Topic 9 - Kinetics 1
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What effect does temperature have on the rate of reaction?
increased temp = increased rate • increase in kinetic energy • particles move faster ∴ frequency of collisions increase • no. collisions with energy ≥ Ea increases
What effect does concentration/pressure have on the rate of reaction?
increased conc = increased rate • more particles ∴ frequency of collisions increase • no. collisions with energy ≥ Ea increases
What effect does surface area have on the rate of reaction?
increased SA = increased rate • more particles exposed to collide with other reactants • no. collisions with energy ≥ Ea increases
What factors affect collisions?
• orientation (atoms must face correct way when colliding in order to react) • activation energy (particles must collide with sufficient energy to break bonds) • steric hinderance (large atoms attached to central atom can hinder reacting species from attacking central atom)
rate =
[reactant] ________ time
rate ∝
Vf -Vt or 1/t
What do Maxwell-Boltzmann distribution curves show?
number of particles at any given energy total area under curve = total no. particles
How does an increase in temperature affect a Maxwell-Boltzmann distribution curve?
shifts peak right and down -total no. particles stays the same but more have energy ≥ Ea
How does an increase in concentration affect a Maxwell-Boltzmann distribution curve?
total area under curve increases (line is higher) -no. particles with energy ≥ Ea increases
How does a catalyst affect a Maxwell-Boltzmann distribution curve?
• lower Ea - no. particles with energy ≥ Ea increases
How do catalysts increase the rate of reaction?
• reduce the activation energy - by providing an alternative pathway to a low energy intermediate
What is a homogeneous catalyst?
a catalyst in the same phase (state) as the reaction
How does a homogeneous catalyst work?
• reacts with one of the reactants to form an intermediate • intermediate reacts with the other reactant(s) to reform the catalyst -avoids collisions between two negative particles (which would repel eachother so would need a lot of energy)
What is a heterogeneous catalyst?
a catalyst in a different phase (state) to the reaction
How does a heterogeneous catalyst work?
• provides an active site which reactants adsorb to (weakens bonds) • new bonds form and adsorbed reactants are changed into adsorbed product(s) • product(s) deadsorb, freeing the active site to be used again
What are enzymes?
biological catalysts that have an active site specific to a certain substrate -only work at a limited range of temperatures (otherwise will denature, changing the shape of the active site)