When baking soda is added to a penny, it undergoes a chemical reaction that causes the copper on the penny's surface to oxidize. This oxidation process results in the formation of a blue-green compound called copper carbonate hydroxide (Cu2(OH)2CO3).

- Chemical Reaction:

Penny (Copper) + Sodium Bicarbonate (Baking Soda) + Oxygen --> Blue-Green Compound (Copper Carbonate Hydroxide)

4 Cu(s) + NaHCO3(aq) + O2(g) --> Cu2(OH)2CO3(s) + Na2CO3(aq)

Factors Influencing the Reaction:

1. Baking Soda Concentration: The concentration of baking soda in the solution affects the rate and extent of the reaction. A higher concentration of baking soda leads to a faster reaction, resulting in a more pronounced blue-green color on the penny.

2. Temperature: Increasing the temperature accelerates the reaction. Applying heat can intensify the blue coloration, making the effect more noticeable.

3. Time: The longer the penny is exposed to the baking soda solution, the more complete the copper oxidation reaction will be, resulting in a deeper and more prominent blue-green color.

It's worth mentioning that the blue-green color obtained from this reaction is not permanent and will fade over time due to exposure to air and environmental conditions.