Question

In order for a combustible substance to ignite, it must first attain a certain temperature called the 'autoignition point,' which is the minimum temperature that the substance requires to begin combustion. In this case, the banknote didn't 'burn' because the water present absorbs the majority of the energy given off by the combustion of ethanol, which keeps the temperature of the banknote below its ignition point. As per the explanation given by the video, "water protects the paper by absorbing the energy of alcohol combustion." Water is particularly good at absorbing energy with a minimum increase in temperature due to its hydrogen bonding, which is the attractive forces between the polar ends of water molecules.

True
False

Answer 1

The statement is true; water's high heat of vaporization and hydrogen bonding allow it to absorb the energy from ethanol's combustion, helping to keep the temperature of the paper below its ignition point.

Step-by-step explanation:

The autoignition point of a substance is the minimum temperature required to initiate combustion without the presence of an external flame or spark. Water, with its high heat of vaporization and ability to form hydrogen bonds, absorbs a substantial amount of energy with minimal temperature increase. This characteristic allows water to act as an effective heat sink, preventing a material like paper from reaching its autoignition point. When water is present, it safeguards the paper by absorbing the energy from the ethanol's combustion and therefore keeps the temperature of the paper below its ignition point. The evaporation of water also takes away heat from the surroundings, ensuring the paper's temperature remains low. Hence, the statement that 'water protects the paper by absorbing the energy of alcohol combustion' is true based on water's properties.