Introduction:

The rate of a chemical reaction depends on various factors, including temperature. Generally, an increase in temperature results in an increase in the reaction rate. This is because higher temperatures provide more energy to reactant molecules, leading to more frequent and effective collisions. The relationship between temperature and reaction rate is quantitatively described by the Arrhenius equation.



Effect of Temperature on Reaction Rate:

The speed of a reaction increases with temperature due to:

• Increased kinetic energy of reactant molecules.

• Higher collision frequency.

• Greater fraction of molecules possessing energy equal to or greater than the activation energy.

The Arrhenius Equation:

The Arrhenius equation mathematically expresses how reaction rate constants vary with temperature:

k = A e^(-Ea/RT)

Where:

• k = rate constant

• A = pre-exponential factor

• Ea = activation energy

• R = universal gas constant (8.314 J/mol·K)

• T = temperature (in Kelvin)

Activation Energy and Temperature Relationship:

Activation energy (Ea) is the minimum energy required for reactants to convert into products.

• At lower temperatures, fewer molecules have sufficient energy to overcome the activation barrier.

• At higher temperatures, a larger proportion of molecules exceed the activation energy, resulting in a faster reaction.

Temperature Coefficient and Rule of Thumb:

The temperature coefficient expresses how much the reaction rate changes with a 10°C rise in temperature. Generally, for most reactions:

Rate at (T+10)°C ≈ 2-3 × Rate at T°C

This means that for every 10°C increase in temperature, the reaction rate approximately doubles or triples.

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Graphical Representation of Arrhenius Equation:

A logarithmic form of the Arrhenius equation is:

ln k = ln A - (Ea/R) × (1/T)

Plotting ln k vs. 1/T results in a straight-line graph with slope -Ea/R, which helps determine the activation energy experimentally.

Practical Applications of Temperature Dependence of Reaction Rate:

• Industrial Reactions: Optimizing temperature conditions in chemical manufacturing (e.g., Haber process for ammonia production).

• Biological Systems: Enzyme-catalyzed reactions are highly temperature-sensitive.

• Storage of Medicines and Food: Lowering temperature slows down degradation reactions.

• Explosives and Combustion: Reactions are accelerated at higher temperatures, leading to controlled or uncontrolled explosions.

Conclusion:

Temperature significantly affects reaction rates by influencing molecular energy and collision frequency. The Arrhenius equation provides a mathematical framework to understand this dependency. By controlling temperature, chemical processes can be optimized for efficiency in industrial and biological applications.