Electrode potentials Flashcards
Definition of a standard electrode potential
The e.m.f of a half cell compared with a standard hydrogen half-cell. Measured at standard conditions: 298K 1 atm/ 100kPa 1 mol dm-3 solutions.
What are the limitations of doing predictions using E values.
E values predict the feasibility of a reaction but not necessarily the rate.
The E values are given at standard conditions. The concentration can differ in actual reactions.
The gives different voltage values.
Fuel cell
A cell that uses energy from the reaction of fuel with oxygen to create a voltage.
How do non-chargeable cells differ from chargeable ones.
Non rechargeable only provide energy until all the chemicals have reacted.
Whereas, in rechargeable cells the reaction can be reversed to regenerate the original chemicals. The restart the redox reactions.
Fuel cell vehicles
Use hydrogen gas as a fuel, in a fuel cell.
Hydrogen rich substances can also be used, like alcohols:
They are mixed with water to produce Hydrogen gas and Carbon dioxide as a waste product.
Liquid fuels are easier to store than gas, which is why alcohols are prefered.
Advantages of fuel cell vehicles
Less pollution is produced: less carbon dioxide and carbon monoxide. is produced compared to burning hydrocarbons.
More efficient: Hydrogen FCVs are more efficient than petrol engines
How is hydrogen fuel stored in vehicles (3).
Liquid: H2 is placed under high pressure.
This required very low temperature and thermos flask which are expensive and spacious.
Adsorption: H2 can be adsorbed onto the surface of a solid material.
Absorption: H2 can be absorbed into some solid materials.
Limitations of hydrogen fuel cells.
Expensive and problematic to store and transport.
It is not always possible to store hydrogen as liquid.
Adsorbers and absorbers have a limited lifetime.
Fuel cells used toxic chemicals when in production.
Fuel cells have limited lifetime.
