1. Collision Theory and Activation Energy:
* Collisions: Reactions happen when molecules collide with sufficient energy to break existing bonds and form new ones.
* Activation Energy (Ea): This is the minimum energy required for molecules to react.
* Temperature's Role: Higher temperatures increase the average kinetic energy of molecules, leading to:
* More frequent collisions: Molecules move faster and collide more often.
* Higher energy collisions: More collisions have enough energy to overcome the activation energy barrier.
2. The Arrhenius Equation:
This equation mathematically quantifies the relationship between temperature and reaction rate:
* k = A * exp(-Ea/RT)
* k: Rate constant (a measure of reaction speed)
* A: Pre-exponential factor (related to collision frequency)
* Ea: Activation energy
* R: Ideal gas constant
* T: Temperature in Kelvin
3. Impact on Reaction Order:
While temperature doesn't directly change the reaction order (which is determined by the stoichiometry and mechanism), it can indirectly influence it in several ways:
* Faster Rates: Higher temperatures generally lead to faster reactions. This can make it harder to determine the reaction order experimentally, as reactions may proceed too quickly to accurately measure the rate.
* Shifting Equilibrium: For reversible reactions, temperature changes can shift the equilibrium position, leading to a change in the apparent order at different temperatures.
* Competing Reactions: If multiple reactions occur simultaneously, temperature can influence the relative rates of these reactions, affecting the overall observed reaction order.
4. Examples:
* Decomposition of N2O5: This reaction is first-order. Increasing temperature significantly increases its rate, but the order remains the same.
* Hydrogenation of Ethylene: This reaction is zero-order at high temperatures due to the surface saturation of the catalyst. Lowering temperature can change the order as the surface becomes less saturated.
In summary:
Temperature is a powerful factor influencing reaction rates. It doesn't change the reaction order itself but can significantly impact how we measure and understand the order through its influence on collision frequency, activation energy, and the relative rates of competing reactions.
