A2 - Unit 2 - Rates, equilibrium and pH Flashcards
How do you calculate rate?
Time
Or
Change in time
What is rate of reaction?
The change in concentration of a reactant or product per unit time
Why does the rate of reaction slow down as the reaction proceeds?
Fewer collisions take place per second between reactant particles
The rate slows down
What is the initial rate of reaction?
The change in concentration of a reactant or product per unit time at the start of the reaction when t=0
What can you use to measure pH changes for reactions involving acids or bases?
pH changes by carrying out titrations
pH changes by using a pH meter
What can you measure when trying to produce a rate graph?
Change in volume or pressure
The loss in mass or reactants
When performing reactions that produce visual changes what can you observe?
The formation of a precipitate
A colour change
What is the rate equation?
rate = k[A]m[B]n
where:
m = the order of reaction with respect to A
n = the order of reaction with respect to B
What is order?
With respect to a reactant is the power to which the concentration of the reactant is raised in the rate equation
What is overall order?
The sum of the individual orders m+n
What is the rate constant?
The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation
What happens to the reaction when there is a greater concentration?
The larger the number of collisions per second
the faster the reaction
If the reaction is zero order what happens if you change the concentration?
The rate is unaffected by changing the concentration of A
If the reaction is first order what happens when you change the concentration?
If the concentration is doubled, the rate also doubles
If the concentration increases by three then the rate also triples
If the reaction is second order what happens when you change the concentration?
If you double the concentration then the rate increases by 4 times (2 squared)
If you triple the concentration then the rate increases by 9 (3 squared)
What is the half life of a reactant?
The time taken for the concentration of the reactant to reduce by half
What happens to the reaction when the value of K increases?
The larger the value of K the faster the reaction
What effect does an increase in temperature have on the rate constant k?
Increase in temp
More energy in molecules
More frequent collisions
More molecules exceed the activation energy
Rate increases with temperature
which is shown by an increase in the rate constant
What is a reaction mechanism?
A series of steps that, together, make up the overall reaction
What is the rate-determining step?
The slowest step in the reaction mechanism of a multi-step reaction
Why is the overall rate affected by the rate-determining step?
A slow step becomes an obstacle to the whole process - reactants can become products only as fast as they can get through this slow step
The overall reaction can be no faster than the slowest step
What is an intermediate?
A species formed in one step of a multi-step reaction that is used up in a subsequent step, and is not seen as either a reactant or a product of the overall equation
When does a reaction reach equilibrium?
The rate of the forward reaction is the same as the rate of the reverse reaction
The concentrations of the reactants and the products remain the same
Reaction is in a close system
What is dynamic equilibrium?
Exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction
What is a homogeneous equilibrium?
An equilibrium in which all the species making up the reactants and products are in the same physical state
What is heterogeneous equilibrium?
An equilibrium in which species making up the reactants and products are in different physical states
What two things can you find from a balanced equation?
The reacting quantities needed to prepare a required quantity of product
The quantities of products formed by reacting together known quantities of reactants
What happens to the equation when Kc is larger than 1?
The reaction is product-favoured
The products on the right-hand side predominate at equilibrium
What does a Kc value of 1 mean?
Indicated the position of the equilibrium is halfway between reactants and products
What does a Kc value of less than 1 mean?
The reaction is reactant-favoured
The reactants on the left-hand side predominate at equilibrium
How does temperature affect Kc?
An increase in temp shifts the position of equilibrium in the endothermic direction
A decrease in temp shifts the position of the equilibrium into the exothermic direction
If the forward direction of a reaction is endothermic and the temperature increases, what happens to Kc?
It also increases
The equilibrium yield of the products on the right-hand side increases
The equilibrium yield of the reactants on the left-hand side decreases
When the forward reaction is exothermic and the temperature increases what happens to Kc?
Kc decreases
The equilibrium yield of the products on the right-hand side decreases
The equilibrium yield of the reactant on the left-hand side increases
How does changes in concentration affect the position of the equilibrium?
The equilibrium shifts to the side with the lowest concentration to alter the changes
How does pressure affect the position of the equilibrium?
If the pressure is doubled the concentrations of the gases will also double
The equilibrium shifts to restore the ratio back by favouring the side with the least gas moles
Does the presence of a catalyst affect pH?
Nope!
What does a large value for Kc mean?
The position of the equilibrium lies well to the right-hand side. In favour of the products
What happens to Kc if the forward reaction is endothermic?
Kc increases with an increase in temperature
What happens to Kc if the forward reaction is exothermic?
Kc decreases with an increase in temperature
What does a large value for K mean?
A fast rate of reaction
What is K?
The rate constant
When does K increase?
With an increase in temperature, so rate increases with increasing temperature
How do you measure K?
Experimentally
What is a Bronstead-Lowry acid?
A proton donor
What is a Bronstead-Lowry base?
A proton acceptor
What is an alkali?
A base that dissolves in water forming OH- ions
What is a Lewis acid?
An electron-pair acceptor
What is a Lewis base?
An electron-pair donor
What is neutralisation?
A chemical reaction in which an acid and a base react together to produce a salt and water
What is a monobasic acid and give an example of one
An acid which can release one proton
HCl
What is a dibasic acid and give an example of one
An acid which can release two protons
H2SO4
What is a tribasic acid and given an example of one
An acid which can release three protons
H3PO4
What three things do aqueous acids react with in typical acid-base reactions
Carbonates
Bases
Alkalis
What is the ionic equation for a neutralisation reaction including HCl, HNO3 and H2SO4?
H+ + OH- —> H2O
What is the ionic equation for a neutralisation reaction with carbonates? e.g. with CaCO3
2H+ + CaCO3 —> Ca2+ + CO2 + H2O
What is the ionic equation for the neutralisation reaction with bases? e.g. MgO
2H+ + MgO —> Mg2+ + H2O
What is the ionic equation for the neutralisation reaction with alkalis? e.g. KOH
H+ + OH- —> H2O
What is the ionic equation for the redox reaction of an acid and a metal? e.g. Mg
2H+ + Mg —> Mg2+ + H2
What is an acid-base pair?
A pair of two species that transform into each other by gain or loss of a proton
