What is Reaction Kinetics?
Reaction kinetics is the study of how fast chemical reactions occur and what factors control their speed. It explores activation energy, collision theory, and why some reactions are instantaneous while others take hours.
Reaction kinetics examines the rate of reaction (speed) and the mechanism (steps). Key factors are concentration, temperature, surface area, and catalysts. The activation energy E_a is the minimum energy barrier molecules must overcome to react.
Step-by-step worked examples
If temperature increases by 10°C, reaction rate often roughly doubles. Why?
Higher temperature → molecules move faster Collisions are more frequent and energetic More collisions exceed the activation energy E_a Reaction rate doubles (rule of thumb: +10°C ~ ×2 rate)
Catalyst is added to a reaction. Effect on activation energy and rate?
Catalyst provides an alternative reaction pathway Alternative pathway has lower E_a (no catalyst needed) Same E_a not reached → more molecules can react Rate increases; catalyst unchanged at end
Grinding a solid reactant into powder. Effect on reaction rate?
Increases surface area of solid More surface exposed to other reactants More collisions per unit time Reaction rate increases
Flashcards
Quick quiz
Q1.Activation energy E_a is:
Q2.Adding a catalyst will:
Q3.If concentration of reactant A doubles, rate typically:
Q4.Grinding a solid increases reaction rate because:
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Common mistakes
Thinking catalyst is consumed or changes the equilibrium. — Correct: Catalyst speeds rate but is regenerated and doesn't shift equilibrium.
Confusing rate law with stoichiometry. — Correct: Stoichiometry from equation; rate law from experiment.
Assuming all reactions speed up the same with temperature. — Correct: Temperature increase speeds all reactions but by different factors (depends on E_a).
Thinking lower E_a means reaction is less favorable. — Correct: Lower E_a means FASTER (kinetics); ΔG determines favorability (thermodynamics).
FAQ
What is reaction kinetics?
Study of reaction rates (how fast reactions go) and factors that affect speed: temperature, concentration, surface area, catalyst.
What factors increase reaction rate?
Higher temperature, higher concentration, larger surface area, presence of catalyst.
Does catalyst appear in the balanced equation?
No — catalyst is not consumed, so it doesn't appear in net equation.
Can a reaction with high E_a ever be fast?
Yes, if temperature is very high — higher T gives molecules more energy to cross E_a.