How does a salt bridge prevent charge buildup in a galvanic cell?

[gkangelexa]

As electrons leave one half of a galvanic cell and flow to the other, a difference in charge is established. If no salt bridge were used, this charge difference would prevent further flow of electrons.

Why would the charge difference prevent further flow of electrons ??

 

[Modulated]

Because you'd be taking electrons away from the side that's already positively charged, and adding them to the side that's already negatively charged. By Coulomb's Law both of these are energetically unfavourable (i.e., to do them you have to do work against a force pushing the opposite way).