Is lemon juice and pennies chemical change?

Yes, the reaction between lemon juice and pennies is a chemical change.

When lemon juice (citric acid) comes into contact with a copper penny, a chemical reaction takes place. The citric acid in the lemon juice reacts with the copper on the penny to form copper citrate, which is a new substance with different properties than either the citric acid or the copper. This reaction is evidenced by the formation of a green substance on the surface of the penny.

The chemical equation for this reaction is:

Cu(s) + 2H3C6H5O7(aq) → Cu(C6H5O7)2(aq) + H2(g)

In this equation, Cu represents copper, H3C6H5O7 represents citric acid, Cu(C6H5O7)2 represents copper citrate, and H2 represents hydrogen gas.