Chapter 10 - Reaction Rates And Equilibrium Flashcards
Define rate of reaction
Measures how fast a reaction is used up or how fast a product is being formed
Calculate the rate of reaction
Rate = change in concentration / time
Describe the general concentration-time graph
- rate is faster at the start, as reactants is at its highest concentration
- rate slows down the reaction as the reactants are being used up and their concentration decrease
- once one of the reactants has been completely reacted, the concentration stops changing
- rate of reaction is zero
Affecting the rate of reaction: • • • •
- concentration
- temperature
- catalyst
- surface area
What is the collision theory?
Two reacting particles must collide for a reaction to occur
What two conditions have to be met for an effective collision?
- the particle collide with the correct orientation
* the particles have sufficient energy to overcome the Ea barrier of reaction
How does the concentration affect the rate of reaction?
Increase concentration, increase rate of reaction due to increase number of particles in same volume. Particles are closer so frequently collide. More effective collisions.
How does increasing the pressure of gas affect the rate of reaction?
Increasing pressure, increases rate of reaction as gas is in smaller volume the concentration increases. Frequent effective collisions
How can you follow the progress of a reaction?
- monitoring the removal of a reactants
* following the formation of a product
Two ways to determine the rate of reaction when a gas is formed?
- monitoring the volume of gas produced at regular time intervals (gas collections)
- monitoring the loss of mass of reactants using a balance
Define a catalyst
A substance that changes the rate of reaction without undergoing permanent change
What are the three main characteristics of a catalyst?
- catalyst is not used up in chemical reaction
- may react with a reactant to form an intermediated / provide a surface for the reaction to take place
- is regenerated at the end of a reaction
Why does a catalyst increase the rate of reaction?
Provides an alternative reaction pathway of lower activation energy
What are the two types of catalyst?
- homogeneous catalyst
* heterogeneous catalyst
What is a homogeneous catalyst?
The same physical star as the reactants. The catalyst reacts to form an intermediate breaking down to give the product and regenerate the catalyst
Define the intermediate
A species formed during a reaction that reacts further and is not present in the final products
What is a heterogeneous catalyst?
Has a different physical state from the reactants. (Usually solid in contact with gaseous reactants).
Reactants are absorbed onto the surface of the catalyst where reaction takes place. Produces leave the the surface of the catalyst by desorption
Why is a catalyst a sustainability and economic importance?
- increase rate of reaction - lowering Ea - reduces the temperature
- decreases expensive
- requires less fossil fuels - less pollutants - decreasing CO2
What is the Boltzmann distribution showing if the graph?
Shows the number of molecules distributed to the molecules energy leaves
What are the features shown on the boltzamann distribution?
- no molecules have zero energy - curve starts at the origin
- area under the curve = number of molecules
- no maximum energy for a molecule - curve doesn’t meet at x-axis at high energy
Describe using Boltzmann distribution for a higher temperature
More molecules have an energy greater than or equal to Ea. Greater proportion of collision, increase rate of reactions. Collisions is more frequent as molecules are moving faster
How does a catalyst affect the Boltzmann distribution?
Catalyst provides alternative tour with lower Ea. Using a catalysed means a greater proportion of molecules have energy greater or equal than the lower Ea. More molecules will react to form a product.
What is a dynamic equilibrium ?
The rate of the forward and reverse reaction is the same. The concentrations of the reactants and products don’t change.
Define Le Chateliers Principle
When a system I’m equilibrium is subjected to an external change the system readjusts itself minimise the effect of change
What effect does the concentration change in a equilibrium?
Changing the concentration changes the rate of the forward/reverse reaction
How does the equilibrium change if more products are formed?
Shifts to the right
How does the equilibrium change if more reactants are formed?
Shifts to the left
What does the shift in the equilibrium depend on if temperature change?
The sign of 🔺H
Is the 🔺H positive or negative if an increase in temperature shifts the equilibrium position in the endothermic direction?
Positive
Is the 🔺H positive or negative if an decreases in temperature shifts the equilibrium position in the exothermic direction?
Negative
If the forward reaction is exothermic how does the increase temperature effect the equilibrium?
- position of equilibrium shifts to the left
* more reactants are made
If the forward reaction is endothermic how does the increase temperature effect the equilibrium?
- position of equilibrium shifts to the right
* more products are made
If the forward reaction is exothermic how does the decrease temperature effect the equilibrium?
- position of equilibrium shifts to the right
* more products are made
If the forward reaction is endothermic how does the decrease temperature effect the equilibrium?
- position of equilibrium shifts to the left
* more reactants are made
How does the increase in pressure effect the equilibrium?
Shifts the position of equilibrium to the side with fewer molecules (reducing the pressure of the system)
How does a catalyst effect the equilibrium?
Doesn’t effect the change in position. Just speeds up the rate of reaction.
The Haber process, what could be done to maximise the yield of ammonia?
- low temperature -> shifts to the right
* high pressure -> shifts to the right
Why doesn’t the Haber process use this conditions to maximise yield?
- low temperature -> slow reaction
- high temperature -> strong container needed + large quantities of water + increase costs + possible leaking of toxic hot gases
What catalyst is used in the Haber process?
Iron
What is a catalyst?
A substance that speeds up a reaction by providing an alternative route with a lower activation energy. At the end of the reaction, the catalyst is regenerated
How would you measure the rate of reaction between calcium carbonate and hydrochloric acid?
Add the reactants to a conical flask, which is upon a balance
Record the mass of the flask initially and at regular intervals
The reaction is complete when no more mass is lost
How would you work out the rate of reaction from a graph?
Draw a tangent against the curve and find the gradient
Gradient = dy / dx
This is the rate of reaction at that time
How would you measure the rate of reaction of the decomposition of hydrogen peroxide?
Place the hydrogen peroxide in a conical flask attached to a gas syringe
Add some manganese dioxide, which acts as a catalyst
Record the volume of gas in the cylinder at regular intervals
When no more gas is produced, the reaction has finished
How does increasing the pressure of a gas increase the rate of reaction?
An increase in pressure means that volume decreases. There is, therefore, the same number of particles but in a smaller area, which means that they are closer together and successful collisions are more common
How does increasing the concentration of particles increase the rate of reaction?
Increasing the concentration increases the number of particles in the same volume. This means that they are closer together and so will collide much more frequently, so there are more chances to react
What are the two characteristics of a successful collision?
The particles collide with the correct orientation
They collide with sufficient energy
