Topic 9: Kinetics I Flashcards
Collision theory, Maxwell-Boltzmann, catalysts, experiments to measure rate
Define rate of reaction
the change of concentration/amount of reactant or product, per unit of time
Collision theory
for a reaction to occur, particles must collide in the right direction, with right orientation, and the minimum amount of kinetic energy
Activation energy
the minimum amount of energy required for a reaction to occur
What does a Maxwell-Boltzmann distribution show?
Shows the energy in gas particles.
How does an increase in temperature affect the Maxwell-Boltzmann distribution?
- The peak shifts to the right, and becomes broader and lower
- The area beyond the Ea line increases
Why does rate increase when temperature increases?
Particles have more kinetic energy
They collide more frequently
They collide with more energy and therefore more collision have energy greater than or equal to the Ea
Why does an increase in concentration increase rate?
More reactant particles in a given volume
Therefore more frequent collisions
Why does an increase in surface area increase rate?
A larger SA means more surface exposed, so a larger site for collisions
Therefore higher frequency of collisions
How does a catalyst affect rate?
It speeds up rate, by reducing the activation energy by providing an alternative reaction pathway
What is a heterogeneous catalyst?
A catalyst in a different phase to the reactants
What is a homogeneous catalyst?
A catalyst in the same phase as the reactants
How does the heterogeneous catalyst work?
- Substances adsorb to the surface of the catalyst
- The bonds in the reactant weaken and break to form radicals
- The radicals react together to form new substances
- New molecules are released from the surface of the catalyst called desorption.
How does a catalyst affect the Maxwell-Boltzmann distribution?
The Ea line shifts to the left, as more particles have enough energy to react.
Why use catalysts?
- Lower temp needed for a reaction –> less money spent and less CO2 produced
- Speeds up reaction, so less money spent
- Changes properties of a product
Environmental reasons to use a catalyst
- Lower temp + pressure reduces energy required and CO2 produced
- Less waste as catalysts allow reactions to have better atom economies
