Unit 4: Electrochemistry Flashcards by Salina H Huy

Electrochemistry

the study of the movement of electrons from one chemical species to another in chemical reactions

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Electrochemistry is the study of chemical reactions that ________ electricity and chemical reactions that can be carried out by _____________

give off, running electricity through them

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Oxidation-reduction (redox) chemistry is the study of the movement of electrons from __________ in chemical reactions

one atom to another

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All electrochemical reactions involve…

the transfer of electrons from one atom to another

Sometimes when the electron(s) are transferred a bond is formed between the two atoms, and sometimes the electrons are transferred with no bond forming between the atoms.

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when assigning oxidation numbers we’re going to treat every compound as if it were an _______ compound even when we know it’s not. There are no ____________ when assigning oxidation numbers.

ionic, “shared electrons”

each electron belongs entirely to one atom or to another atom.

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Any atom in a neutral element has an oxidation number of _______.

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A neon atom (Ne) has an oxidation number of ________, and so do both atoms in an H2 molecule.

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The oxidation state of any monatomic ion is equal to the _________ on the ion.

charge

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Na+ and H+ both have an oxidation number of _________.

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In a neutral compound the oxidation numbers of all the atoms in the compound add up to _____

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Each H atom in H2O is in a ___ oxidation state and the oxygen is __.

+1, –2
These add up to 0.

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in a polyatomic ion the oxidation numbers of all the atoms in the polyatomic ion add up to the __________.

charge on the ion

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In a hydroxide ion, OH–, the oxygen is in a __ oxidation state and the hydrogen is __.

–2, +1

adding up to the charge on the ion, 1–.

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In compounds hydrogen almost always has an oxidation number of __

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In compounds oxygen almost always has an oxidation number of __.

-2

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elements H2 and O2, the oxidation numbers are __.

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When hydrogen appears at the end of a compound formula that _________, that hydrogen is in a __ oxidation state. This type of compound is called a ____________.

begins with a metal, –1, metal hydride

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There are only two metal hydrides that you might see in this class:

Lithium aluminum hydride, LiAlH4, and sodium borohydride, NaBH4.

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When oxygen is in a compound called a peroxide, the O atoms are both __.

–1

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The most common peroxide and the only one you’ll see in this class is…

hydrogen peroxide, H2O2 (H-O-O-H)

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Halogens are always __ in compounds unless they are bonded to _______, in which case their oxidation state will depend on how many ________ they are bonded to.

–1, oxygen, oxygens

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in NaClO4 the oxidation number of the Cl atom is __.

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What is the oxidation number of the manganese in Mn3(PO4)2?

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Anytime you see a phosphate ion the phosphorus atom will be in a __ oxidation state.

+5
PO43-

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Redox reactions

reactions in which atoms undergo a change in oxidation number by exchanging one or more electrons from one atom to another

If any atom's oxidation state changes from the reaction side to the product side, that means it is ___________ during the reaction, and the reaction is a ____________.

gaining or losing electrons, redox reaction

Oxidation is the ____ of electrons

loss

Anything that loses electrons is said to be ________, and its oxidation number __________.

oxidized, increases (becomes more positive)

Reduction is the ____ of electrons.

gain

Anything that gains electrons is said to be _______, and its oxidation number ____________.

reduced, decreases (becomes more negative)

If something in a chemical reaction is oxidized, something else in the reaction must be ________.

reduced

Sn (s) + 2HCl (aq) ⟶ SnCl2 (aq) + H2 (g) This _________ a redox reaction. __ is being oxidized and __ is being reduced.

is, Sn, H

The reactant that is providing the electrons is called the ___________.

reducing agent

The reactant that is taking the electrons away is called the ____________.

oxidizing agent

LEO says GER

Lose Electrons Oxidation Gain Electrons Reduction

The activity series is a list of...

metal oxidation half-reactions list that ranks metals by how easily they give up their electrons

Higher up in the activity series means a metal is more...

easily oxidized in a chemical reaction higher free energy more reactive strongest reducing agents ("want" to give up their electrons)

Activity table: When you draw a connecting line from the metal to the ion, if the line goes down that means the reaction _____________.

will be spontaneous electrons experienced a negative ΔG, which means a spontaneous process.

Activity table: If when you connected the metal to the ion your line had to go up, that would be a ___________ reaction.

nonspontaneous

Since each beaker contains half of the reactants and half of the products of the overall reaction, we say that each of the beakers is a ___________.

half-cell

A chemical reaction that produces electricity would be

spontaneous

The electrode where oxidation occurs (where the electrons are coming from) is called the _________.

anode

The electrode where reduction occurs (where the electrons are headed) is called the __________.

cathode

No matter how the cell diagram is drawn, in the shorthand notation the _________ always goes on the left and the _________ goes on the right.

anode, cathode

Although it works exactly the same way as the activity series, the table of standard reduction potentials looks a little different. The half-reactions are written as _________ instead of as _________ as they were in the activity series, and the most easily oxidized species are at the ________ of the standard reduction potentials table instead of at the _________.

reductions, oxidations bottom, top

table of standard reduction potentials: If your line goes down and to the right, that's a _________reaction and it generates a _______________.

spontaneous, positive potential (positive voltage)

If we're talking about a cell potential under standard conditions, we call it __________

E° ("E-zero")

E° ("E-zero") formula:

E°cell = E°reduction – E°oxidation

If your calculated E°cell is positive, that means your cell __________. This kind of cell is called a ____________.

gives off electricity galvanic cell or a voltaic cell

If your calculated E°cell is negative, that means your reaction is __________. This kind of cell is called an ____________.

nonspontaneous electrolytic cell in order to make the reaction go in the forward direction you would have to put in electricity into it.

oxidation always occurs at the ________ and reduction always occurs at the ________. A common mnemonic for this is __________________.

anode, cathode ANode OXidation and REDuction CAThode

in a galvanic cell the cathode is ________ and the anode is ________

positive, negative

In an electrolytic cell the cathode is _________ and the anode is _________.

negative, positive

In an galvanic cell, Ecell is (_) and ΔG is (_).

+, –

In an electrolytic cell, Ecell is (_) and ΔG is (_)

-, +

charge =

Current × time (in seconds)

ΔG° = –(charge × ___________) = –(charge × __________)

voltage, E°cell

C =

96485 C/mol × moles

oxidation state of each atom? I3-

-1/3

ammonia

NH3

ammonium

NH4+

_________ reactions and __________ reactions are not redox reactions because electrons ___________

Acid-base, precipitation do not move from one species to another in these reactions.

primary batteries

Batteries that are not rechargeable

secondary batteries

Batteries are rechargeable

Steps for Balancing Redox Equations using the Half-Reaction Method

1. Balance the main atom. 2. Add H2O to balance oxygen. 3. Add H+ to balance hydrogen. Add same # of OH- to both sides in basic solution and cancel out. 4. Balance the charge using electrons.

Without an external power supply to force the reaction to run in reverse (electrolytic cell), the ____________ reaction will occur.

spontaneous galvanic reaction

If a reaction that is spontaneous under standard conditions is used to set up an electrochemical cell: ∆Gº will be __ 0 K will be __ 1 Eº will be __ 0

∆Gº will be < 0 K will be > 1 Eº will be > 0

If a redox reaction that is non-spontaneous under standard conditions is used to set up an electrochemical cell: ∆Gº will be __ 0 K will be __ 1 Eº will be __ 0

∆Gº will be > 0 K will be < 1 Eº will be < 0

Under standard conditions, an electrolytic cell has: ∆Gº will be __ 0 K will be __ 1 Eº will be __ 0

∆Gº will be > 0 K will be < 1 Eº will be < 0

Under standard conditions, a galvanic cell has: ∆Gº will be __ 0 K will be __ 1 Eº will be __ 0

∆Gº will be < 0 K will be > 1 Eº will be > 0

An electrochemical cell at equilibrium has: ∆Gº will be __ 0 K will be __ 1 Eº will be __ 0

∆Gº will be = 0 K will be :) 1 Eº will be = 0 The equilibrium constant doesn't change when a reaction reaches equilibrium, so at equilibrium K is still equal to whatever it was before the reaction reached equilibrium.

4Fe(s) + 3O2(g) --> 2Fe2O3(s) What is the total number of electrons gained or lost by all iron atoms in the balanced equation?

loses 3 e-/Fe atom x 4 Fe atoms = loses 12 e-

4Fe(s) + 3O2(g) --> 2Fe2O3(s) What is the total number of electrons gained or lost by all oxygen atoms in the balanced equation?

gains 2 e-/O atom x 6 O atoms = gains 12 e-

In a galvanic cell oxidation and reduction take place ___________, but at different __________

at the same time, electrodes

In a working electrochemical cell (a galvanic cell or battery), the cations in the salt bridge move toward the ________.

cathode

In an electrolytic cell, the negative terminal is the _________ and is the site of the ___________ half-reaction

cathode, reduction

The electrons flow in the external circuit...

between the electrodes specifically

If the table of standard reduction potentials is ordered with the strongest reducing agents at the top, how are the reduction potentials ordered (from top to bottom)?

from most negative to most positive

Redox reactions are often _________ compared to other reactions such as acid-base reactions or precipitation reactions.

slow

Nernst equation:

Ecell = Eºcell - (0.0591/n) log(Q)

concentration cell lower concentration = higher concentration =

oxidation reduction

Faraday constant?

96,485 C/mol = the charge of one mole of electrons

sulfide ion

S2-

1 amp =

1 coulomb/second