Chapter 8: Reaction Kinetics Flashcards
(15 cards)
Define rate of reaction.
Rate of reaction = change in concentration of reactant or product per unit time (mol dm⁻³ s⁻¹).
Describe collision theory.
Reactions occur when particles collide with:
* Sufficient energy (≥ activation energy)
* Correct orientation
What factors affect the rate of reaction?
- Concentration/pressure: More particles = more collisions
- Temperature: Increases kinetic energy → more particles with enough energy to react
- Surface area: More exposed particles = more frequent collisions
- Catalyst: Lowers activation energy, increasing rate
- Light (for photochemical reactions)
Explain how higher temperature affects reaction rates using collision theory.
Higher temperature = more energetic collisions = higher reaction rate.
What methods can be used to measure reaction rate?
- Measuring volume of gas produced (e.g., using gas syringe)
- Measuring loss of mass
- Monitoring color change with colorimeter
- Timing precipitate formation (e.g., “disappearing cross” experiment)
How do you interpret graphs of rate vs time?
- Steep slope = fast rate
- Curve flattens as reactants are used up
- Tangent at a point gives instantaneous rate
Define the rate equation.
Rate = k[A]^m[B]^n, where:
* k = rate constant
* m, n = orders of reaction (can be 0, 1, or 2)
* Overall order = m + n
How can you determine reaction order from experimental data?
- Zero order: rate doesn’t change when concentration changes
- First order: rate ∝ [A]
- Second order: rate ∝ [A]²
How do you calculate the rate constant k?
k = rate / ([A]^m[B]^n)
What is the initial rates method?
Compare changes in concentration and rate between experiments to deduce orders.
Define half-life (t½).
Time taken for the concentration of a reactant to halve.
How does constant half-life indicate first-order kinetics?
In a first-order reaction, the half-life is constant regardless of concentration.
What is activation energy (Ea)?
Minimum energy required for a reaction to occur.
Explain how a catalyst works.
Provides an alternative reaction pathway with a lower activation energy.
What should be highlighted in energy profile diagrams with and without a catalyst?
Highlight the reduced activation energy.
