calculating the change in Gibbs free energy (ΔG) from experimental measurements. The spontaneity of a reaction is not directly related to its final equilibrium position. However, spontaneous reactions tend to move towards equilibrium, where ΔG becomes zero. The reaction may reach equilibrium before all reactants are converted to products.

Step by step solution

01

Understanding Spontaneity

Spontaneity in chemical reactions refers to whether a reaction will occur without the input of external energy. Spontaneous reactions are typically driven by the decrease in enthalpy (heat content) and/or an increase in entropy (disorder) of the system.
02

Gibbs Free Energy and Spontaneity

The spontaneity of a reaction can usually be determined by calculating the change in Gibbs free energy (ΔG). The equation for ΔG is given by: ΔG = ΔH - TΔS where ΔH is the change in enthalpy, T is the temperature in kelvin, and ΔS is the change in entropy. If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is non-spontaneous. If ΔG is zero, the reaction is in equilibrium.
03

Experimental Methods for Determining Spontaneity

There are several ways to experimentally determine if a reaction is spontaneous: 1. Observation: If a reaction happens without needing an external energy source, it's most likely spontaneous. 2. Measuring temperature changes: If the reaction is exothermic (releases heat), it is more likely to be spontaneous. Conversely, if the reaction is endothermic (absorbs heat), it may not be spontaneous. 3. Calculating ΔG from experimental measurements: Using experimental data to determine ΔH and ΔS, the value of ΔG can be calculated. If ΔG is negative, the reaction is spontaneous.
04

Relationship between Spontaneity and Equilibrium

The final equilibrium position of a reaction is not directly determined by the spontaneity of the reaction. However, there is a connection between the two, as spontaneous reactions tend to move towards equilibrium. At equilibrium, the forward and reverse reactions occur at the same rate, and ΔG becomes zero. Keep in mind that a spontaneous reaction doesn't necessarily imply that the reaction will go to completion, as it may reach equilibrium before all reactants are converted to products.

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Most popular questions from this chapter

Many biochemical reactions that occur in cells require relatively high concentrations of potassium ion \(\left(\mathrm{K}^{+}\right)\). The concentration of \(\mathrm{K}^{+}\) in muscle cells is about \(0.15 M\). The concentration of \(\mathrm{K}^{+}\) in blood plasma is about \(0.0050 M .\) The high internal concentration in cells is maintained by pumping \(\mathrm{K}^{+}\) from the plasma. How much work must be done to transport \(1.0 \mathrm{~mol} \mathrm{~K}^{+}\) from the blood to the inside of a muscle cell at \(37^{\circ} \mathrm{C}\), normal body temperature? When \(1.0 \mathrm{~mol} \mathrm{~K}^{+}\) is transferred from blood to the cells, do any other ions have to be transported? Why or why not?

Consider two reactions for the production of ethanol: $$\begin{array}{l}\mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l) \\\ \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l)+\mathrm{H}_{2}(g) \end{array}$$ Which would be the more thermodynamically feasible at standard conditions? Why?

The synthesis of glucose directly from \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) and the synthesis of proteins directly from amino acids are both nonspontaneous processes under standard conditions. Yet it is necessary for these to occur for life to exist. In light of the second law of thermodynamics, how can life exist?

A green plant synthesizes glucose by photosynthesis, as shown in the reaction $$6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g)$$ Animals use glucose as a source of energy: $$\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g) \longrightarrow 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l)$$ If we were to assume that both these processes occur to the same extent in a cyclic process, what thermodynamic property must have a nonzero value?

Given the following data: $$\begin{aligned}2 \mathrm{H}_{2}(g)+\mathrm{C}(s) \longrightarrow \mathrm{CH}_{4}(g) & & \Delta G^{\circ}=-51 \mathrm{~kJ} \\ 2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{O}_{2}(g) & \Delta \mathrm{H}_{2} \mathrm{O}(l) & & \Delta G^{\circ}=-474 \mathrm{~kJ} \\ \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) & \Delta G^{\circ} &=-394 \mathrm{~kJ}\end{aligned}$$ Calculate \(\Delta G^{\circ}\) for \(\mathrm{CH}_{4}(\mathrm{~g})+2 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(l) .\)
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