The unit of rate constant for third order reaction is:
Correct answer: C. mol-2 dm6 s-1
- A. s-1
- B. mol-1 dm3 s-1
- C. mol-2 dm6 s-1
- D. mol dm-3 s-1
Explanation
In a third-order reaction, the rate law typically involves three concentration terms, such as [A]2[B], leading to a rate constant with units of mol-2 dm6 s-1. This arises because the concentration terms must cancel out the units of concentration raised to the power of three (from the three reactants) to leave the rate with units of concentration/time. Other options are incorrect because they correspond to different reaction orders: first-order (s-1), second-order (mol-1 dm3 s-1), and zero-order (mol dm-3 s-1).
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Reaction kinetics relates reaction rate to concentration, temperature, surface area and catalysts. Questions cover rate laws, reaction order, rate constants, activation energy and the activated complex, including how a catalyst lowers the activation energy without changing the overall energy change or equilibrium position.
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