5.1 RATES,EQUILIBRIUM & PH Flashcards
Define rate of reaction
- Change in concentration of a reactant or product per unit time
Define order
- The power to which the concentration of a reactant is raised to in the rate equation
What does rate constant, K link?
- Links rate of reaction with concentration of reactions raised to their orders
State the rate equation
Define overall order
- The sum of the individual orders in the rate equation
Define half life (of a reactant)
- the time taken for the concentration of a reactant to reduce by half
Define rate-determining step
- the slowest step of a multi-step reaction that determines the rate at which the overall reaction proceeds
What is meant by a reactant in zero order?
- The rate is unaffected by changing concentration of that reactant
What is meant by a reactant in first order?
- The rate is directly proportional to the concentration of that reactant
What is meant by a reactant in second order?
- The rate is equal to the change in concentration squared of that reactant
State which reactant order does NOT appear in the rate equation
- Zero order reactants
Draw all the orders on a concentration-time graph
Draw all the orders on a rate-concentration graph
State how the rate of reaction would be determined from a concentration-time graph that produces a curved line of best fit
- A tangent to the curve at given point
- Find the gradient using Δconc/time taken (=Δy/Δx)
Define half-life
- The time taken for the concentration of a reactant to reduce by half
State and explain which type of rate graph we identify the half life for
- Concentration-time graphs of FIRST ORDER reactants
- Because the half life is independant of concentrations so each half life is the same length
State the equation that links half-life with rate constant K
State how to work out initial rate from a concentration-time graph
- Draw a tangent at t=0 and work out the gradient (Δy/Δx)
State the relationship between reactants in the rate-determining step and the reactants in the rate equation
- Only and all of the reactants that appear in the rate equation must be in the rate-determining (slow) step
(im unsure if this is right, look at ur notes, hivi)
State the arrhenius equation
State what the arrhenius equation links
- Links activation energy and temperature to the rate constant K
State the reason for use of a colourimeter
- Monitors visual colour changes
Define continuos monitoring
- Taking measurements of rates at specific intervals to measure the change in quantity of a substance
Explain the effect of temperature of the rate constant and hence, the rate of reaction
- As temperature increases, more KE given to particles
- Thus, more frequent successful collisions with sufficient energy to exceed activation energy
- This increases the value of the rate constant and therefore also the rate of reaction
State how we get rid of the exponential eˣ in the arrhenius equation
- We natural log (ln) BOTH sides of the equation
State which two parts of the arrhenius equation we can be asked to determine graphically AND state the new rearranged arrhenius equation we would use
1) Activation energy Ea
2) Arrhenius constant A
State the arrhenius equation after it has been natural logged (ln)
Define homogenous equilibrium
- Equilibrium where all species making up reactants and products are in the same physical state
Define heterogenous equilibrium
- Equilibrium where the species making up reactants and products are in the different physical states
State what we do if we need to determine a Kₚ or Kc expression for a heterogenous equilibrium
- NEVER include solid and liquid species
- (Only gaseous and aqueous)
State what the ICE table stands for and which questions we use it in
Initial moles, Change in moles, Equilibrium moles
- Use in any type of equilibrium questions
State the Kc expression
Define partial pressure
- The pressure an individual gaseous substance would exert if it occupied the whole reaction vessel alone
Define total pressure
- The sum of all individual pressures (partial pressures)
Define mole fraction
- The proportion of a given substance present in a reaction mixture
State the formula for partial pressure
State the formula for total pressure
State the formula for mole fractions
State the Kₚ expression
State what a value of 1 for Kc or Kp would indicate
- That equilibrium lies in the middle
State what a value greater than 1 for Kc or Kp would indicate
- That equilibrium lies toward the right/products/forward
State what a value less than 1 for Kc or Kp would indicate
- That equilibrium lies toward the left/reactants/backward
Define a bronsted-lowry acid
- A proton donor species
Define a bronsted-lowry base
- A proton acceptor species
Define monobasic, dibasic and tribasic acids
- Monobasic acid means each molecule releases one proton (e.g HCl)
- Dibasic acid means each molecule releases two protons (e.g H₂SO₄)
- Tribasic acid means each molecule releases three protons (e.g H₃PO₄)
Define conjugate acid-base pair
- A set of two species that turn into each other by the gain or loss of a proton
What does the acid dissociation constant, Ka measure?
- The actual extent of acid dissociation
State the Kₐ expression then simplify it.
State the two expressions that convert between Kₐ and pKₐ
State what a large Kₐ value indicates
- A large Kₐ value means a large extent of acid dissociation
- The acid is strong
State what a small Kₐ value indicates
- A small Kₐ value means a small extent of acid dissociation
- The acid is weak
State what a high/low pKₐ value indicates
- High pKₐ means a weaker acid
- Low pKₐ means a stronger acid
State the two expressions that convert between pH and [H⁺]
State what a pH change of 1 would increase [H⁺] by
- A pH change of 1 increases the [H⁺] by 10 times
Define strong acid and draw an equation
- An acid that fully dissociates in aqueous solution to release H+ ions
Define weak acid and draw an equation
- An acid that partially dissociates in aqueous solution to release H+ ions
State the assumption made for strong monobasic acids
We assume:
[H⁺] = [HA]
State the two assumptions made for weak monobasic acids
We assume:
1) [H⁺] = [A⁻]
2) [HA] undissaociated = [HA] equilibrium
State the Ka expression for a strong monobasic acid
State the Ka expression for a weak monobasic acid
State the equation to find [H⁺] of a weak acid
Explain the limitation of assumption used for weak acids
- We assume that:
[HA] undissaociated = [HA] equilibrium - However for “stronger” weak acids that dissociate more than 5% we cannot use the assumption above
- This is because “stronger” weak acids would have a higher Ka value than we calcuated, we are underassuming
State the reaction for ionisation of water and state where equilibrium lies
- Equilibrium lies well to the left
State what the ionic product of water Kᵥᵥ expression determines
- The relative concentrations of H+ and OH- of an aqueous solution
State the Kᵥᵥ expression
State the assumption made for pure water
We assume:
[H⁺]=[OH⁻]
Define alkali
- A water soluble base that dissociates to release OH- ions in solution
State three strong alkalis
1) NaOH
2) KOH
3) Ca(OH)₂
State a weak alkali
NH₃
State the assumption we make for strong monobasic alkalis
We assume:
[OH⁻]=[NaOH]
State the equation to find [H⁺] of a strong monobasic alkali
Define buffer solution
- A mixture that minimised pH changes on small additions of acids or bases
State what a buffer solution is made of
- A weak acid, HA
- Its conjugate base, A⁻
State the three ways of making a buffer solution
1) A solution of weak acid + a solution of its salt
2) A solution of weak acid + its solid salt
3) An EXCESS solution of weak acid + an alkali (partial neutralisation)
State the reaction for a buffer mixture and state their relative proportions
Describe the dissociation of salts thus, state the assumption we make
- Salts fully dissociate into its cations and its anions when in water
We assume:
[Salt]=[A⁻]
State the equation to determine the [H⁺] of a buffer solution
Explain the effect of adding acid to a buffer solution
(CONJUGATE BASE REMOVES ADDED H⁺)
- [H⁺] increases
- The conjugate base A⁻ reacts with the added H⁺ ions, to form more acid HA
- Equilibrium shifts to the left, removing the added H⁺ ions
Explain the effect of adding alkali to a buffer solution
(CONJUGATE BASE REMOVES ADDED H⁺)
- [OH⁻] increases
- The small concentration of H⁺ reacts with the added OH⁻ ions, to form more water molecules
- HA dissociates to restore the lost H⁺
- Equilibrium shifts to the right, removing the added OH⁻ ions
Explain the role of the carbonic acid-hydrogen carbonate buffer solution
- Healthy blood pasma is 7.35 to 7.45
- carbonic acid-hydrogen carbonate buffer solution controlls blood pH
- hydrogencarbonate ions can remove acidic stuff released into the blood by converting into carbonic acid
- Enzymes then convert this to aqueous carbon dioxide then into gasesous carbon dioxide which is then exhaled in the lungs
Define equivalence point
- The point where the volume of one solution has reacted exactly with the volume of the second solution
Explain how to calibrate a pH probe
- Rinse the probe in deionised water
- Blott dry and place into solution of known pH
- Leave it to read and ensure it reads the correct pH
- Repeat with pH 4/7/10
State what an indicator is and how it works
- An indicator is just a weak acid (HIn)
- It has one colour as a weak acid and another colour as a conjugate base
Define endpoint
- When there are equal concentrations of weak acid and conjugate base
- The colour of the endpoint is midway of the indicators two colours
[HIn] = [In⁻]
State how to pick a suitible indicator
- the end point of the indicator needs to have a pH value as close as possible to the equivilence point pH value of the titration
Draw out the four types of titration curves
Explain why no indicator is suitible for a weak acid-weak base titration
- Because there literally is no equivalence point
Do catalysts increase concentrations of reactants/products
- NO catalysts have no effect on equilibrium concentration
- (They only increase rate of attainment of equilibrium)
Do catalysts increase the Kc value
- NO catalysts have no effect on equilibrium concentrations
- (They only increase rate of attainment of equilibrium)
State the formula to determine pre-exponential factor A from lnA
