Células, razões redox e limites de previsão
Introduzido| English | Significado |
|---|---|
| standard electrode potential/ˈstændəd ɪˈlektrəʊd pəˈtenʃl/ | potencial padrão do eletrodo |
| potential/pəˈtenʃl/ | potencial |
| feasibility/ˌfiːzɪˈbɪlɪti/ | viabilidade |
| activation barrier | barreira de ativação |
Which way do electrons move?
- In a spontaneous zinc–copper cell, zinc loses electrons and copper(II) ions gain them. The negative electrode is zinc.
- Electrons move through the external wire. Salt-bridge ions carry charge inside the connecting bridge; electrons do not flow through the solutions.
A ponte salina transporta carga através do movimento _____.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Íons se movem pela ponte. Elétrons se movem pelo condutor externo.
Compare standard reductions
- A standard electrode potential 标准电极电势 is measured relative to the standard hydrogen electrode at 298 K, 100 kPa gas pressure and 1.00 mol per cubic decimetre solutions.
- With reduction potentials +0.80 and +0.34 V, the more positive couple is reduced. Cell voltage is 0.80 − 0.34 = +0.46 V.
Qual par é reduzido em uma célula espontânea com potenciais de redução de +0.54 V e −0.25 V?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
O potencial de redução mais positivo corresponde à redução no eletrodo positivo.
Encontre a tensão padrão da célula a partir dos potenciais de redução de +0.54 V e −0.25 V.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
0.54 − (−0.25) = 0.79 V.
Balance electrons without scaling voltage
- Copper oxidation gives two electrons; each silver ion needs one. The net equation is Cu + 2Ag⁺ → Cu²⁺ + 2Ag.
- Multiplying a half-equation changes amount and total transferred charge together. It does not multiply the voltage.
Electrons move in the wire, while ions carry current in the salt bridge.
Duplicar uma semi-reação de redução duplica seu potencial eletrodico padrão.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
O potencial é por unidade de carga; escalar a quantidade não o altera.
Use the actual redox ratio
- Acidified manganate(VII) gains five electrons per MnO₄⁻, so its ratio with one-electron Fe²⁺ is 1:5.
- 22.40 cubic centimetres of 0.0200 moles per cubic decimetre titrant is 0.000448 mol. It reacts with 0.00224 mol Fe²⁺.
State the prediction limits
- Positive standard voltage predicts thermodynamic feasibility 可行性 under standard conditions. It does not prove an observable reaction rate.
- A high activation barrier 活化能垒 can make reaction slow. Non-standard concentrations can change the potential 电势 and the predicted direction.
At standard conditions, a positive cell voltage is compatible with a very slow reaction.
Balance electron transfer before using a titration ratio. Compare standard electrode potentials for a standard prediction, then state concentration and rate limits.
Quais duas condições limitam uma previsão baseada apenas nos potenciais padrão?
Difficulty 2/5 · 140 coins + a small bonus on first completion today
Barreiras de velocidade e alterações de concentração limitam o que o cálculo termodinâmico padrão prevê.