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Voltage & Current Explorer
Understanding Thermodynamics vs. Kinetics in Electrochemistry
Core Concepts
Voltage (V) is the energy difference between two points - the "push" or "pressure" that moves charge through the circuit. It measures how much energy each electron gains (or loses) moving from one electrode to the other. At 0V there's no difference, no push. Higher voltage = bigger energy difference = stronger push.
Current (i) is the flow rate - how much charge actually moves per second. Higher current means more charge flowing. This is like the flow rate of water in a pipe - how many litres per second are moving past a point.
Key Point: Electrons flow through the external circuit (the wire). In the solution, ions migrate to maintain charge balance - cations toward the cathode, anions toward the anode.
Ion Migration: When an electric field is applied, ALL ions drift simultaneously. They accumulate at electrode surfaces (shown brighter) where they form dense layers. Eventually the bulk solution depletes and you need to reset to continue.
Resistance (R) represents obstacles to charge flow - slow electron transfer kinetics, solution resistance, or mass transport limitations.
Educational Note: This simplified model focuses on the relationship between voltage (push), resistance (barrier), and current (flow). Ion accumulation is shown but the focus is on understanding Ohm's Law in electrochemical context.
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Voltage = Energy Difference
The "push" between electrodes (J/electron)
Current = Flow Rate
How much charge flows past per second (C/s)
Electrochemical Cell
Ion Accumulation: When voltage is applied, ALL ions drift in the electric field toward opposite electrodes. They accumulate at the electrode surfaces (shown brighter) and stay there. Watch the solution deplete as ions collect at electrodes!
Note: This simplified model shows ion migration and accumulation. Focus on how voltage drives ion drift, and how accumulation eventually depletes the bulk solution. Click Reset to redistribute ions and start again.
Controls
ΔG = -nFE | Higher voltage = stronger driving force
Higher resistance = slower electron transfer kinetics
Current-Voltage Relationship (Ohm's Law)
This plot shows i = E/R (Ohm's Law). The current operating point is marked with a red dot. Notice how:
- Increasing voltage (thermodynamic push) moves you up the line → more current
- Increasing resistance (kinetic barrier) makes the line shallower → less current for same voltage
- This simplified model shows the fundamental relationship, but real electrochemistry adds complexity with Butler-Volmer kinetics!
Thermodynamics (Voltage)
The cell potential (E°) and applied voltage determine the Gibbs free energy change:
ΔG = -nFE
- Positive voltage → negative ΔG → spontaneous
- Tells you the maximum work available
- Says nothing about how fast it happens!
Kinetics (Current)
The current measures the actual rate of electron transfer:
i = nFAk[species]
- Depends on activation barriers
- Limited by mass transport
- Can be slow even with favorable thermodynamics!
Teaching Points
Key Analogy: Think of voltage as the height of a waterfall (potential energy) and current as the flow rate of water (actual movement). A tall waterfall (high voltage) doesn't guarantee fast flow (high current) if there are obstacles (resistance) in the way!
In Electrochemistry: You can have a very favorable reaction (high voltage) that proceeds slowly (low current) due to high activation barriers or slow mass transport. This is why catalysts are so important - they lower the kinetic barriers without changing the thermodynamics!