Rate of Reaction and Average rate - Chemical Kinetics

📘 Rate of Reaction and Average Rate in Chemical Kinetics

⚗️ What is Rate of Reaction?

The rate of a chemical reaction is the change in concentration of a reactant or product per unit time.

For a reaction: aA + bB → cC + dD

Rate = – (1/a) × d[A]/dt = – (1/b) × d[B]/dt = + (1/c) × d[C]/dt

📈 Graph of Rate of Reaction

The rate can be visualized using a graph:

• Reactants: curve goes down ⬇️
• Products: curve goes up ⬆️
• Slope = Reaction rate

📏 Units of Rate

The standard unit is mol·L^–1·s^–1.

It can change depending on the reaction order.

📊 Average Rate vs Instantaneous Rate

• Average Rate: Change in concentration over time interval.
• Instantaneous Rate: Slope of the curve at a specific point.

🔄 Rate of Appearance & Disappearance

Example for: A → B

• Rate of disappearance of A = – d[A]/dt
• Rate of appearance of B = + d[B]/dt

🧪 Example

Reaction: 2HI → H₂ + I₂

If rate of disappearance of HI is R:

• Rate of appearance of H₂ = R / 2
• Rate of appearance of I₂ = R / 2

📌 Summary

• Rate = Change in concentration / time
• Unit = mol·L^–1·s^–1
• Rate of disappearance is negative
• Rate of appearance is positive
• Graph slope = Instantaneous rate

Related article: Feasibility with Chemical Kinetics