5.1 Rates, equilibrium and pH Flashcards
What is ‘rate of reaction’?
the speed at which a chemical reaction takes place
What does order mean?
the power to which a concentration of a reactant is raised in the rate equation
What is a rate constant?
the rate constant, k, is a proportionality constant that links the rate of reaction with the concentration of reactants
What is the definition of half-life?
the time taken for the concentration of a reactant to reduce by half
What is the rate-determining step?
the slowest step of the reaction, that determines the rate of the whole reaction
What are the units for rate of reaction
mol dm-3 s-1
How do you calculate rate constant, k?
k = ln(2) / t1/2 (half life(s))
Describe a zero order rate-concentration graph
straight horizontal line
y-intercept gives rate constant, k
changes in conc have no effect on rate
Describe a first order rate-concentration graph
straight line through origin
rate directly proportional to conc
rate constant is gradient
Describe a second order rate-concentration graph
upward curve with increasing gradient - from origin
2nd graph of rate-(conc)^2 drawn to find rate constant - gradient of 2nd line
Describe a zero order concentration-time graph
straight line with negative gradient
reaction rate doesnt change
gradient=k
half life decreases
Describe a first order concentration-time graph
downwards curve - decreasing gradient
half life is constant - time for reactant to half each time
Describe a second order concentration-time graph
downwards curve, steeper at start
half life increases with time
How does an increase in temperature affect the rate of reaction and rate constant?
rate increases - boltzsman distribution shifts to the right so more particles overcome Ea
- particles move faster and collide more frequently
What is the definition of mole fraction?
a measure of how much of a given substance is present in a reaction mixture
What is the equation for mole fraction?
xA = number of moles of substance A / total number of moles
What is the definition of partial pressure?
the pressure an individual gaseous substance would exert if it occupied a whole reaction vessel on its own
What is the equation for partial pressure?
mole fraction * total pressure
Which methods can determine concentrations at equilibrium?
titrations
using a colorimeter
How to determine concentrations at equilibrium using a titration?
How to determine concentrations at equilibrium using a colorimeter?
What is the effect of an increase temperature on Kc
exothermic - Kc decreases
endothermic - Kc increases
Does pressure affect Kc?
No
What happens to Kc if the concentrations increase?
Kc stays the same as the concentrations will change to restore the original Kc
What is the effect of a catalyst on a reaction?
increases rate of forwards and backwards reaction by the same amount
lowers activation energy
reaction can take place at a lower temperature
cheaper
What is the effect of increasing pressure on Kc?
increased pressure = increases concentrations
so Kc will stay the same as concentrations will change to revert Kc to original
What is a Bronston-Lowry acid?
an acid that donates a proton
What is a Bronston-Lowry base?
a base that accepts a proton
What is the equation to work out pH?
pH = -log [H+]
What is the equation that calculates [H+]?
[H+] = 10^ (-pH)
What is a conjugate acid-base pair?
a set of 2 species that change into one another by gaining or losing a H+ ion
they have a difference of 1 H+ ion
What is a mono-basic acid? (give an example)
acid that releases 1 H+ proton
e.g. HCl
What is a di-basic acid? (give an example)
acid that releases 2H+ protons
e.g. H2SO4
What is a tri-basic acid? (give an example)
acid that releases 3 H+ protons
e.g. H3PO4
What type of acid is CH3COOH ?
monobasic acid - the cooh group only counts
acid + carbonate
salt + carbon dioxide + water
acid + base
salt + water
acid + alkali
salt + water
(redox)
acid + metal
salt + hydrogen
What does the acid dissociation constant, Ka show?
the actual extent of acid dissociation measured by an equilibrium constant
What is Ka for
HA(aq) —— H+ (aq) + A- (aq)
Ka = [A-][H+] / [HA]
What does a large Ka value show?
a large extent of dissociation - a strong acid
What does a small Ka value indicate?
small extent of dissociation - a weak acid
What is the equation to find pKa and Ka?
pKa = -log10(Ka)
Ka = 10^(-pKa)
What does a large and small pKa value show?
small pKa value - stronger acid
high pKa value - weaker acid
What does a low pH value show?
a high concentration of H+
What does a high pH value show?
a low concentration of H+ ions
