To produce 350 cal of heat, how many grams of isopropyl alcohol must boil? The heat of fusion of isopropyl alcohol is 21.4 cal/g and the heat of...

First of all, boiling the alcohol (or other materials, such as water, among others) needs energy and does not generate heat. This is the reason, when water or rubbing alcohol (isopropyl alcohol) evaporates, we get a cooling sensation (since some heat from our body has been utilized for its evaporation). Secondly, a number of parameters are missing. The initial state (solid or liquid) and the temperature must be provided. We also need the specific heat in solid and liquid phases and melting and boiling points of the alcohol.

Let us say the alcohol is initially in the solid state at a temperature Ti. Let us say Tm and Tb are melting and boiling points and Ss and Sl are specific heat values in solid and liquid phases. Then energy would be required to

• increase the temperature from initial value to melting point


• phase change from solid to liquid (heat of fusion)


• increase in temperature from melting point to boiling point


• phase change from liquid to gas (heat of vaporization)

This way, we can calculate the heat required.

For the given case and given information, we can assume the alcohol to be in liquid phase at the boiling point. 350 cal of heat would be able to boil

350 cal / (159 cal/g) = 2.2 g isopropyl alcohol.

Thus, we can boil 2.2 g of alcohol with 350 cal heat, without any temperature increase.

To generate heat, the alcohol will need to undergo combustion.

Hope this helps.