Does a catalyst get used up in a reaction?

No. A catalyst participates in the mechanism but is regenerated by the end of the catalytic cycle, so in principle a small amount can turn over a large quantity of reactant, though real catalysts can degrade or be poisoned over time.

Why does increasing temperature usually speed up reactions so dramatically?

The fraction of molecules with enough energy to cross the activation barrier grows exponentially with temperature, so even a modest temperature rise can multiply the rate, which is why many reactions roughly double in rate for each ten-degree increase.

Catalysis and Temperature Dependence

Reaction rates rise sharply with temperature in a way captured by the Arrhenius equation, and catalysts accelerate reactions by providing alternative pathways with lower activation barriers.

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Definition

Catalysis is the acceleration of a reaction by a substance that provides a lower-energy pathway and is regenerated unchanged, and temperature dependence refers to the Arrhenius relationship between the rate constant, the activation energy, and temperature.

Scope

This topic covers the temperature dependence of rate constants through the Arrhenius equation, the activation energy and pre-exponential factor, and their molecular interpretation by collision and transition state theories. It covers the kinetics of catalysis: how catalysts lower the activation barrier without being consumed, homogeneous and heterogeneous catalysis, the Langmuir-Hinshelwood and Eley-Rideal surface mechanisms, and enzyme catalysis through the Michaelis-Menten scheme. The detailed theory of the activated complex and the underlying rate laws are treated in sibling topics.

Core questions

How does the Arrhenius equation relate the rate constant to temperature and activation energy?
How does a catalyst increase the rate without being consumed or shifting equilibrium?
How do the Langmuir-Hinshelwood and Eley-Rideal mechanisms describe surface catalysis?
How does the Michaelis-Menten scheme account for enzyme kinetics and saturation?

Key concepts

Arrhenius equation and pre-exponential factor
Activation energy
Homogeneous and heterogeneous catalysis
Langmuir-Hinshelwood and Eley-Rideal mechanisms
Michaelis-Menten enzyme kinetics

Key theories

Arrhenius equation: The rate constant depends exponentially on the negative ratio of activation energy to thermal energy, so a plot of the logarithm of the rate constant against inverse temperature yields the activation energy from its slope.
Michaelis-Menten enzyme kinetics: An enzyme binds substrate in a rapid pre-equilibrium to form a complex that converts to product, giving a rate that rises with substrate concentration and saturates at a maximum velocity, characterized by the Michaelis constant.

Clinical relevance

These ideas underpin industrial heterogeneous catalysis such as ammonia synthesis and catalytic converters, the temperature control and stability of chemical processes and stored materials, and the quantitative analysis of enzymes that makes catalysis central to biochemistry and drug action.

History

Berzelius named catalysis in 1835; Arrhenius gave the temperature law of rates in 1889, and the early twentieth century saw Langmuir's surface kinetics and the Michaelis-Menten 1913 treatment of enzymes, establishing catalysis as a quantitative branch of kinetics.

Key figures

Svante Arrhenius
Jons Jacob Berzelius
Leonor Michaelis

Seminal works

atkins2018
laidler1987

Frequently asked questions

Does a catalyst get used up in a reaction?: No. A catalyst participates in the mechanism but is regenerated by the end of the catalytic cycle, so in principle a small amount can turn over a large quantity of reactant, though real catalysts can degrade or be poisoned over time.
Why does increasing temperature usually speed up reactions so dramatically?: The fraction of molecules with enough energy to cross the activation barrier grows exponentially with temperature, so even a modest temperature rise can multiply the rate, which is why many reactions roughly double in rate for each ten-degree increase.