Oxidation-Reduction Reactions That Require Electrical Energy

5 Oxidation-Reduction Reactions That Require Electrical Energy 

When we look at the activity series in Table 15.3, we see that the oxidation of Cu is below Zn. This means that the following oxidation-reduction reaction is not spontaneous  

Describe the half-cell reactions and the overall reactions that occur in electrolysis. 

FIGURE 15.5 In this electrolytic cell, the Cu anode is in a Cu solution, and the Zn cathode is in a Zn solution. Electrons provided by a battery reduce Zn + to Zn and drive the oxidation of Cu to Cu at the Cu anode. 

Q Why is an electrical current needed to make the reaction of Cu(s) and Zn +(aq) happen  

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Oxidation-Reduction Reactions Oxidation Numbers Balancing Oxidation-Reduction Equations Using Half-Reactions Electrical Energy from Oxidation-Reduction Reactions Oxidation-Reduction Reactions That Require Electrical Energy Oxidation of Alcohols Extended Topic... 

OXIDATION-REDUCTION REACTIONS THAT REQUIRE ELECTRICAL ENERGY 543... 

We learn much about chemical reactions from the study of electrochemistry. The amount of electrical energy consumed or produced can be measured quite accurately. All electrochemical reactions involve the transfer of electrons and are therefore oxidation-reduction reactions. The sites of oxidation and reduction are separated physically so that oxidation occurs at one location, and reduction occurs at the other. Electrochemical processes require some method of introducing a stream of electrons into a reacting chemical system and some means of withdrawing electrons. In most applications the reacting system is contained in a cell, and an electric current enters or exits by electrodes. 

Since the reactant and/or the product are charged species, the fact that the electrical potential in the solution and at the reaction site is not the same leads to the introduction of work terms wr = z.a(P2 for the reactants and w p = (za + n) for products (n = 1 for oxidations, n = — 1 for reductions), which measure the free energy required to bring the reactant and the product, respectively, from the bulk of the solution to the reaction site. 

Chapter 17 emphasizes the principles associated with obtaining electrical energy from electron-transfer reactions in solution. This chapter emphasizes what happens when electrical energy is applied to solutions in the operation of electrolytic cells. The oxidation and reduction processes that take place in an electrolytic cell are called electrolysis. We focus on determining what products are obtained and how much energy is required. 

In an electrochemical cell a redox reaction occurs in two halves (see Topic B4). Electrons are liberated by the oxidation half reaction at one electrode and pass through an electrical circuit to another electrode where they are used for the reduction. The cell potential E is the potential difference between the two electrodes required to balance the thermodynamic tendency for reaction, so that the cell is in equilibrium and no electrical current flows. E is related to the molar Gibbs free energy change in the overall reaction (see Topic B3) according to... 

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