Explain why the following reaction occurs:
zn + 2hcl → zncl2 + h,

The reaction is spontaneous (under standard conditions) because the cell potential is positive.

Explanation:

In this reaction:

The anode is where the oxidation half-reaction takes place. In this case, the anode half-reaction is .

The cathode is where the reduction half-reaction takes place. In this case, the cathode half-reaction is .

Look up the standard reduction potential for these two half-reactions:

The standard cell potential is equal to the standard reduction potential at the cathode minus that at the anode:

.

The electrochemical reaction in the cell is spontaneous if and only if the cell potential is positive. Therefore, the reaction   is spontaneous under standard conditions.

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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