Topic 9 - Kinetics I Flashcards
What are the two definitions of rate of reaction?
- How quickly the reactants are used up/ how quickly the products are formed
- The change of concentration of a reactant/product per unit time
What are the units for rate of a reaction?
moldm^-3s^-1
What type of graph can you plot to find the rate of reaction?
A concentration-time graph
What are the 5 factors that affect the rate of reaction?
- Temperature
- Surface Area of reactant
- Concentration
- Catalyst
- Pressure
What are the three assumptions of collision theory?
- The particles have to collide
- Particles must have at least the activation energy
- Particles must collide in the correct orientation
What are the 2 different ways that changes in rate of reaction due to changing conditions can be explained?
- Simple collision theory
- Boltzmann distribution curve
How would you explain the change in rate using simple collision theory when the concentration of a reactant is changed?
- More particles in a given volume
- More frequent collisions
- Higher rate of reaction
How would you explain the change in rate using simple collision theory when the surface area of a reactant is changed?
- Particles have more kinetic energy
- Therefore, particles move faster so collide more frequently AND more particles have an energy that is greater than the activation energy of the reaction
- A greater proportion of collision are successful
- Higher rate of reaction
How would you explain the change in rate using simple collision theory when the temperature is changed?
- More available particles to collide with
- Increased frequency of collisions
- Higher rate of reaction
What does the area under the line of a Boltzmann Distribution curve show us?
The total number of particles
How would you explain the change in rate using Boltmann’s distribution when the temperature is changed?
- The curve is shifted to the right with the peak lower but the bottom of the curve plateauing higher -> the area under the graph remains constant
- Larger area under the graph that is to the right of the activation energy line
- An increase kinetic energy of the particles
- Area under the curve above the activation energy is larger at higher temperatures so a greater proportion of particles have E >= Ea
- Increased proportion of successful collisions
- Particles are also moving faster so there si an increased frequency of collisions
How would you explain the change in rate using Boltmann’s distribution when a catalyst is added?
- Catalyst provides an alternate pathway with a lower activation energy for a reaction to proceed via
- Increased area to the right of the activation energy line meaning that a greater proportion of particles have the required activation energy
- Increased proportion of successful collisions
How do you find the rate of reaction at different points on a concentration - time graph?
Take the gradient at that point
What are the two types of catalyst?
Heterogenous and Homogenous
What is the definition of a heterogenous catalyst?
The reactants and catalyst are in a different physical state
What is the definition of a homogenous catalyst?
The reactants and catalyst are in the same physical state
Describe how heterogenous catalysts work?
- The reactant molecule approaches the catalyst and is adsorped onto its active site
- The bonds are weakened allowing rearrangement of atoms to occur
- The products are released from the surface - desorped
What is the heterogenous catalyst used in the Haber process?
Iron
What is the heterogenous catalyst used in the contact process?
V2O5
What is the heterogenous catalyst used in Hydrogenation?
Nickel
In what way do catalysts benefit the environment?
- Lower temperatures can be used for reactions
- Less energy is required therefore, less GHG’s produced
In what away are catalyst economically beneficial?
- Allows lower temperatures to be used
- Less money spent on heating
- The catalyst can be reused therefore, you don’t have to keep repurchasing it
