Electrochemistry Flashcards
What is electrochemistry?
Deals with the interconversion of electrical energy and chemical energy, electrical effects occur as a result of the movement of electronically charge either as ions in solution or electrons in a conductor
Electric current?
The rate at which charge passes a point
When does an electric current flow?
If there is a potential difference between two points in a circuit, the potential difference represents the driving force that pushes the electrons or ions around the circuit
Ohms law?
V = I x R
potential difference = current x resistance
Resistance in a cicutty?
For a constant potential difference the lower the resistance in a circuit the higher the current
Emf?
If an electrochemical cell is used to produce a high current the voltage falls as the reactants are used up, however if the resistance of the current is his the current is low and the voltage does not fall so quickly, when the resistance is extremely high an infinitesimal small current flows and the voltage is at its maximum, the maximum voltage is called the zero current cell potential also known as the electromotive force and given the symbol Ecell
Reductions?
When electrons are gained
Oxidations?
When electrons are lost
Electrolyte?
Substance that when dissolved gives a solution that conducts electricity, most are ionic substances, in an electrolyte solution the charge is carried between the electrodes by dissolved ions
Conductivity cell?
The properties of electrolyte solution can be studied in a conductivity cell, consist of two platinum electrodes held apart at a fixed distance in a solution, platinum is used since it is inert and very reactive, a voltage is applied between the electrodes and the resistance R is measured the resistance is a measure of how difficult the motion of ions is between the electrodes, to prevent any chemical reactions due to electrolysis it is usual to make conductivity measurements with an alternating current
What does conductivity depend on?
The number of ions in solution, a solution with a higher concentration of ions has a higher conductivity
Strong electrolytes?
KCl or Na2SO4 are fully ionised in solution and so are strong electrolytes
Limiting molar conductivity?
For a strong electrolyte measurement using a conductivity cells shows that the molar conductivity decreases as the solution becomes more dilute, the interactions between ions in a solution affect the movement of ions through solution, these interactions are less important in dilute solution so molar conductivity increases with dilution, eventually the molar conductance ceases to increase with dilution and approaches a limiting value called the limiting molar conductivity
What happens when the solution is very dilute?
The ions are far enough apart that they do no interact with each other and so behave independently of one another, each ion makes its own independent contribution to the molar conductivity
Ionic conductivity values?
Known as limiting values since they are only valid in very dilute solutions at infinite dilution, most singly charged anions or cations have similar values of ionic conductivity values since each ion carries the same amount of charge, divalent ions carry more charge so they have higher values