How much energy is needed to pop a kernel of popcorn?

Because of the pressure inside a popcorn kernel, water does not vaporize at 100.0°C. Instead, it stays liquid until its temperature is about 175.0°C, at which point the kernel ruptures and the superheated water turns into steam. How much energy is needed to pop 95.0 g of corn if 14% of a kernel’s mass consists of water? The latent heat of vaporization for water at 175.0°C is 0.90 times its value at 100.0°C and the initial temperature is 21.0°C.

1 Answer
A08
Apr 7, 2018

Specific heat of water #=4.186\ kJkg^-1C^-1#
Specific heat of steam #=2.108\ kJkg^-1K^-1#
Latent Heat of vaporization of water #=2260\ kJkg^-1#
.-.-.-.-.-.-.-.-.-.-.-

Applicable Latent Heat of vaporization of water at #175^@C# is

#0.9# of #2260\ kJkg^-1=2034 kJkg^-1#

Water content in the given sample of pop corn kernels is

#14%# of #95.0\ g =13.3\ g => 0.0133\ kg#

Heat required to raise temperature of water content from #21.0# to #175.0^@C#

#Q_1 =msDeltat#
#Q_1= 0.0133 xx4.186 xx (175.0-21.0) = 8.57\ kJ#

Heat required for change of state of water content at #175^@C#

#Q_2 =mL= 0.0133xx2034 = 27.05\ kJ#

Total heat required

#Q=Q_1+Q_2= 8.57+27.05 = 35.62\ kJ#

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