Popcorn Physics

[Naturalist]

Because of the pressure inside a popcorn kernel, water does not vaporize at 100C. Instead, it stays liquid until its temperature is about 175 C, at which point the kernel ruptures and the superheated water turns into steam. How much energy is needed to pop 95 grams of corn if 15 percent of a kernel's mass is water? Assume that the latent heat of vaporization for water at 175C is 0.90 times its value at 100C and that the kernels have an initial temperature of 175C.

 

The part in bold is what I don't understand.

[insane_alien]

Whats to understand? its ggiving you what you need to work it out.

 

the heat of vapourization is 0.9*(whatevever it is normally) and you don't have to consider heating the kernels up as they are already that hot.

[duckandcover]

The heat needed to reach the temperature of 175c is negated leaving only the energy needed for the chemical/physical change, due to the pressure the latent heat is only 0.9 of the original value and therefore 1 equation is all that is needed.