give the 2 consistent qualities of redox equilibria half equations
always reversible
electrons always written on left
what does increased reactivity mean for equilibrium position
more reactive means equilibrium further left
eg) Na+(aq) + e- —> Na(s)
Na is more easily donates electron (as relatively more reactive)
causing eqn to shift left
give reactivity series
what is an electrode
physical representation of a redox equilibrium
draw an electrode for Mg2+(aq) + 2e- –> Mg(s)
explain how electrons more in an electrode of the equation Mg2+(aq) + 2e- –> Mg(s)
forwards: Mg2+ bumps into solid, gains 2e- and turns into mg atoms
backwards: Mg atoms dumping 2e- on solid + floating off as Mg+ ions
why is it possible that Mg can be a solid on its own in the electrode
Mg can conduct
what if the solid in equilibrium isn’t a conductor
use a separate platinum electrode
inert conductor
(it being inert means it won’t interfere with equilibreum
draw equilibrium if there is a gas (for H+)
define potential
measure of how positive something is
what potential does an element have if equilibrium is further left
equilibrium further left
[e-] higher
conductor more negative
lower potential
what is potential measured in
volts
what is potential if equilibrium is further right
equilibrium further right
[e-] conc lower
conductors is less negative
higher potential
what is potential of electrode described as meaning something is “more positive” not “positive”
potential of an electrode is a relative measure of the equilibrium position
you can never know for sure as equilibrium can be anywhere
how to measure the potential of an electrode
imposible to measure potential of individual electrode
measure them relative to standard hydrogen electrode
what are you measuring relative to standard hydrogen electrode
potential difference
what does non-standard conditions of electrode mean
think of what direction equilibrium would shift
e.g higher pressure shift equilibrium to side with less moles
what is the best oxidising and reducing agent elements/substances
best oxidising: H2O2 / H+
best reducing: Na
why do you not draw salt bridges as dashed line
circuit wouldn’t be complete
how to choose the best oxidising agent
takes electrons most easily
forwards reaction is easy
equilibrium further to right
highest electrode potential
what does an electrochemical cell consist of
two electrodes, connected via a high resistance voltmeter and a salt bridge
describe a salt bridge
filter paper soaked in KNO3(aq)
conducts electricity
why is KNO3(aq) a good solution for salt bridge
K+ and NO3- compounds are all soluble
(and never affects ions in reaction)
what does high resistant voltmeter mean
barrier that stops electrons moving around
