CHEM 1010H Lecture Notes - Lecture 3: Electrochemical Cell, Electrochemistry, Reducing Agent

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8 Mar 2018

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Rules for balancing redox reactions: assign oxidation numbers, write out reduction and oxidation half reactions including electrons, complete and balance each half reaction except for. Reduction: a chemical process in which there is a gain of electrons. Reducing agent: causes something else to be reduced, it is oxidized as a result. Oxidizing agent: causes something else to be oxidized, it is reduced as a result. Electrochemical cell: a system consisting of electrodes that are in contact with an electrolyte in which a chemical reaction uses or generates a flow of electrons. Electrodes-> electrons travel from one electrode to another through a wire or something that will help conduct the energy. Voltaic cell: (galvanic cells or batteries) an electrochemical cell in which a spontaneous reaction produces a flow of electrons. Electrolytic cell: an electrochemical cell in which an electric current is used to cause an otherwise non-spontaneous reaction to occur. Separate a single redox reaction into its two half reactions.

Related Questions

Answer true or false.

(a) When a substance is oxidized, it loses electrons.

(b) When a substance gains electrons, it is reduced.

(d) In a redox reaction. the reducing agent becomes oxidized.

(e) When Zn is converted to Zn²⁺ ion, zinc is oxidized.

(f) Oxidation can also be defined as the loss of oxygen atoms and/or gain of hydrogen atoms.

(g) Reduction can also be defined as the gain of oxygen atoms and/or loss of hydrogen atoms.

(h) When oxygen, O₂, is converted to hydrogen peroxide, H₂O₂, we say that O₂ is reduced.

(i) Hydrogen peroxide, H₂O₂, is an oxidizing agent.

(j) All combustion reactions are redox reactions.

(k) The products of complete combustion (oxidation) of hydrocarbon fuels are carbon dioxide, water, and heat.

(l) In the combustion of hydrocarbon fuels, oxygen is the oxidizing agent and the hydrocarbon fuel is the reducing agent.

(m) Incomplete combustion of hydrocarbon fuels can produce significant amounts of carbon monoxide.

(n) Most common bleaches are oxidizing agents.

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Introduction An important type of reaction mechanism is the transfer of electrons from one species to another effecting a change in oxidation state. This gain or loss of electrons is referred to as reduction and oxidation, respectively. For example, consider the two balanced, chemical equations (1 & 2) that follow Cu (s) D Cu (aq) 2e (1) Cl2(aq) 2e D 2Cl (aq) (2) The first equation (1) shows elemental copper metal with a oxidation state of zero forming aqueous copper(Il) ions having an oxidation state of +2. This gain in oxidation number, 0 to +2, is called oxidation. The second equation (2) show elemental chlorine having an oxidation state of zero forming chloride ions in aqueous solution with an oxidation state of This decrease in oxidation number, 0 to -1, is called reduction. In any chemical reaction, the electrons gained or lost are conserved, i.e.. there is no net gain or loss of electrons. In fact, the two reactions illustrated above could occur simultaneously with the electrons lost by copper, gained by the chlorine in aqueous solution. Since the copper provides the electrons that subsequently reduce the chlorine copper is referred to as the reducing agent. Likewise, since the chlorine is accepting the electrons from copper, which subsequently oxidizes the copper, chlorine is referred to as he oxidizing agent. The two reactions above (1 & 2) are called half-reactions, as much as they each constitute one-half of the total reaction Equation 1 is the oxidation half reaction showing Cu(s) losing two electrons. In Equation 2, Cla(aq) gains two electrons and is the reduction half-reaction. If these two half-reaction are added together the result is the total oxidation-reduction reaction or "redox" reaction. Adding the two equations yields (3). Cu(s) Cl2(aq) D Cu (aq) 2CI (aq) (3) Whether or not the above reaction is spontaneous proceeds from reactants to products without input of energy into the system, may be determined by observing the reaction mixture if the reactants and products differ greatly in their appearance. Copper metal is a bright copper color and chlorine in aqueous solution will appear yellow. The Cu ion may turn the liquid part of the mixture blue, however, the Cris colorless and cannot be observed directly. Copper, like many of the transition metals, exhibits a variety of oxidation states depending upon the chemical environment in which it is found. In a strong reducing environment copper may exist as the free metal, Cu(s). An example of such a situation is illustrated in the following chemical equation (4). 4Cuo(s) CH4(g) D 4Cu(s) CO2(g) 2H2O(l) (4)

CHEM 1010H Lecture Notes - Lecture 3: Electrochemical Cell, Electrochemistry, Reducing Agent

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