3.2.2 Reaction rates Flashcards
(19 cards)
Define collision theory.
For a reaction to occur, particles must collide with sufficient energy (activation energy) and the correct orientation.
How does increasing concentration affect rate of reaction?
Increases frequency of collisions between reacting particles, increasing the rate of reaction.
How does increasing pressure of a gas affect rate of reaction?
Increases the frequency of collisions as particles are closer together, increasing the rate of reaction.
How is rate of reaction calculated from a graph?
Rate = gradient = change in y/change in x = amount of product formed or reactant used / time.
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up in the overall reaction.
How does a catalyst affect activation energy?
Provides an alternative reaction pathway with a lower activation energy.
How is a catalyst represented in an enthalpy profile diagram?
A second curve is shown with a lower activation energy peak compared to the uncatalysed reaction.
Define a homogeneous catalyst.
A catalyst in the same physical state as the reactants.
Define a heterogeneous catalyst.
A catalyst in a different physical state from the reactants.
What are the economic benefits of catalysts?
Lower energy requirements reduce costs and increase rate of production.
What are the environmental benefits of catalysts?
Lower temperatures reduce energy demand and CO₂ emissions from burning fossil fuels.
Name methods for measuring reaction rate.
Measure change in mass, gas volume produced, or concentration over time.
What does the Boltzmann distribution show?
The distribution of molecular energies in a gas at a given temperature.
What does the area under the Boltzmann curve represent?
The total number of particles in the sample.
Where is activation energy shown on a Boltzmann curve?
It is marked as a vertical line; area beyond this line shows particles with sufficient energy to react.
What happens to the Boltzmann distribution when temperature increases?
The peak shifts lower and to the right; more molecules have energy ≥ activation energy.
How does a catalyst affect the Boltzmann distribution?
It does not change the shape but shifts the activation energy line to the left, increasing the proportion of molecules able to react.
What is a physical quantity that can be monitored to measure rate?
Gas volume, concentration, mass loss over time.
Why is sustainability important in using catalysts?
Catalysts reduce energy demand, conserving resources and lowering emissions, though toxicity must be considered.
