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Half-reaction
the oxidation or reduction part of a reaction considered alone
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In an equation for an oxidation half reaction the electrons released always appear on the _____ side of the arrow. Their state is not given because they are in ______ and do not have a definitive physical state.
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The reduced and oxidized species in a half reaction jointly form a ______ ______.
Redox couple
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Reduction half reactions represent the electron ____ with the electron on the _____ side of the arrow.
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Steps of balancing complicated redox reactions (10) story:
- We want to balance the half reactions 1st, then combine them.
- Identify the species being oxidized and the species being reduced from the changes in their oxidation numbers
- Write the two skeletal (unbalanced) equations for the oxidation and reduction half-reactions
- Balance all elements in the half-reactions except O and H.
- IF solution is acidic, balance O by using H2O and then balance H by using H+.
- IF solution is basic, balance O with H2O; then balance H by adding one H2O for every H to the side of each half-reaction that needs H and adding the same number of OH- to the other side.
- Cancel like species
- Balance the electric charges by adding electrons to the left for reductions and to the right for oxidations until the charges on the two sides of the arrow are the same
- If necessary, multiply each half-reaction by the factor required to give equal numbers of electrons in the two half-reactions, and add the two equations and include physical states.
- Finally, cancel out like species appearing on both sides of the arrow and check to make sure that charges as well as numbers of atoms balance
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An electrochemical cell is a device in which an _______ ______, a flow of electrons through a _______, is either produced by a ________ chemical reaction or used to bring about a __________ reaction
- electrical current
- circuit
- spontaneous
- nonspontaneous
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A galvanic cell or a ______ cell is an electrochemical cell in which a ________ chemical reaction is used to generate an ______ _____.
- voltaic
- spontaneous
- electric current
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A battery is a collection of ______ _____ joined in series, so the voltage that it produces, its ability to push an electric current through a ______, is the sum of the ______ of the cell.
- galvanic cell
- circuit
- voltages
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Voltaic cells consist of two _______, or metallic conductors, which make ______ contact with the contents of the cell but not with _____ ______ and one _________, which is an ionically conducting medium
- electrodes
- electrical
- each other
- electrolyte
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We can think of the overall chemical reaction of a galvanic cell as pushing _______ to one electrode (from the other electrode) through the ________ process taking place there and pulling them off the other electrode from the ________ taking place there.
- electrons
- oxidation
- reduction
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The electrode at which oxidation takes place is called the _______ (marked with a ____ sign) and the electrode at which reduction takes place is called the ________ marked with a ____ sign
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In a voltaic cell, a spontaneous chemical reaction draws ______ into the cell through the cathode, the site of ______, and releases them at the anode, the site of ______.
- electrons
- reduction
- oxidation
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Electrochemical reactions can either have a lot of pushing/pulling power, generating high potential differences aka _____ _____ or the opposite where they generate low potential differences aka _____ _____.
- high voltages
- low voltages
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An exhausted battery is one that has lost all power to push/pull electrons and can no longer generate ________ ______. Such batteries are said to be in ________.
- potential differences
- equilibrium
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The SI unit of potential and potential difference is the _____ (_). Using this unit, what would you say the potential difference of a dead battery is? Explain how we can use this unit to form pure energy in joules
- volt (V)
- 0V
- When the charge of one coulomb falls through the potential difference of one volt, a joule is released, in other words: 1C * 1V = 1 J
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Electrical work is a type of _______ work because it involves moving electrons rather than changing the volume of the system. At constant temperature and pressure, the maximum ________ work that is system can do is equal to the change in ______ _____ energy.
- nonexpansion work
- nonexpansion work
- Gibbs free energy
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The work done when an amount (n or in moles) of electrons travels through a potential difference (E), is their total charge times potential difference. The charge of one electron is ___; the charge per mole of electrons is ____. Therefore the total charge is ____. So we=? (2)
- e-
- e-NA-neNAwe = total charge * potential difference = (-neNA) * E
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Faraday's constant (F), is the magnitude of the charge per mole of electrons. This is the product of the elementary charge (__) and ________ ______ (__). We could say F = ____ = 9.6485 * 104 C⋅(mol e-)-1
- e-
- Avogradro's number (NA)
- e⋅NA
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State the intermediate step and the resulting formula that allows us to combine the thermodynamic equation relating Gibbs free energy and nonexpansion work (also state the units of ΔG):
- we (work done by electrons) = -nFE
- ΔG = -nFE
- Joules or kilojoules
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In the equation ΔG = -nFE, what is the significance of n
the number of moles of electrons transferred
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Interpret the equation ΔG = -nFE in its molar form where n is interpreted as a pure number. What is the difference in ΔG?
- ΔGr = -nrFE
- ΔGr is now in Joules or kilojoules per mole
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If the potential difference (E) is positive, then the reaction Gibbs free energy is ______, and the cell reaction has a ______ tendency to form ______. If E is negative, then the reverse of the cell reaction is ________, and the cell reaction has a ________ tendency to form ______
- negative
- spontaneous
- products
- spontaneous
- spontaneous
- reactants
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When we use a voltmeter with such a high resistance that the potential difference is measured without drawing any current, the potential difference (Ecell) becomes the maximum potential that can be produced, this is called the _____ _____ or _______ force
cell potential or electromotive force
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