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.
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
Specific heat of water
Specific heat of steam
Latent Heat of vaporization of water
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Applicable Latent Heat of vaporization of water at
0.9 of2260\ kJkg^-1=2034 kJkg^-1
Water content in the given sample of pop corn kernels is
14% of95.0\ g =13.3\ g => 0.0133\ kg
Heat required to raise temperature of water content from
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
Q_2 =mL= 0.0133xx2034 = 27.05\ kJ
Total heat required
Q=Q_1+Q_2= 8.57+27.05 = 35.62\ kJ
