Chapter 10 - Reaction rates and Equilibrium Flashcards
Define Activation Energy
The minimum energy required to start a reaction by the breaking of bonds
What does rate of reaction measure (2)
How fast a reactant is being used up
or
how fast a product is being formed
What features can affect rate of reaction?
Concentration or pressure
Temperature
Use of a catalyst
Surface area of solid reactants
What does the collision theory state?
That 2 reacting particles must collide for a reaction to occur.
What are the 2 conditions reacting particles have to meet for a successful collision?
The particles have sufficient energy to overcome the activation energy barrier of the reaction
The particles collide with the correct orientation
What is the equation for rate of reaction?
Rate (moldm-3s-1) = change in concentration (moldm-3)/
Time (s)
What happens to rate of reaction when the concentration of a reactant is increased? Why?
The rate increases because the number of particles in the same volume increases and therefore particles are closer together and will collide more frequently. In a given time there will therefore be more effective collisions and the rate of reaction will increase
What happens to rate of reaction when the pressure of a reactant is increased? Why?
The rate increases because the same number of particles are compressed into a smaller volume and therefore particles are closer together and will collide more frequently. In a given time there will therefore be more effective collisions and the rate of reaction will increase
What are the 2 methods for following the progress of a reactiopn?
Monitoring the removal of a reactant (decease in concentration)
Monitoring the formation of a product (increase in concentration)
What is one method of determining rate of reaction for a reaction that produces gases?
How would you record this data?
Monitoring the volume of gas produced at regular intervals by collecting the gases formed.
Use a water trough and an upside down measuring cylinder filled with water, connected to a conical flask where the reaction is taking place by a delivery tube to measure the gas formed.
Time(x) against volume of gas produced (y)
What is another method of determining rate of reaction for a reaction that produces gases?
How would you record this data?
Monitor the mass loss of the reactant using a balance. Mass lost (y) against time (x)
What is a catalyst and what does it do?
A catalyst is a substance that changes the rate of reaction without undergoing any permanent change itself
How does a catalyst increase the rate of reaction?
It provides an alternative reaction pathway with a lower activation energy
What are the types of catalysts?
Homogeneous
Heterogeneous
What is a homogeneous catalyst? What does it do?
A catalyst with the same physical state as the reactants. It reacts with the reactants to form an intermediate which then breaks down to give the products and regenerates the catalyst
What are homogeneous catalysts used for? (2) and in each case what is the catalyst
Making esters - sulfuric acid
Ozone depletion - Cl radicals
What is a heterogeneous catalyst and what does it do?
It is a catalyst that has a different physical state to the reactants. The reactant molecules are weakly bonded (adsorbed) onto the surface of the catalyst where a reaction occurs. The product molecules are then desorbed from the catalyst. The catalyst is usually a solid in contact with gaseous or aqueous reactants
What are heterogeneous catalysts used for? (2) and in each case what is the catalyst
Making ammonia via the haber process - solid Iron
Hydrogenation of alkenes Ni(s)
What are the positives to the use of catalysts? (4)
Lower production costs as temperatures requirements are reduced
More products can be produced more quickly using less energy - increases profitability
It lowers the temperatures, reducing the demand for fossil fuels so less CO2 is emitted
Better atom economy (reduces wastage and pollutants
What are the negatives to the use of catalysts? (4)
Some catalysts are toxic so need to be disposed of carefully
Catalysts can be very specific and only catalyse one reaction
Catalysts can be very expensive
Some catalysts are poisoned by impurities and will become inefficient over time
What does the Maxwell Boltzmann distribution graph show?
The energy distribution of all molecules in a gaseous state
Describe the basics of a Maxwell Boltzmann distribution graph
The number of molecules is on the Y axis
The energy is on the X axis
The activation energy is represented by a vertical line coming up from the energy
Where does the curve start on a Maxwell Boltzmann distribution graph?
At the origin (0,0)
What does the area under the Maxwell Boltzmann distribution graph give?
The total number of molecules
What does the peak on the Maxwell Boltzmann distribution graph show?
The most likely energy of any molecule
What happens if you use a catalyst in a reaction and how is this shown on a Maxwell Boltzmann distribution graph?
Provides an alternative energy pathway which lowers the activation energy which means more molecules have sufficient energy to react when they collide. This is represented as a vertical line from the X axis but is a smaller energy and is therefore closer to the y axis than the activation energy without a catalyst
At a higher temperature what happens to the most likely energy of any molecule?
It will increase (meaning the peak will be further from the Y axis at a higher energy)
What happens to the area of the Maxwell Boltzmann distribution graph when the temperature increases?
It remains the same because no new molecules have been introduced
When at a higher temperature what happens to the number of molecules that have energy equal to or greater than the activation energy?
It increases because molecules have more energy
What happens to the number of collisions at a higher temperature?
It increases in frequency because the molecules have more energy and will collide more often due to moving more
What happens to the rate of reaction at higher temperatures?
It INCREASES due to an increase in energy of molecules and an increase in the frequency of collisions
What conditions are required for dynamic equilibrium to be achieved?
Closed system with a reversible reaction
Define closed system
A system where reactants and products are isolated from their surroundings so their temperature, pressure and concentrations remain unaffected by outside influences.
Define dynamic equilibrium
exists in a closes system where the rate of the forwards reaction is equal to the rate of the reverse reaction and the concentrations of the products and reactants has not changed
List 4 features of dynamic equilibrium
the concentrations of the products and reactants does not change
the rate of the forward reaction equals the rate of the backwards reaction
it is in a closed sytem
there is no change in macroscopic properties
What 3 physical changes can be predicted by Le Chatelier’s principle?
Change in temperature
Change in pressure
Change in concentration
What does Le Chatelier’s principle state?
when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
What happens to the position of equilibrium if the concentration of a product is increased?
The equilibrium will shift to the left to form more reactants
What happens to the position of equilibrium if the concentration of a reactant is increased?
The equilibrium will shift to the right to form more products
What happens to the equilibrium if pressure is increased?
Equilibrium shifts to the side with fewer molecules
What happens to the position of equilibrium if pressure is decreased?
Equilibrium shifts to the side with more molecules
What happens to the position of equilibrium if pressure is increased or decreased in a reaction which has the same number of molecules on both sides?
There will be no effect on the position of equilibrium because there are the same number of molecules on either side
What happens to the position of equilibrium if temperature is decreased in a exothermic reaction?
It shift to the exothermic side which is the product side
What happens to the position of equilibrium if temperature is increased in an exothermic reaction?
It shift to the endothermic side which is the reactant side
What happens if the position of equilibrium if temperature is increased in an endothermic reaction?
It shift to the endothermic side which is the product side
What happens to the position of equilibrium if temperature is decreased in an endothermic reaction?
It shift to the side exothermic side which is the reactant side
Do catalysts affect the position of equilibrium?
No but it increases the rate of the forwards and reverse reaction equally.
How can the position of equilibrium be calculated?
Using the equilibrium law where you use the concentrations of products and reactants at equilibrium
If the value of equilibrium constant is 1 what does it mean about the position of equilibrium?
It is halfway between the products and reactants
If the value of equilibrium constant is less than 1 what does it mean about the position of equilibrium?
It is towards the reactant side
If the value of equilibrium constant is more than 1 what does it mean about the position of equilibrium?
It is towards the product side
What is an equilibrium constant?
The actual position of equilibrium
