Chapter 10 - Reaction Rates and Equilibrium Flashcards
Reaction rates, Catalysts, Boltzmann distribution, Dynamic equilibrium and le Chatelier's principle, and The equilibrium constant.
What is reaction rate?
The change in concentration of a reactant or product in a given time.
What makes an effective collision?
Particles must have sufficient energy
Particles must collide in correct orientation
Which factors can change the rate of a chemical reaction?
Concentration
Temperature
Use of a catalyst
Surface area of solid reactants
What effect does increasing temperature have on reaction rate?
Reaction rate increases
Explain why increasing temperature has its effect on reaction rate
Particles have more energy
Higher speed
Collide more frequently
More successful collisions
Rate increases
What is the rule of thumb for reaction rate and temperature?
A 10C increase in temperature doubles the rate.
What effect does increasing concentration/pressure have on reaction rate?
Reaction rate increases
Explain why increasing concentration/pressure has its effect on reaction rate
Concentration increases
More particles per unit volume
More frequent collisions
More successful collisions
Rate increases
How can progress of a chemical reaction be followed?
Monitoring the removal of a reactant.
Following the formation of a product.
What are the two methods of determining reaction rate, when a gas is produced?
Monitoring the volume of gas produced
Monitoring the loss of mass of reactants
What does a catalyst do?
A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.
What are the main properties of a catalyst?
Not used up in the reaction.
May react with a reactant to form an intermediate or provide a surface for the reaction to take place.
The catalyst is regenerated at the end of the reaction.
What is a homogeneous catalyst?
Has the same physical state as the reactants.
How does a homogeneous catalyst interact with the reactants?
The catalyst reacts with the reactants to form an intermediate.
The intermediate then breaks down to give the product and regenerates the catalyst
Give two examples of homogeneous catalysts
Sulphuric acid in the production of esters
Chlorine radicals in ozone depletion
What is a heterogeneous catalyst?
Has a different physical state from the reactants.
How does a heterogeneous catalyst interact with the reactants?
Heterogeneous catalysts are usually solids in contact with gaseous reactants or reactants in solution.
Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place.
After the reaction, the products leave the surface of the catalyst by desorption.
Give examples of heterogeneous catalysts
Iron in making ammonia
Platinum or rhodium in reforming Nickel in hydrogenation of alkenes
Vanadium oxide in the making sulfur trioxide
What are the benefits of using a catalyst?
Lowers activation energy
Less electricity used
Product made faster and cuts costs and increases profit
Less fossil fuels used cuts emissions of carbon dioxide
What are the main features of Boltzmann distribution?
No molecules have zero energy
Area under the curve is equal to the number of molecules
No maximum energy
How does a Boltzmann distribution curve change when temperature is increased?
The peak is lower and shifted to the right
A greater proportion of molecules can overcome the activation energy
How does a Boltzmann distribution show the effect of a catalyst?
Activation energy with a catalyst is lower than normal activation energy.
Therefore a greater proportion of molecules exceed the new lower activation energy.
What is a dynamic equilibrium?
The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change.
What is le Chatelier’s principle?
When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.
What is the effect of a catalyst on equilibrium?
Does not change the position
Speeds up the rates of forward and reverse reactions equally
If a reversible reaction is shown as: aA + bB cC + dD how is Kc worked out?
Kc = [C]^c x [D]^d / [A]^a x [B]^b
