F325 - Rates, Equilibrium and pH Flashcards
What is the order of a reaction?
The power to which the concentration of a reactant is raised in the rate equation.
What is meant by the term rate of reaction?
The amount in moles of a reactant which is used up or product which is formed in a given time.
What does a zero order of reaction indicate?
The reactant does not affect the rate.
What does a first order of reaction indicate?
The reactant concentration is directly proportional to the rate.
What does a second order of reaction indicate?
The square of the reactant concentration is directly proportional to the rate.
What is meant by the term rate constant?
The proportionality constant, k, in a rate equation. Rate = k[A][B]
What is the rate determining step?
The slowest step in a reaction mechanism.
What is meant by the term half-life?
The time taken for the concentration of a reactant to fall to half its original value.
For a first order reaction what is independent of the concentration?
Half-life
What is needed for the experimental determination of the rate equation using the initial rates method?
Separate experiments using different concentrations of one of the reactants. The time is measured and then:
rate = concentration/time
What affects the rate constant of a reaction?
Temperature
Why does pressure not affect the rate constant?
It changes the concentrations of the reactants. (Change in volume!)
How does increasing the temperature affect the rate constant?
Increases k
What does the rate equation tell you about a multi-step reaction mechanism?
The species and the number of them which take place in the rate determining step.
How is the overall order of a reaction determined?
The sum of the orders with respect to the individual reactants.
What is Le Chatelier’s principle?
When any conditions affecting the position if equilibrium are changed, then the position of equilibrium will shift to minimise that change.
How will changing the concentration affect the position of equilibrium?
Increase concentration: shift to the side where the increase did not take place
Decrease concentration: shift to the side where the decrease did take place
How will changing the pressure affect the position of equilibrium?
Increase pressure: shift to the side with the fewer number of moles (of gas)
Decrease pressure: shift to the side with more moles (of gas)
How will changing the temperature affect the position of equilibrium?
Increase temperature: shift in the direction of the endothermic reaction
Decrease temperature: shift in the direction of the exothermic reaction
How is Kc calculated?
Kc = [RHS or products]/[LHS or reactants]
How does increasing the temperature affect the value of Kc?
Endothermic reaction: Kc increases
Exothermic reaction: Kc decreases
What factors do not affect the value of Kc?
- Concentration
- pressure
- catalysts
Larger Kc values would indicate what about a reaction?
High theoretical yields
What is a meant by Brønsted-Lowry acid?
A species which can donate a proton.
What is meant by a Brønsted-Lowry base?
A species which can accept a proton.
What does the term amphoteric mean?
A substance which can behave as an acid or a base, depending on the conditions.
What is meant by the term conjugate acid-base pair?
The acid in the forward reaction and the base in the reverse reaction are a pair (or vice versa).
What is a strong acid?
A proton donor which fully dissociates.
What is a weak acid?
A proton donor which only partially dissociates.
What does the acid dissociation constant show and how is it calculated?
The extent of acid dissociation.
Ka = [H+][A-]/[HA]
How is pKa calculated?
pKa= -logKa
How is pH calculated?
pH= -log[H+]
How is hydrogen ion concentration calculated given the pH of a solution?
[H+] = 10^-pH
What is the ionic product of water?
Kw = [H+][OH-] = 1.00 x 10^-14 (constant)
What are the two assumptions made to simplify the Ka calculation?
- Assume that [H+] = [A-]
- Assume that [HA] is approx equal to the concentration of the acid (only a very small number of molecules have dissociated)
What is meant by the term buffer solution?
A system that minimises pH changes on addition of small amounts of an acid or base.
What is needed to make a buffer solution?
A weak acid and a salt of the weak acid.
What are the products formed between a weak acid and a base?
Salt (of the weak acid) and water
In an acidic buffer solution what happens on the addition of a small amount of acid?
H+ ions react with salt ions and shift equilibrium to the left (produces more of the weak acid).
In an acidic buffer solution what happens on the addition of a small amount of alkali?
OH- ions react with the weak acid and shift the equilibrium to the right (producing more hydrogen ions).
How is the buffer ratio calculated?
Ka/[A-] = [H+]/[HA]
How does the carbonic acid-hydrogencarbonate buffer work in blood pH levels?
- haemoglobin reacts with oxygen
- oxygen released in tissues so aerobic respiration can take place
- carbon dioxide and water produced
- they are in equilibrium which forms hydrogen ions
- hydrogencarbonate ion reacts with hydrogen ions to produce more carbon dioxide
- carbons dioxide carried back to lungs and breathed out
What needs to be considered when drawing an acid-base titration pH curve?
- strength/pH of starting solution
- are concentrations of acid and base equal (this means it’ll be one to one and use the same volume!)
- where does the vertical section go (volume + make sure it is vertical)
- strength/pH of added solution
How is a suitable indicator chosen?
The end point or pH range of the indicator is in the vertical section of the pH curve or is within the equivalence point of the titration.
What is the enthalpy change of neutralisation?
Enthalpy change to produce one mole of water from the reaction of an acid and an alkali
What is the relationship between pH and pOH?
pH + pOH = 14
