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34 Cards in this Set
- Front
- Back
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The more positive the Eθ value what happens to the tendency to oxidise or reduce? |
The greater the tendency to gain electrons and undergo reduction |
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THe more negative the Eθ value.... |
The greater the tendency to lose electrons and undergo oxidation |
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What do Eθ values give a measure of? |
The relative ease of a reduction or oxidation process. |
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What can Eθ values be used to compare? |
oxidising or reducing power of different species |
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What happens to the strongest oxidising agents? |
They are themselves reduced. |
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What kind of Eθ values would strongest reducing agents have? |
Most negative |
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What is an electrochemical cell made of? |
two half cells which are connected together |
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What happens to the half cell with the more positive electrode potential Eθ? |
It undergoes reduction |
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What does Eθcell mean? |
Standard cell potential |
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How do you calculate the standard cell potential? |
Eθcell= EθREDuction - EθOXidation |
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True or false The standard cell potential value must always be positive |
TRUE |
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How can the feasibility of a Redox reaction be predicted? |
using standard electrode potential values. The species undergoing reduction must have the more positive Eθ value. |
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What are the limitations of predictions made using standard cell potentials? |
Kinetics Non standard concentrations of solutions |
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Why does kinetics (rate of reaction) limit the predictions made using standard cell potentials? |
(In theory a standard cell potential may predict that a reaction will occur if Eθcell =+veIn practice, the reaction may be so slow (due to high activation energy) that it is not observed. |
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How do non-standard concentrations of solutions limit predictions made using standard cell potentials? |
Using a non-standard concentration for a solution will give a value for the electrode potential that is different to the standard electrode potential. This will result in a cell potential value, which is different to that of the standard cell potential. |
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What factors affect the redox equilibria reactions taking place and result in non-standard electrode potentials? |
any non standard conditions used |
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What are standard conditions? |
temperature=298K, concentration =1.00moldm^-3 gases must be 100kPa |
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What can a standard half-cell be used for? |
To measure its standard electrode potential. |
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What are the three types of standard half cell? |
metal ion/metal half-cell metal ion/metal ion half cell non-metal/ non-metal ion half cell |
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In which half cells is a platinum electrode used? |
metal ion/metal ion half cell non-metal/non-metal ion half cell |
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Why is platinum used as an electrode? |
It is inert (will not interfere in equilibrium reaction taking place) and is an eectrical conductor (has delocalised electrons in its structure) |
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What can be used as an alternative to Pt? |
graphite (cheaper) |
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What is the solution called where the electrode is placed in? |
electrolyte solution. |
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Where does the transfer of electrons take place in a half cell? |
at the surface of the electrode. |
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What does the electrolyte in a half cell contain? |
dissolved metal ions or dissolved non metal ions |
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What are the two types of storage cells and batteries? |
primary cells (non-rechargeable) secondary cells (rechargeable) |
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What are primary cells? |
non-rechargeable and provide elctrical energy until the chemicals have reacted to such an extent that the voltage falls and the cell is flat. |
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What are secondary cells? |
(rechargeable) The chemicals react, providing electrical energy and the reaction can be reversed during the recharging process so the cell can be used again. |
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What is a fuel cell? |
A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage. |
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How are fuel cells different to storage cells? |
The fuel and oxygen flow into the cells and the products flow out (electrolyte remains in cell) So in a fuel cell electrical energy is generated continuously and they donot need to be recharged. |
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What are the two types of electrolytes a hydrogen fuel cell can have? |
alkaline or acid |
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In an alkali hydrogen fuel cell what is oxidised? |
H2 + 2OH- |
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In an alkali hydrogen fuel cell what is reduced |
1/2 O2 +H2O |
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In an acid hydrogen fuel cell what is oxidised? |
H2 |
