Because heat causes alcohol to volatilize, instead of burning it.
The combustion is not fulfilled since this is detached from the surface of the banknote that would be the necessary product to burn, in addition to considering that the necessary temperature is not reached
Explanation:
When water and alcohol are joined, they form a solution with high evaporation power, plus alcohol that has a higher degree of volatility than water, this is how these liquids are not retained on the surface of the banknote with heat and they are not it burns.
Heat can be transferred from one place to another by conduction in solids, convection of fluids like liquids or gases, and radiation. A temperature difference in a system causes heat to move from higher to lower temperatures
This is a single replacement reaction. So the final products are a metal and a salt with replaced cation. In this case, the final products are copper (metal) and iron sulfate (salt).
