Amagnesium bar with a mass of 6.8 kg is attached to a buried iron pipe to serve as a sacrificial anode. an average current of 0.025 a flows between the bar and the pipe. what half-reaction takes place at the surface of the magnesium bar?

The half-reaction takes place at the surface of the magnesium bar is the oxidation process (losing of electrons). The chemical equation is as follow:

Explanation:

In the given situation, two reactions take place

1.  On the surface of magnesium bar:

As magnesium bar acts as anode so on the surface of magnesium bar, oxidation take place. Oxidation is a chemical reaction that result in the loss of electrons and oxidation state of magnesium increases to 2 as shown in the following equation:

2. On the surface of iron pipe:

Corrosion is a natural process which results in the deterioration or destruction of materials, in this case, it is iron.

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it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.