REDOX REACTIONS PT.2

Pg 148-

What is the function of the SHE

• Used to show where a ,substance is on the SHE table, in relation to hydrogen which has an electrode potential of 0

Why is the standard hydrogen electrode chosen

• Electrode potential of 0V

• Reading on the voltmeter of the external circuit will be equal to the other half-cell’s electrode potential

What is used if the half cell does not contain a metal and why is it chosen

• Platinum is used as the electrode

• Unreactive (inert) precious metal

• Not be oxidized=weak reducing agent

Hydrogen electrode is always connected as the

Anode

Where is Pt written in cell notation and how does it act like a catalyser

On the outside of the cell

By increasing the surface contact area

If electrode potential is positive it is being reduced at the ____ and if negative being oxidized

cathode

when is the other substance acting as the anode

IF the standard electrode potential is negative (meaning it’s being oxidized) and pt is acting as the cathode( H ions reduced to H gas)

What does cell potential tell us and how is it calculated

Tells us if reaction is spontaneous or not

• Electrode potential of CATHODE - Electrode potential of ANODE

POSTIVE ANSWER MEANS SPONTANEOUS

Do reactions between weak OAs and Weak RAs react spontaneously

NO only between strong OAs and strong RAs

Just a little note

When the ____+2e- (for example) is ont the left what is happening and when its on the right what is happening

Left= Gaining

Right= Losing

With suitbale electrolytes always try between

Sulphate and a nitrate

When circuit is complete and current flows what will happend with the concentration in regards with

Fe(s) + Ag(aq) - Fe(aq) +Ag(s)

Fe(aq) concentration will increase consistently as it becomes less of a solid

Ag(aq) concentration will decrease as it becomes more solid

What is current affected by and what is the relationship between the two

Number of electrons moving per unit time

More electrons the more the current increases

If ions flow through electrolytes easier what happens to current and vice versa

It increases

Current and

Potential difference and

Reaction rate

Equilibrium

What happens when you increase concentration of all electrolytes and the salt bridge

• Ions flow easier

• Decreases internal resistance

• Rate of flow of ions increase= current increasing

Current flows from.

Electrons flow from

Positive to negative

Negative to positive

When the concentration of electrolyte decreases what also decreases

The reaction rate

Electrons flow from - to +

The concentration by the cathode becomes less as the electrode increase in mass(becomes more solid)

Reaction rate of Fr decreases

How does SA affect reaction rate

• Increase SA of electrodes

• More effective collisions per unit time

• More electrons flow over unit time and current increases

• Lessens internal resistance of the cell

How to lessen internal resistance of the cell(4)

• Higher electrolyte concentration to ensure easy flow of ions;rate of flow of ions increases = current increases

• Shorten length fi salt bridge,decreasing the time it takes for ions to flow

• Widen the salt bridge allowing more ions to flow per unit time

• Use electrodes with greater SA

When cell reaches dynamic equilibrium what happens to emf

The cell potential becomes 0V

Any factors that favour the FORWARD REACTION will cause the cell potential to

Increase

3 ways to make sure forward reaction is favoured and the cell potential to increase

• Concentration by cathode should be increased by adding more _NO3

• Initial concentration by anode should be lower than standard concentration

• Operate cell temperature lower than 25C,this will favor the exothermic reaction

What are two flops with decreasing the cell temp.

• Current will decrease as there are less effective collisions per unit time slow down flow of ions between electrolytes

whats a spectator ion

remians unchanged after reaction and oesnt participate. The oxidation number stays the same

Cations (positive ions) typically flow from the anode to the cathode within the cell, while anions (negative ions) flow in the opposite direction. 

Explanation: