Combining half cells

Question 1

WHat will happens if the voltmeter is released with a wire>

Answer 1

• electrons will flow from the area of many electrons to the area with few
• -ve electrode (negative E^ϴto the positive)

Question 2

What happens to the position of the equilibrium when the electrons flow?

Answer 2

• according to Le Chatelier’s principle…
• (most) -ve electrode
  
  • electrons lost
  • position will move to left to replace lost electrons
• (most) +ve electrode
  
  • number of electrons increases
  • equilbrium moves to the right
  • leads to reduction

Question 3

write the equation for this reaction

Answer 3

Cu²⁺(aq) + 2e^- + Zn(s) → Cu (s) + Zn²⁺(aq) + 2e^-

electrons cancel

Question 4

What is the rule of thumb for predicting the direction of electrochemical cells?

Answer 4

• most -ve E^ϴ moves to the left
• most +ve E^ϴ moves to right
• then combine using them directions

Question 5

Why is the reaction between copper and sulphuric acid not feasible?

Answer 5

• copper eqm already to right
• to react eqm would have to move to the left
  
  • opposite to what E^ϴ values are saying
• H+ would have to move to right
  
  • against what values demand

Question 6

How do you choose an oxidising agent?

Answer 6

• recap
  
  • oxd is loss of e-
  • oxd agent oxidises something by removing electrons from it, gains electrons (itself is reduced)
• to encourage reduction
  
  • eqm must be moved to left
  • must couple it to a second eqm
• in order for reduction to occur, the second eqm E^ϴ value must be greater
  
  • removes electrons from the first eqm, shifts eqm to left

Question 7

How do you choose a reducing agent?

Answer 7

• recap
  
  • reduction is gain
  • reducing agent gives electrons, itself is oxidised
• substance losing electrons is found on the right-hand side of one of these redox equilibria
• to reduce something, it must be couples with a second quilibrium with a more negative value
• substance w/ most -ve value acts as a reducing agent
  
  • electrons lost and moved into the first eqm mixture
  • Le chateliers principle
    
    • eqm moves to right