Physical Chemistry and Transition Element Flashcards by rachel belsey

write the method of writing half equations
and use the example of VO(2+) –> VO2 (+)

Calculate oxidation states on each side
VO (2+) = +4
VO2(+) = +5
Balance element changing oxidation state (already balanced)
Sort out electrons. if the oxidation state becomes more -tive then gains elec, more +ve loses elec
VO(2+) –> VO2(+) + e- (V becomes 1 more positive so one elec lost)
Sort out Oxygens, for every O gained/ lot add/remove one H2O molecule
Sort out Hs. for every H gained/lost, add/remove 1 H+ ion
check if the total elec charge on the left equals right then YAY

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write the half equation for Pb (4+) –> Pb (2+)

Pb (4+) + 2e(-) – Pb (2+)

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write the half equation for SO4 (2-) –> H2S

SO4 (2-) + 8e(-) + 10H(+) –> H2S + 4H2O

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write the half equation for this reaction
SO2 + 2H2) + 2Cu(2+) + 2Cl- –> SO4(2-) + 4H+ + 2CuCl

SO2 + 2H2O + 2Cu(2+) + 2Cl(-) –> SO4(2-) + 4H+ + 2CuCl

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write the half equation for the reduction of MnO4(-) ions to Mn(2+)

MnO4 + 8H+ + 5e- –Mn(2+) + 4H2O

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how do you calculate the amount of iron in an iron tablet from a potassium manganate titration

n(MnO4-) = C x V / 1000 = ans
ans x 5 = n(Fe)2+
M = n x Mr –> M(Fe) per tablet

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what is a zero order reactant

the reactant has no effect on the rate
is not shown in the rate equation

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what is a first order reactant

when the rate depends on the reactant’s concentration raised to the power of 1
so if the concentration of reactant is doubled, rate is also doubled

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what is a second order reactant

when the rate is dependent on the reactant’s concentration raised to the power of 2
so if the concentration of the reactant is doubled, the rate increases by a factor of 2^2 = 4

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what is the rate equation

rate = k [A]ᵐ [B]ⁿ

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what does each symbol in the rate equation stand for

rate = rate of reaction
k = rate constant
[A] = concentration of A
ᵐ = order of reaction with respect to A
[B] = concentration of B
ⁿ = order of reaction with respect to B

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what is K in the rate equation

the proportionality constant that mathematically converts between the rate of reaction and concentration of orders

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what is the overall order

sum of orders with respect for each reactant
rate = k [A]ᵐ [B]ⁿ
overall order = ᵐ + ⁿ

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when can you use concentration-time graphs

when you take continuous measurements throughout the course of the reactants

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what is the shape of a concentration-time graph for a zero order reaction

produces a straight line with a negative gradient
value of the gradient is equal to the rate constant k

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what is the shape of a concentration-time graph for a first order reaction

downward curve with a decreasing gradient over time
time for concentration of reactant to halve is constant = half life which can be determined from this graph

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what is shape of a concentration time graph for a second order reaction

a steeper downward curve that tails off more slowly

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what is a half life

the time taken for half a reactant to be used up

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what is the pattern linked to exponential decay

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when, in first order reactions, have a constant half life with the concentration halving every half life

how do you determine k from a concentration time graph

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k = ln2/ t₁/₂

what is K when t₁/₂ = 100

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1n2/ 100 = 0.693/100
6.93 x 10⁻³ s⁻¹

what is k when t₁/₂ = 46

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0.0151 s⁻¹

when can you plot a concentration-rate graph

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form measurements of rate of reaction at different concentration

what is the shape of rate-concentration graph for a zero order reactant

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produces a horizontal straight line with zero gradient
rate = k[A]⁰
intercept on y axis = k
reaction rate doesn’t change with increasing concentration

what is the shape of rate-concentration graph for a first order reactant

straight line graph through the origin rate = k[A]¹ rate is directly proportion to concentration for a first order relationship the rate constant can be determined by measuring the gradient of the straight line of this graph

what is the shape of the rate-concentration graph for a second order reactant

produces an upward curved with an increasing gradient rate = k [A]² rate constant cannot be obtained directly from the graph

how can you obtain the rate constant from a rate-concentration graph of a second order reactant

by plotting a second graph of the rate against the concentration² which results in a straight line through the origin gradient of the straight line graph = k

CH3COOH(l) + CH3OH(l) ⇌ CH3COOCH3(l) + H2O(l) Explain why the student uses a large excess of methanol in this experiment.

to keep the concentration of CH₃COOH constant zero order with respect to CH₃OH to ensure that equilibrium is far to the right

how can you show on a concentration-time graph that a reaction is first order with respect to [A]

show 2 half lives calculated and that the half-lives remain constant

In step 1, ethanal reacts with OH− ions to set up an acid–base equilibrium. In step 2, compound A is formed. complete the equilibrium constant CH₃CHO + OH− ⇌ ---- + ----

−CH2CHO + H2O

similar reaction takes place when propanone, (CH3)2CO, is mixed with OH−(aq) ions. Draw the structure of the organic product of this reaction.

CH₃CHOHCH₂CHO

2H2O2(aq) → 2H2O(l) + O2(g) A student investigates the decomposition of H2O2(aq) by measuring the volume of oxygen gas produced over time. All gas volumes are measured at room temperature and pressure. he student uses 25.0 cm3 of 2.30 mol dm−3 H2O2. From the results, the student determines the concentration of H2O2(aq) at each time. The student then plots a concentration–time graph. Suggest a different experimental method that would allow the rate of this reaction to be followed over time

measure mass loss

Explain how the student could determine the activation energy, Ea, for the reaction graphically using values of k and T.

plot graph using k and 1/T measure gradient Ea = –8.314 × gradient

A student investigates the rate of reaction between iodine, I2, and propanone, CH3COCH3, in the presence of H+ ions. Explain why absorbance decreases during the experiment.

iodine solution has a yellow colour concentration of I₂ decreases

what are the steps that make up an overall reaction

reaction mechanism

what is the rate determining step

the slowest step in the reaction mechanism

what does the rate equation contain when considering the rate determining step

only the reacting species involved in the rate determining step

how can you tell that the reaction mechanism is correct

rate equation includes reacting species involved in rate-determining steps the orders in rate equation match the number of species involved in rate-determining step

identify the intermediate and 2-step mechanism for this reaction (CH₃)₃CBr + OH⁻ --> (CH₃)₃COH + Br⁻ rate = k [(CH₃)₃CBr]

OH⁻ has no effect on the rate ∴ included in the fast step (CH₃)₃CBr --> =slow + OH⁻ --> = fast so overall (CH₃)₃CBr + OH⁻ --> (CH₃)₃COH + Br⁻ step 1 must form both species - 1 = other product Br⁻ and other = (CH₃)₃C⁺ step 1: (CH₃)₃CBr --> (CH₃)₃C⁺ + Br⁻ SLOW step 2:(CH₃)₃C⁺ + OH⁻ --> (CH₃)₃COH + Br⁻

what are the factors affecting rate constant and how

temperature shifts the Boltzmann to the right, increasing the proportion of particles that exceed Eₐ as temp increases, particles move faster and collide more frequently

what is the Arrhenius equation

K = Ae^ ⁽⁻ᴱᵃ/ᴿᵀ⁾ the exponential relationship between k and temperature

what does each symbol stand for in Arrhenius equation

K = Ae⁽⁻ᴱᵃ/ᴿᵀ⁾ k = rate constant A = frequency factor e⁽⁻ᴱᵃ/ᴿᵀ⁾ = linked to activation energy and temp T = temperature in kelvin R = gas constant / 8.314 Jmol⁻¹K⁻¹

what does e⁽⁻ᴱᵃ/ᴿᵀ⁾ represent

represents the proportion of molecules that exceed Eₐ and that have sufficient energy for a reaction to take place

what does A take into account in Arrhenius

the frequency of collisions with the correction orientation slightly increases with temperature as frequency increases but is essentially constant gives the rate if there were no activation energy

what is the logarithmic form of Arrhenius

ln (k) = - Eₐ / RT + ln (A) ln(k) = -Eₐ/ R x 1/T + ln(A)

how can you plot the logarithmic form of Arrheniu

ln(k) = -Eₐ/ R x 1/T + ln(A) y = m x + c

what does a plot on ln k against 1/T produce

gives a downward straight line the gradient m of

Physical Chemistry and Transition Element Flashcards

(47 cards)