Chemical Kinetics

Concept: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It provides an alternative reaction pathway with different energy requirements. Effect on Activation Energy:

• A catalyst lowers the activation energy ( ) of a reaction.
• It provides an alternative pathway with a lower energy barrier.
• As a result, more reactant molecules acquire sufficient energy to undergo reaction, increasing the reaction rate.

Effect on Enthalpy Change ( ):

• A catalyst does not change the enthalpy change of the reaction.
• The initial and final energy states of reactants and products remain the same.
• Since depends only on these energy states, it remains unaffected.

Conclusion: Thus, a catalyst speeds up a reaction by lowering activation energy but does not alter the enthalpy change or thermodynamics of the reaction.

Concept: A first-order reaction is one in which the rate of reaction is directly proportional to the concentration of a single reactant. The integrated rate equation relates concentration with time and helps determine reaction kinetics.
Step 1: Rate law for first-order reaction Consider a reaction: For a first-order reaction, where:

• = concentration of reactant at time
• = rate constant

Step 2: Rearranging the equation
Step 3: Integration Integrate both sides: where is the integration constant.
Step 4: Applying initial condition At , concentration Substitute back:
Step 5: Final integrated rate equation Alternative forms: Using base-10 logarithm: Conclusion: Thus, the integrated rate equation for a first-order reaction is: which shows that concentration decreases exponentially with time.