MediumChemistryHigh School (11–12)Chemical Kinetics › Temperature, the Arrhenius Equation and Collision TheoryNumericalA-Level AP IB NEET

Lentils soften by a reaction with an activation energy of 92 kJ/mol…

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Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Lentils soften by a reaction with an activation energy of $92\ \text{kJ/mol}$ . In an open pan at $373\ \text{K}$ they need $45$ minutes. In a pressure cooker the water is at $394\ \text{K}$ . By what factor is the reaction faster? How long do the lentils take in the cooker? Assume the time is inversely proportional to the rate constant.

Need a reminder? The key ideaShow

$k = Ae^{-E_a/RT}$ , with $T$ in kelvin and $R = 8.314\ \text{J/(mol K)}$ . For two temperatures, $\ln\dfrac{k_2}{k_1} = \dfrac{E_a}{R}\left(\dfrac{1}{T_1} - \dfrac{1}{T_2}\right)$ . A graph of $\ln k$ against $1/T$ is a straight line with slope $-E_a/R$ . Change $E_a$ to joules per mole before you use $R$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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