Unit 3 electrochemical cells and corrosion 8 emf of an electrochemical cell. It includes several features to make your preparation easier. Q is reaction quotient, like equilibrium constant, but not at equilibrium. We can relate this idea of work done in electrochemistry to the thermodynamic concept of work, free energy, through the equation.
These reactions involve electric charges moving between electrodes and an electrolyte or ionic species in a solution. But its value does depend upon the chosen reference state. Electrochemistry example problems ch102 spring 2017. Chemical reactions involving the transfer of electrons from one reactant to another are called oxidationreduction reactions or redox reactions. Electrochemical processes are oxidation reduction reactions. Also corrosion and its prevention is introduced and. In this device the gibbs energy of the spontaneous redox reaction is converted into electrical work which. Electrolytic flow of electrons causes chemistry to occur. In electrochemistry, the quantity in which we are most interested is e, the potential energy of the system. The difference of potential, which causes a current to flow from the electrode of higher potential to the electrode of lower potential, is called the electromotive force e. Lecture 1 5703 5703 simplifying approximations leave out terms involving solids, pure liquids, and solvents solutes appear as the concentration in m.
The nernst equation enables the determination of cell potential under nonstandard conditions. Q has the same form as the equilibrium constant, k. Rtnflnq2 equation 2 can be rewritten in the form of log base 10. Answers to practice test questions 9 redox reactions and. Chemistry notes chemistry pdf chemical equilibrium and. Q can be used to determine which direction a reaction will shift to reach equilibrium. Nernst equation is a general equation that relates the gibbs free energy and cell potential in electrochemistry. It was named after walther nernst, a german physical chemist who formulated. The reaction quotient has the form of the equilibrium constant, except that the concentrations and gas pressures are those that exist in a reaction mixture at a given instant. In electrochemistry, the nernst equation is an equation that relates the reduction potential of an electrochemical reaction halfcell or full cell reaction to the standard electrode potential, temperature, and activities often approximated by concentrations of the chemical species undergoing reduction and oxidation. The reaction quotient, q, is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
Understand what is meant by oxidation, reduction, voltaic cells, and electrolytic cells. Q reaction quotient productreactant relates cell potential and reaction quotient at equilibrium equation. Be able to show and use the relationships between cell potentials and changes in gibbs free energies both standard and nonstandard. Develop an electrochemical series based on potential differences between halfcells. Calculate the equilibrium constant, kc for the reaction.
Oxidation reduction reactions appendix d oxidation. Combining the thermodynamics and the electrochemistry, not to mention a bit of physics. It takes into account the values of standard electrode potentials, temperature, activity and the reaction quotient for the calculation of cell potential. E e o 0592vnlogq the equation above indicates that the electrical potential of a cell depends upon the reaction quotient q of the.
Thus, anything that can be done with or to a free energy change can also be done to or with a cell potential. The work that can be accomplished when electrons are transferred through a wire depends on the push or emf which is defined in terms of a potential difference in volts between two points in the. Q is reaction quotient, like equilibrium constant, but not at equilibrium q actual products reactants. In chemistry it is more common to define chemical potential and other. It relates the measured cell potential to the reaction quotient and allows the accurate determination of equilibrium constants including solubility constants. G is change in gibbs free energy t is absolute temperature r is the gas constant, 8. Reaction quotient q c the mathematical product of the concentrations of the products of the reaction divided by the mathematical product of the concentrations of the reactants. By comparing the value of q to the equilibrium constant, k eq, for the reaction, we can determine whether the forward reaction or reverse reaction will be favored. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
A change in this solution from standardstate conditions ph 0 to the ph of an aqueous ammonia solution ph 11 therefore results in an increase of 0. It is examined via the use of electrochemical cells which are systems that incorporate a redox reaction to produce or utilize electrical energy. Chem 150 answer key problem electrochemistry and thermochemistry 1. The total electrochemical potential of each side of the reaction must be. Petersons master ap chemistry was designed to be as userfriendly as it is complete. This question concerns a concentration cell with positive voltage at 25, constructed from hydrogen half cells of different hydronium ion concentration and sealed so. Electrochemistry is the study of chemical reactions and processes that involve the transfer of. The primary measurement in electrochemistry is the voltage v of an electrochemical cell. I below stands for current in amperes and q for charge in coulombs. As such, when calculating oxidation state, the electrons in the and bonds are all assigned to s along with the four electrons from its lone pairs. Isolated oxidation and reduction processes are not much good. Electrochemistry example problems, ch102 spring 2017, tuesday, april 25, 2017 page 2 problem 2. Electrochemistry and the nernst equation the ccli initiative computers in chemistry laboratory instruction. Introduction to reaction quotient qc video khan academy.
What is the standard free energy change and equilibrium constant for the following reaction at 25 c. The voltage describes the relative energies of electrons on di erent atoms andor ions. If k q, a reaction will proceed forward, converting reactants into products. Electrochemistry some key topics conduction metallic electrolytic electrolysis effect and stoichiometry galvanic cell electrolytic cell electromotive force. The nernst equation is derived from the gibbs free energy under standard conditions. Electrochemistry and the nernst equation learning objectives the objectives of this experiment are to. The reaction quotient \ q\ measures the relative amounts of products and reactants present during a reaction at a particular point in time. The expression for the reaction quotient, q, looks like that used to calculate an equilibrium constant but q can be calculated for any set of conditions, not just for equilibrium. Electrochemistry some key topics conduction metallic electrolytic electrolysis effect and stoichiometry galvanic cell. The cell potential ecell is directly related to the magnitude of the equilibrium constant for the overall oxidationreduction reaction occurring in the. The ushaped glass tube filled with kno 3 connecting the two half cells is called the salt bridge. The nernst equation relates the cell potential at nonstandard conditions to the logarithm of the reaction quotient.
It is an electrochemical cell in which external electrical energy is used to carry out a non spontaneous chemical reaction. Electrochemistry is the study of the relationship between chemical change and electrical work. It is very helpful in determining cell potential, equilibrium constant etc. Introduction to the reaction quotient qc, and comparing the reaction quotient with the equilibrium constant to predict how concentrations will change. Pdf this presentation will help you to become familiar with nernst equation and faraday constant. Remember that a galvanic cell begins with q k, and proceeds until q k. Background any chemical reaction involving the transfer of electrons from one substance to another is an oxidation. Electrochemistry is the branch of physical chemistry that studies the relationship between electricity, as a measurable and quantitative phenomenon, and identifiable chemical change, with either electricity considered an outcome of a particular chemical change or vice versa. Electrical work is the maximum work that the system can produce and so is equal to the change in free energy. Overview each chapter begins with a bulleted overview listing the topics that will be covered in the chapter. Chemical equilibrium section of general chemistry notes is 19 pages in length page 1 through page 19 and covers all youll need to know on the following lecturetextbook topics section chemical equilibrium 1 the equilibrium condition dynamic equilibrium the equilibrium expression the equilibrium constant k. Since the temperature is generally 25 c 298 k, three of the terms in the above nernst equation can be considered constants. By observing the reaction quotient of a voltaic cell, we can define the relationship between emf and equilibrium.
The reaction quotient aids in figuring out which direction a reaction is likely to proceed, given either the pressures or the concentrations of the reactants and the products. Note in equations 1 and 2 that if the reaction quotient is equal to 1, then e. To determine the voltage, we will use the copper reaction as written in the table, but reverse the zinc reaction. Pdf this presentation will help you to become familiar with nernst.
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