Chapter 13: Fundamentals of Electrochemistry

electrochemistry

a major branch of analytical chemistry that uses electrical measurements of chemical systems for analytical purposes

redox reaction

involves transfer of electrons from one species to another.

Oxidixed when it loses electrons

Reduced when it gains electrons

oxidizing agent (oxidant)

takes electrons from another substance and becomes reduced

reducing agent (reductant)

gives electrons to another substance and is oxidized in the process

TRUE OR FALSE

electric current is proportional to the rate of reeaction, and the cell voltage is proportional to the free energy change for the electrochemical reaction

electric charge (q)

measured in couloum’s (C) 

Electric current

quantity of charge flowing each second through a circuit.

• unit of current is ampere, A

• 1 ampere = flow of 1 coulomb of charge/s

electrical potential difference, E

between two points: work needed to move a standard charge between those points

• unit of potential: volts (v)

the greater the potential difference between two points, the more…

more work is required or can be done when a charged particl travels between those points

It takes work to move like charges…

toward one another

Work can be done when

opposite charges move toward one another

work required to move charger

higher energy

work done by charge moving

lower energy

Ohm’s Law

current, I, is directly proportional to the potential difference (voltage) across a circuit and inversely proportional to the resistance, R. of the circuit

Power (P)

the work done per unit time

Galvanic cell (another name: voltaic)

uses a spontaneous chemical reaction to generate electricitty

• one reagent must be oxidized and another reduced, cannot be in contact, or electrons would flow directly from the reducing agent to the oxidizing agent

• oxidizing and reducing agents are physically separated, electrons forced to flow through a wire to go from one reactant to another

• a battery is an example of galvanic cell

Reduction occurs at

Cathode

• 2e- is on the left

Oxidation occurs at

anode

• 2e- is on the right

half-reactions

written with equal numbers of electrons so that their sum includes no free electrons

potentiometer

the circuit measures the difference in electric potential (voltage) between the two metal electrodes

potentiometer has high electrical resistance

so little current flows through the meter

• ideally, no current would flow through, so we say it’s open-circuit potential 

Being negatively charged….

electrons move toward more positive electric potential

ion migration out of the bridge is greater than going inside bc

salt concentration in the bridge is much higher than found in half cells

standard reduction potential 

the reference point used to measure all other electrode potentials

• like a '“zero mark” on a ruler for measuring how easily other substnaces gain or lose electrons.

standard hydrogen electrode (SHE)

actual device or setup used to define that zero-volt reference

• where hydrogen gas bubbles over a platium metal surface in contact with an acidic solution that has hydrogen ions (H+)

Electrons flow spontaneously through the circuit from the more

negative electrode to the more positive electrode

A galvanic cell produces electricity because

the cell reaction is not at equilibrium