The water in a pressure cooker boils at a temperature greater than 100°C because
ID: 537389 • Letter: T
Question
The water in a pressure cooker boils at a temperature greater than 100°C because it is under pressure. At this higher temperature, the chemical reactions associated with the cooking of food take place at a greater rate.
(a) Some food cooks fully in 4.00 min in a pressure cooker at 120.0°C and in 32.0 minutes in an open pot at 100.0°C. Calculate the average activation energy for the reactions associated with the cooking of this food.
kJ mol-1
(b) How long will the same food take to cook in an open pot of boiling water at an altitude of 8000 feet, where the boiling point of water is 91.9 °C?
min
Explanation / Answer
a). Bu using this equation we can calculate activation energy
Ea = (RT1T2)/(T1-T2) x ln (k1/k2)
R is universal gas constant (8.314)
T1 and T2 are temperatures in K (T1 =393 K nad T2 = 373 K )
k1 and k2 are rate constants of temperatures T1 and T2 respectively
here k1 and k2 are not provided. However, rate of reaction is given and we can use it since the concentration of reactants are same
Ea =-( 8.314 x393x 373)/20 x ln (1/8) = 121.87 kJ/mole
b) Applying in the same equation
Ea = (RT1T2)/(T1-T2) x ln (k1/k2)
take the values for 100-degree Celcius
ln (k1/k2) = -(121870* 8.1 )/ (8.314 x 373 x 364.9) =- 0.87
k1/k2 = 2.38
k2 = 32/0.418 = 76 min
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