Topic 6: Kinetics Flashcards
Define rate of reaction
Rate of reaction is the change in concentration of reactants or products per unit time
Reaction concentration decreases over time
Product concentration increases over time
How to calculate instantaneous rate of reaction from a graph
First draw tangent to a curve at a specific time (if we are calculating the initial rate, draw the tangent from 0s)
Measure the gradient of the tangent (rise over run)
The gradient of the tangent is equal to the rate of reaction
How does the rate of reaction change over time
The initial rate of reaction is the fastest as there is a high concentration of reactant particles resulting in a high frequency of collisions between reactant particles
The rate of reaction decreases with time as the concentration of reactant particles decreases which results in a decrease in the frequency of collisions between reactant particles
Maxwell-Boltzmann energy distribution curve
Shows the number of particles with a particular value of kinetic energy
Collision theory
Collision theory states that reactant particles must collide with eachother to have a chemical reaction. These particles must satisfy two conditions:
- They must collide with energy equal to or grater than the activation energy of the reaction
- They must collide with the correct orientation
Activation energy
The minimum energy that colliding particles need in order to have a successful collision that results in a chemical reaction
Factors that affect the rate of reaction
- Temperature
- Concentration
- Particle size
- Pressure
- Catalyst
How does increasing temperature affect rate of reaction?
Refer also to Maxwell Boltzmann
Increasing the temperature of a reaction increases the rate of reaction.
This is because it increases the average kinetic energy of the particles - meaning that there are more collisions and these collisions are more likely to have activation energy greater than or equal to the activation energy
At a higher temperature, the peak of the Maxwell Boltzmann is lower and shifted to the right
How does increasing concentration of reactants affect rate of reaction?
Increasing the concentration of reactants increases the rate of reaction.
This is because the increased concentration leads to an increase in the frequency of collisions between reactant particles.
How do changes in particle size affect rate of reaction?
As particle size decreases, the rate of reaction increases - because smaller particles have larger surface areas which result in an increase in the frequency of collisions between reactant particles
e.g large chunks react slower than fine powders because powders have more surface area
How does increasing pressure affect rate of reaction?
For reactions that involve gases, increasing pressure increases the rate of reaction
At higher pressures the gas is compressed which has the effect of increasing its concentration’
This results in an increase in the frequency of collisions between reactant particles
Catalysts
Also refer to M.B curve
A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy.
The use of a catalyst shifts the activation energy line to the left on the M.B curve
