10) Reaction rates and equilibrium Flashcards
Define rate of reaction
the change in concentration of a reactant or product in a given time
rate = ?
change in conc. / time
When is rate fastest?
at the start of a reaction as each reactant is at its highest concentration
What is rate affected by?
conc. (pressure if gaseous)
temperature
use of catalysts
surface area of solid reactants
Define collision theory
two reacting particles must collide for a reaction to occur, and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction
How does an increase in concentration affect rate?
increases no. of particles in the same volume
particles are closer together and collide more frequently in a given time
there will be more effective collisions and an increase in rate of reaction
When gas is compressed into a smaller volume, and pressure is increased what happens to the concentration of gas molecules?
increases as the same no. occupy a smaller volume
How can the progress of a chemical reaction by followed?
monitoring the removal of a reactant or the formation of a product
Name two ways rate of reaction can be measured for reactions that produce gases?
monitoring volume of gas produced at regular time intervals using gas collection
monitoring the loss of mass of reactants using a balance
either of these measurements are then plotted against time and a tangent drawn for initial rate
What apparatus is used for monitoring volume of gas produced at regular time intervals using gas collection?
conical flask delivery tube trough filled with water measuring cylinder, filled with water and held upside down in trough with clamp stop watch alternative: gas syringe
How can you tell the reaction is compete when monitoring the loss of mass of reactants using a balance?
no more mass is lost, remains constant
Define catalyst
a substance that increases the rate of a chemical reaction without being used up in the process
What does a catalyst do?
provides can alternative route for the reaction with lower activation energy
may react to form an intermediate or provide a surface on which the reaction can occur but is regenerated at the end
Describe homogenous catalysts
same physical state as reactants and reacts to form an intermediate, which then breaks down to give the product and regenerate the catalyst
Describe heterogeneous catalysts
different physical states from reactants
usually solids in contact w/ reactants (g/aq) which are adsorbed (weakly bonded) onto their surface where the reaction takes place. after the product molecules leave the surface by desorption
Name 4 common catalysts and their uses in industry
Fe (s) - Haber process
Pt / Rh (s) - reforming
Ni (s) - hydrogenation of alkenes
V2O5 (s) - contact process (making SO3 for sulfuric acid)
Describe catalytic converters
have large surface area for heterogeneous catalysts to convert harmful exhaust gases into less harmful ones which can be released into the atmosphere
Comment on the use catalysts with regards to sustainability
increase the rate of reaction by lowering Ea
reduces temp. and energy requirements
less electricity / finite fossil fuels used
increases profits and less pollutants linked to global warming
Give the x and y axis of a Boltzmann distribution
x = energy y = no. of molecules with a given energy
Describe a Boltzmann distribution showing temperature
at a higher temperature peak is lower and shifted right
greater proportion of molecules can overcome Ea / have energy greater than or equal to Ea
a greater proportion of collisions will lead to a reaction
increases rate of reaction
more frequent collisions as molecules are moving faster also
Describe a Boltzmann distribution showing catalyst use
Ea with catalyst (left hand side) and without catalyst labelled
a catalyst provides an alt. reaction route w/ a lower Ea
greater proportion of molecules have energy greater than or equal to lower Ea
on collision more molecules will react
increases rate of reaction
Define reversible reaction
a reaction that takes place in both forward and reverse directions
Define 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 the concentrations do not change
Define position of equilibrium
the relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium
Define 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 the change and to restore equilibrium
If there are more products formed, the position of equilibrium has shifted to the _ and If there are more reactants formed, the position of equilibrium has shifted to the _?
right-hand side
left-hand side
An increase in temp. results in a shift in the _ direction (ΔH is _ ) and a decrease in temp. results in a shift in the _ direction (ΔH is _)?
endothermic
positive
exothermic
negative
An increase in pressure results in a shift in the direction of the _ and a decrease in pressure results in a shift in the direction of the _?
fewer gas molecules
more gas molecules
A catalyst doesn’t change _ - its speeds up the rate of forwards and reverse reactions equally?
position of equilibrium
Define equilibrium constant Kc
a measure of the position of equilibrium, the magnitude of an equilibrium constant indicates whether there are more reactants or more products in an equilibrium system
Kc = ?
[products] / [reactants]
concentrations at equilibrium
^no of molecules
What does Kc = 1 indicate?
position of equilibrium halfway between reactants and products
What does Kc > 1 indicate?
position of equilibrium towards products
What does Kc < 1 indicate?
position of equilibrium towards reactants
The larger the value of Kc, the further the equilibrium lies to the _ and the greater the concentration of _?
RHS
products to reactants
