electrochemistry

Question 1

what reaction is used to create a current in electrochemical cells

Answer 1

redox reactions

Question 2

when does a metal produce a voltage in an electrochemical cell

Answer 2

when a metal is dipped into a solution of its ions and is connected to another half cell

Question 3

how are electrons left behind on the metal strip

Answer 3

when metal atoms give up electrons and dissolve to form metal ions

Zn(s) → Zn2+(aq) + 2e-

Question 4

what may happen if the electrons remain on the surface

Answer 4

some of the metal ions may reform with the electrons to make their atoms

Zn2+(aq) +2e- →Zn(s)

Question 5

what increases the likelihood of atoms reforming in electrochemical cells

Answer 5

when there is an excess of electrons on the metal strip

Question 6

what creates a larger potential difference in an electrochemical cell

Answer 6

the greater tendency of metal atoms to produce ions as some atoms dissolve in solution faster than others

Question 7

what half cell would be the positive electrode

Answer 7

the half cell with the smaller build up of electrons on its surface of the metal strip

Question 8

what does emf measure and its equation

Answer 8

• the force that moves the electrons around the circuit
• E(cell) = E°(reductio) - E°(oxidation) or E°(cell) = E°(right) - E°(left)

Question 9

what increases emf

Answer 9

the greater difference in electrode potential

Question 10

what way do electrons flow in an electrochemical cell

Answer 10

from the half cell with the higher electron build up to the half cell with the lower electron build up

Question 11

what is the salt bridge used for

Answer 11

its used as a conductor so that the ions are free to move on the bridge and it keeps the cells electrically neutral

Question 12

what does a salt bridge usually contain

Answer 12

solution of potassium chloride or potassium nitride

Question 13

what causes the equilibrium to shift in a electrochemical cell

Answer 13

The movement of electrons from one half cell to another

Question 14

what happens when the concertation of electrons increases in one of the half cells

concerntration of electrons increases in half cell B

Answer 14

• the ions in cell B will bond with the new delocalised electrons to form its atoms
• this moves the equlibrium to the left in half cell A
• in half cell A this will cause more ions to be formed which would preodcue more elctrons in cell A

Question 15

why does hydrogens electrode potential 0

Answer 15

its 0 by definition as its what we compare everything else to

Question 16

state the meaning of the term elecrochemical series

Answer 16

metals are ordered by their electrode power in comparison to a H2/2H+ half cell

Question 17

whats the standard conditions for an electrochemical cell

Answer 17

1 mol dm-3
298K
100kPa (only affects half cells with gasses)

Question 18

why does a half cell have to be connected to another half cell to measure potential (E)

Answer 18

the potential (E) of a half cell cant be measureed directly

Question 19

define the term standard electrode potential

Answer 19

• E.m.f/ voltage/ potnetial difference of an electrochemical cell
• comprised of X(s)/X2+(aq) half cell with S.H.E
• 298K, 100kPa, 1 mol dm-3

Question 20

what does a more postitve E°/V value tell us

Answer 20

increasing oxidising power

Question 21

what does a more negative E°/V value tell us

Answer 21

increasing reducing power