Zn(NO3)2 Cu(NO3)2

Zn anode

Zn2+ Cu2+

Cu cathode

A voltmeter (potentiometer) measures __________ through _______________ in an electrochemical cell.

A. Current due to electrons

moving, solutions

B. Current due to ions moving,

solutions

C. Current due to electrons

moving, a conducting wire

D. Current due to ions moving, a

conducting wire

𝐕𝐨𝐥𝐭𝐚𝐠𝐞 ∝ 𝐞−𝐜𝐮𝐫𝐫𝐞𝐧𝐭 𝐭𝐡𝐫𝐨𝐮𝐠𝐡 𝐰𝐢𝐫𝐞

𝑍𝑛 𝑠 𝑍𝑛2+ 𝑎𝑞, 1𝑀 𝐶𝑢2+ 𝑎𝑞, 1𝑀 𝐶𝑢(𝑠)

https://phet.colorado.edu/en/simulation/sugar-and-salt-solutions

NaCl

Which solution would you want in order to produce light from the lightbulb?

A. 1 M Sucrose solution

B. 1 M NaCl

C. 2 M NaCl

Which aqueous solution could produce the greatest voltage (brightest lightbulb/most energy)?

A. Coffee with a lot of sugar (1 M)

B. Pure water (pH=7)

C. Gatorade ([KPO42-]=0.0004 M)

D. 1 M solution K3PO4

Conductivity ∝ ion current through solution ∝ voltage

https://www.youtube.com/watch?v=P5QlfMRvvF8

2𝐴𝑔𝑁𝑂3 𝑎𝑞 + 𝐶𝑢 𝑠 → 2𝐴𝑔 𝑠 + 𝐶𝑢2+ 𝑎𝑞 + 2𝑁𝑂3−(𝑎𝑞)

What will be the measured voltage the instant that the copper wire is added to the 1 M solution AgNO3 at 25 ℃?

What does the º symbol mean?

Standard state

25 ºC

1 M concentrations

1 bar pressure (for gases)

𝜺° = 𝟎. 𝟒𝟔𝟑 𝑽We are NOT at standard conditions!

At time t=t1, the instant the reaction starts

𝑨𝒈+ ≈ 𝟏𝑴

𝑪𝒖𝟐+ ≪ 𝟏𝑴

𝜺 = 𝜺° −𝑹𝑻

𝒏𝑭𝒍𝒏𝑸

𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq

𝐐

𝐥𝐧(𝐐)

𝐐 → 𝟎𝐥𝐧 𝐐 → −∞

𝐐 → 𝟏𝐥𝐧 𝐐 → 𝟎

𝜺° = 𝟎. 𝟒𝟔𝟑 𝑽We are NOT at standard conditions!At time t=t1, the instant the reaction starts

𝑨𝒈+ ≈ 𝟏𝑴

𝑪𝒖𝟐+ ≪ 𝟏𝑴

𝜺 = 𝜺° −𝑹𝑻

𝒏𝑭𝒍𝒏𝑸

𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐

𝜺 > 𝟎. 𝟒𝟔𝟑 𝐕 𝐚𝐭 𝐭 = 𝐭𝟏

large negativenumber

What will be the measured voltage the instant that the copper wire is added to the 1 M solution AgNO3 at 25 ℃?

What does the º symbol mean?

Standard state

25 ºC

1 M concentrations

1 bar pressure (for gases)

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq

What will happen over time?

• 𝑨𝒈+ ≈ 𝟏𝑴

• 𝑪𝒖𝟐+ ≪ 𝟏𝑴

• 𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 ≪ 𝟏

• Spontaneous reaction, ΔG(t1) < 0

• Potential difference, ε(t1) > 0.463 V

• Equilibrium constant, K?

𝜺° =𝑹𝑻

𝒏𝑭𝒍𝒏𝑲 → 𝑲 = 𝒆𝒏𝑭𝜺°/𝑹𝑻

(initial)𝒕 = 𝒕𝟏 𝒕𝟐 > 𝒕𝟏

Predict the magnitude of K.

A. Less than 1

B. Equal to 1

C. Greater than 1

D. Much much greater than 1

𝜺° =𝑹𝑻

𝒏𝑭𝒍𝒏𝑲 → 𝑲 = 𝒆𝒏𝑭𝜺°/𝑹𝑻

• 𝑨𝒈+ ≈ 𝟏𝑴

• 𝑪𝒖𝟐+ ≪ 𝟏𝑴

• 𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 ≪ 𝟏

•Spontaneous reaction, ΔG(t1) < 0

•Potential difference, ε(t1) > 0.463 V

•Equilibrium constant,

𝑲 = 𝟒. 𝟒𝟒𝒙𝟏𝟎𝟏𝟓

(initial)

What will happen over time?

𝒕 = 𝒕𝟏 𝒕𝟐 > 𝒕𝟏

Q and K are measures of the extent of a chemical reaction

Q = KQ

∞0

∆𝐺 = ∆𝐺° + 𝑅𝑇𝑙𝑛𝑄

∆𝑮° is the energy released when a reaction spontaneously proceeds from the standard state to equilibrium

∆𝐺° = −𝑅𝑇𝑙𝑛𝐾

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq K = 4.44x1015

Q=1

Q < K Q > K

(Final) (Initial)

0∆𝐺° = −𝑅𝑇𝑙𝑛𝐾 − (−𝑅𝑇𝑙𝑛 1 )

Equilibrium(Final)

Standard state(Initial)

What does the º symbol mean?

Standard state

25 ºC

1 M concentrations

1 bar pressure (for gases)

Q and K are measures of the extent of a chemical reaction

𝜀 = 𝜀° −𝑅𝑇

𝑛𝐹𝑙𝑛𝑄

𝜺° is the potential difference arising from the differences in electrostatic interactions at the standard state relative to the interactions at equilibrium𝜀° =

𝑅𝑇

𝑛𝐹𝑙𝑛𝐾

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq K = 4.44x1015

(Final) (Initial)

0𝜀° =

𝑅𝑇

𝑛𝐹𝑙𝑛𝐾 − (

𝑅𝑇

𝑛𝐹𝑙𝑛 1 )

Q = KQ

∞0 Q=1

Q < K Q > K

Equilibrium(Final)

Standard state(Initial)

• 𝑨𝒈+ ≈ 𝟏𝑴

• 𝑪𝒖𝟐+ ≪ 𝟏𝑴

• 𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 ≪ 𝟏

•Spontaneous reaction, ΔG(t1) < 0

•Potential difference, ε(t1) > 0.463 V

•Equilibrium constant,

𝑲 = 𝟒. 𝟒𝟒𝒙𝟏𝟎𝟏𝟓

(initial)

What will happen over time?

𝒕 = 𝒕𝟏 𝒕𝟐 > 𝒕𝟏

We are NOT at standard conditions!

Q and K are measures of the extent of a chemical reaction

−𝑅𝑇𝑙𝑛𝐾 + 𝑅𝑇𝑙𝑛𝑄

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq

∆𝐺 =

−𝑅𝑇𝑙𝑛𝐾 − (−𝑅𝑇𝑙𝑛 1 )

−𝑅𝑇𝑙𝑛(1) − (−𝑅𝑇𝑙𝑛𝑄)0

Initial (t = t1)

K = 4.44x1015

Q = KQ

∞0 Q=1

Q < K Q > K

EquilibriumStandard state

𝜀 = 𝜀° −𝑅𝑇

𝑛𝐹𝑙𝑛𝑄

0

∆𝐺°

• 𝑨𝒈+ ≈ 𝟏𝑴

• 𝑪𝒖𝟐+ ≈ 𝟎𝑴

• 𝑸 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 ≪ 𝟏

•Spontaneous reaction, ΔG(t1) < 0

•Potential difference, ε(t1) > 0.463 V

•Equilibrium constant,

𝑲 = 𝟒. 𝟒𝟒𝒙𝟏𝟎𝟏𝟓

(before equilibrium)

• Less 𝑨𝒈+

• More 𝑪𝒖𝟐+

• Larger 𝑸

• ΔG(t2) > ΔG(t1), but still negative (spontaneous)

• Smaller potential difference, but ε > 0 V

• Same K

(initial)𝒕 = 𝒕𝟏 𝒕𝟐 > 𝒕𝟏

What will happen over time?

Q and K are measures of the extent of a chemical reaction

QQ = K

Q < K Q > K ∞0

Equilibrium

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq

Initial (t = t1)

K = 4.44x1015

t = t2

• Even less 𝑨𝒈+

• Even more 𝑪𝒖𝟐+

• Larger Q, 𝐐 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 → 𝑲

•𝚫𝑮 𝒕𝟑 → 𝟎 > 𝚫𝑮 𝒕𝟐 > 𝚫𝑮 𝒕𝟏 , but still negative (spontaneous)

• 𝜺(𝒕𝟑) → 𝟎 < 𝜺(𝒕𝟐) < 𝜺(𝒕𝟏), but still positive

• Same K

(at equilibrium)(near equilibrium)𝒕 = 𝒕𝟑 𝒕 = 𝒕𝟒

What will happen over time?

Q and K are measures of the extent of a chemical reaction

QQ = K

Q < K Q > K ∞0

Equilibrium

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq

Initial (t = t1)

K = 4.44x1015

t = t2t = t3

• Even less 𝑨𝒈+

• Even more 𝑪𝒖𝟐+

• Larger Q, 𝐐 =𝑪𝒖𝟐+

𝑨𝒈+ 𝟐 ≫ 𝟏

• 𝚫𝑮 𝒕𝟑 → 𝟎 > 𝚫𝑮 𝒕𝟐 > 𝚫𝑮 𝒕𝟏 ,

but still negative (spontaneous)

• 𝜺(𝒕𝟑) → 𝟎 < 𝜺(𝒕𝟐) < 𝜺(𝒕𝟏), but still positive

•Same K

(at equilibrium)

• Even less 𝑨𝒈+

• Even more 𝑪𝒖𝟐+

• 𝑸 = 𝑲

• 𝚫𝑮 = 𝟎 J/mol

• 𝜺 = 𝟎 𝑽

• Same K

(near equilibrium)𝒕 = 𝒕𝟑 𝒕 = 𝒕𝟒

What will happen over time?

Q and K are measures of the extent of a chemical reaction

2Ag+ aq + Cu s → 2Ag s + Cu2+ aq K = 4.44x1015

QQ = K

Q < K Q > K ∞0

t = t4

(equilibrium)∆𝑮 = 𝟎, 𝜺 = 𝟎

Initial (t = t1)

t = t2t = t3

2Ag+ aq + Cu s ⇌ 2Ag s + Cu2+ aq

The reaction does NOT stop!