Gen Chem 2 Exam 4

+1, -1

the oxidation number of hydrogen is # when combined with nonmetals and is # when combined with metals

-2

the oxidation number of oxygen is # in most compounds

-1, oxygen

the oxidation number for halogens is always # for F and is usually the same for other halogens (except when combined with — or other halogens)

transfer, electrons

a redox reaction is a type of reaction involving the —of —between two species(elements)

Oxidation

the loss of an electron

reduction

gain of an electron

OIL RIG

oxidation is loss (—) reduction is gain (—)

Ag is oxidized, Au is reduced

Ag (s)   +   Au¹⁺ (aq)   ⇌   Ag¹⁺ (aq)   +   Au (s)

Which is oxidized? Which is reduced?

skeletal equations, H, O, water, H, electrons, multiply, simplify

1. Write — —for the oxidation and reduction half-reaction

2. Balance each half reaction for all elements except —and —

3. Balance each half reaction for O by adding as much — as needed

4. Balance each half reaction for — by adding H⁺ as needed

5. Balance each half reaction for charge by adding —

6. If necessary, — one or both half-reactions so that the number of electrons consumed in one is equal to the number produced in the other

7. Add the 2 half-reactions and —

8. USE FOR BASIC SOLUTIONS add OH- ions the equation obtained in the previous step to neutralize the H+ ions and simplify

physical contact, indirect

electrochemical cell: a device that contains the reactants and products of a redox system but prevents — —between the reactants. The transfer of electrons is — and requires an external circuit

spontaneous

Galvanic cell: an electrochemical cell in which a — redox reaction takes place

half cell

— —: contains the redox conjugate pair of a single reactant (2 per galvanic cell)

anode

the cell that contains the oxidation reaction

cathode

the cell that contains the reduction reaction

inert electrolyte, charge

Salt bridge: tube filled with — —solution that connects the anode and the cathode (maintains —balance between the half- cells)

inert electrode

provides or accepts electrons in the redox reaction

active electrode

constructed from a member of the redox reaction

oxidation, reduction

when writing a cell schematic it goes — half-reaction (before|after)||— half-reaction (before|after [unless in same phase then separated by a ,])

Ca(s)|Ca2+(aq)||Co2+(aq)|Co(s)

write a cell schematic of the galvanic cell whose net reaction is: Ca (s) +  Co²⁺ (aq) →  Ca²⁺ (aq)  +  Co (s)

cell potential

(E cell) the difference in potential between 2 half-cells

standard cell potential

(E° cell) the difference in potential between two half-cells measured under standard-state conditions

standard hydrogen electrode

simplified reference for sharing cell potential measurements (SHE) with an assigned potential of 0 volts. Contains a stream of hydrogen gas and occurs at standard-state conditions

electrode potential

the potential measured for a half-cell comprised of X acting as cathode and the SHE acting as anode

standard electrode potential

the potential measured for a half-cell comprised of X acting as a cathode and the SHE acting as the anode when the half-cell X is under standard state conditions

spontaneous

a positive E˚cell (standard cell potential) indicates a — reaction

nonspontaneous

a negative E˚cell (standard cell potential) indicates a — reaction

spontaneous, products

When K>1, G<0, and E>0 a reaction is — under standard conditions and — are more abundant

nonspontaneous, reactants

When K<1, G>0, and E<0 a reaction is — under standard conditions and — are more abundant

at equilibrium, both

When K=1, G=0, and E=0 a reaction is — under standard conditions and — are abundant

identical

Concentration Cells: constructed by connecting 2 nearly — half-cells

galvanic, electrical

Battery: a device consisting of one or more — electrochemical cells that stores and converts chemical energy to — energy to power electrical devices

nonrechargable, dry, alkaline

Primary cells are — and include — cells and — batteries

Dry cell

nonrechargable, use zinc in the container and anode and graphite rod as the cathode

Alkaline battery

non-rechargeable, more efficient than dry cell, uses alkaline electrolytes

NiCd battery

secondary cell that delivers more current and is rechargeable up to 1000x, contains separated cathode and anode plates that are rolled into a case, needs special disposal

Lithium battery

secondary cell that provides a lot of current but is lighter and rechargable, commonly used for personal portable electronics

Lead acid batteries

secondary cell that uses 6 cells that are connected in a series, very common in cars, rechargeable, hazardous, requires proper disposal

fuel cells

galvanic cells that consistently feeds an oxidant to the fuel, doesn't use combustion, doesn’t need to be recharged, used in space crafts

corrosion

degradation of metals by a naturally occurring electrochemical process

paint, alloy, galvanization, cathode protection, sacrificial anode

corrosion prevention methods: (5)

paint

applied to the surface of a metal, prevents surface oxidation of metal

alloy

metallic mix that produces passivation layer

galvanization

coating metal with another more easily oxidized metal

galvanic, active

cathode protection: a — cell is created by making the metal a cathode and connecting it to a more — metal (the sacrificial anode)

electrolysis

the use of electric current to stimulate a non-spontaneous process in a redox system

electroplating

a process using electrolysis to produce a thin coating of metal on a conducting surface

corrosion, aesthetics

electroplating is used for — resistance, strengthening, — purposes, some plated metals include: Ni, Au, Cu

redox

galvanic cells and electrolytic cells both contain cathode/anodes, they cause a transfer of electrons through a — reaction.

nonspontaneous, spontaneous

electrolytic cells require an external power supply in the form of an electric current because the redox reaction in electrolytic cells is — while the redox reaction in galvanic cells is —