Lesson 11 Electrochemistry Flashcards
17.1 - 17.3
Redox Reactions
Chemical reaction that involves a transfer of electrons between two species.
Electrochemistry (Definition)
The study of electricity and how it relates to chemical reactions.
Electricity (Definition)
The flow of electrons.
Oxidation Numbers (States)
Shows the total number of electrons which have been removed from an element (positive oxidation state/number) or added to an element (negative oxidation state/number) to get to its present state.
Oxidation Numbers Rules (Group 1A & 2A metals)
1A = +1
2A = +2
Oxidation Numbers Rules (Element by itself)
Zero
Cl2 = 0
Ba = 0
Mg = 0
Oxidation Numbers Rules (Halogens)
Usually -1, positive with Oxygen
Oxidation Numbers Rules (H)
+1 w/ nonmetals
-1 w/ metals
Oxidation Numbers Rules (Oxygen)
Usually -2
-1 w/ peroxides (H2O2)
Oxidation Numbers Rules (F)
Always -1
OIL RIG
Oxidation is LOSS (of electrons)
Reduction is GAIN (of electrons)
Oxidizing Agent
Reactant that is being reduced (gaining electrons).
-species that causes the oxidation.
Reducing Agent
Reactant that is being oxidized (loses electrons).
-species that causes reduction.
Oxidized (Does Oxidation Number go up or down)
Up (loss of electrons)
Reduced (Does Oxidation Number go up or down)
Down (gain of electrons)
Steps for Balancing Redox Reactions in Acidic Solutions
- Determine the Oxidation Numbers
- Figure out what’s been oxidized and
reduced. - Write the half equations.
- Balance atoms other than the O and H
- Add H2O to balance O, and H+ to balance
H. - Add electrons to balance charges
- Multiply half reactions to make the number
of electrons equal on both sides. - Add half reactions together and cancel out
stuff that appears on both sides. - Do a final check to make sure everything
balances.
Steps for Balancing Redox Reactions in Basic Solutions
- Determine the Oxidation Numbers
- Figure out what’s been oxidized and
reduced. - Write the half equations.
- Balance atoms other than the O and H
- Add H2O to balance O, and H+ to balance
H. - Add electrons to balance charges
- Multiply half reactions to make the number
of electrons equal on both sides. - Add half reactions together and cancel out
stuff that appears on both sides. - For each H+ add one OH to both sides.
- Combine H+ and OH- to make H2O.
- Subtract H2O from both sides if possible.
- Do a final check to make sure everything
balances.
Galvanic (Voltaic) Cell
Electrochemical cells in which spontaneous redox reactions produce electrical energy.
Anode
Cell in which oxidation takes place. (Loses mass)
Cathode
Cell in which reduction takes place. (Gains mass)
Salt Bridge
Keeps the solutions nuetral.
Salt Bridge (Where do anions flow)
Anions flow into the anode (positive ions break apart from solid metal when they lose electrons to make the solution more positive).
Salt Bridge (Where do cations flow)
Cathode (positive ions in solution gain electrons (reduction) to form neutral metals and combine with cathode to leave a more negative solution).
Electrode that loses mass
Anode
Oxidation occurs at the anode.
Electrode that gains mass
Cathode
Reduction occurs at the cathode.
Electrochemical Cell (Galvanic)
Device used to generate electrical energy from a spontaneous oxidation-reduction reaction.
Red Cat and An Ox
Reduction is cathode.
Anode is Oxidation.
Cell Notation
Shorthand notation of galvanic (voltaic) (spontaneous) cells.
Cell Notation Rules
Double vertical line (||) used to separate anode and cathode. (Anode on the right).
Single vertical line (|) used to separate different states of matter on the same side.
Commas (,) used to separate like states of matter on the same side.
(Don’t show ions that don’t change charges)
Cell Potential from E (Standard Conditions) Equation
Ecell = E(reduction/cathode) - E(oxidation/anode)
Negative or Smaller Ecell Value is always the (Anode or Cathode)?
anode
How to identify and Oxidation-Reduction Reaction?
The oxidation numbers must have changed.
