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Chemistry > 5.1 > Flashcards

5.1 Flashcards

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1
Q

What is the rate of reaction?

A

The rate at which products are formed.
Rate of reaction = Δ [products or reactants] / time

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2
Q

What is the order and overall order of a reaction?

A

The order defines the power of the relationship to which the concentration of a reactant affects the rate of the reaction.
The overall order is the sum of all the orders.

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3
Q

What is the half-life and how can it be used to identify the order of a reaction?

A

The time it takes for the concentration of a reactant to halve.
The half-life is constant for a first order reaction. This can be used to differentiate between first and second order reactants’ concentration-time graphs. Zero order reactants have a constant gradient.

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4
Q

What is the rate determining step?

A

The slowest step in a multistage reaction.

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5
Q

What is the rate equation?

A

rate = k [A]^m [B]^n, where solids are not considered

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6
Q

How is the half-life calculated?

A

k = ln2 / half-life

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7
Q

What conclusions can be drawn from rate-concentration graphs?

A

If the graph shows a completely horizontal line (so one where the rate is unaffected by the concentration) the reactant is zeroth order.
If the graph has a constant gradient going through (0,0) (so the rate is directly proportional to the concentration) the reactant is first order.
If the graph shows a curve going through (0,0) (so the rate is disproportionally affected by the concentration) the reactant is second order.

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8
Q

How can k be found from a rate-concentration graph?

A

k is the gradient of rate-concentration graphs but only for first order reactions.

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9
Q

What are the techniques and procedures used to investigate reaction rates?

A

Initial rates method and continuous monitoring (colour, mass loss ect.)
change the initial conditions and see how this affects the initial rate.

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10
Q

What does the rate equation show?

A

The stoicheometrty lof the rate determining step.
When suggesting possible mechanisms, always have the first step producing one of the overall products.

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11
Q

What factors affect the rate constant?

A

Temperature. Higher temperatures increase the rate constant.

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12
Q

What is the mole fraction?

A

moles of gas A / total moles of all gases

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13
Q

What is partial pressure?

A

Partial Pressure is the pressure each gas would exert if it occupied the entire vessel on its own at the same temperature.

Partial pressure of A = mole fraction x total pressure

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14
Q

What are the expressions for Kc and Kp?

A

Kc = [A]^m / [B]^n
Kc does not consider solids and is only affected by temperature.
Kp = p^m (A) / p^n (B)
Kp only considers gases and is only affected by temperature.

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15
Q

What conditions affect the equilibrium constants?

A

Temperature. Higher temperatures increase the rate constant. For all other conditions the equilibrium position will shift in the direction which opposes the change and restore the value of Kc/Kp

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16
Q

What are acids and bases?

A

Acids are proton donors .
Bases are proton acceptors.

17
Q

What are monobasic, dibasic, and tribasic acids?

A

Monobasic: HCl, HNO3
Dibasic: H2SO4
Tribasic: H3PO4

18
Q

What is a conjugate acid-base pair?

A

HCl + H2O —-> H3O+ + Cl-
acid 1 base 1
base 2 acid 2

19
Q

What is there to know about Ka?

A

HA <-> H+ + A-
Ka = [H+][A-] / [HA]

Since Ka can be so large we use the logarithmic scale given by: pKa =-logKa.
The smaller the value of pKa, the stronger the acid.

20
Q

What is the relationship between [H+] and pH?

A

pH = - Log([H+])
For strong mono basic acids which completely deionise in water [H+] = [Acid]
For weak acids which partially dissociate, Ka may need to be used: Ka = [H+]^2 / [HA]
For these approximations: the extent of disassociation is so small that [HA]&raquo_space; [H+], any water present will have disassociated by such a small amount that it will not affect the concentration of [H+] so [H+] = [A-], and [HA] - [H+] = [HA].

21
Q

What is Kw?

A

Water can act as both an acid (-> H+ + OH-) and a base (H+ -> H3O+).
Water exists in equilibrium: H2O <-> H+ + OH-
This is known as the ionisation of water. The equilibrium lies well to the left.
Kw = Kc x [H2O] = [H+][OH-] where [H+]=[OH-]
Kw is called the ionic product of water.
At 25°C Kw = 1 x 10^-14 mol^2dm^-6.

The pH of a strong base can be calculated by knowing that [H+] = Kw / [OH-]
where [OH-] = [strong monobasic alkali].

22
Q

What are buffer solutions?

A

A buffer solution minimises pH changes on addition of small amounts of an acid or base.

A buffer solution is made from:
(1) (CH3COOH/NaOH)
A weak acid and a strong alkali.
(2) (CH3COOH/CH3COONa)
A weak acid and a salt of a weak acid. The weak acid partially dissociates whilst the salt of the weak acid salt completely dissociates so: HA <-> H+ + A-

On addition of an acid: [H+] is increased, the conjugate base, A-, reaches with the H+ ions and the equilibrium shifts to the left, removing most of the added H+ ions.

On addition of an alkali, [OH-] is increased, the small concentration of H+ ions react with the OH- ions producing water, so HA dissociates, shifting the equilibrium to the right to restore the reacted H+ ions.

For a type (2) buffer: Ka = [H+][A-] / [[HA] where [HA] equilibrium = [HA] undissociated and [A-] = [salt].

23
Q

What is an example of a buffer system?

A

The carbonic acid–hydrogencarbonate buffer system which keeps the blood between a pH of 7.35-7.45.

The weak acid is carbonic acid, H2CO3.
The conjugate base is HCO3-
SO, H2CO3 <-> H+ + HCO3-

Most materials released into the blood are acidic so are converted into H2CO3 which can be turned into aqueous CO2 with an enzyme which can then be converted into a gas and exhaled in the lungs.

24
Q

What is the equivalence point?

A

The point at which the acid has exactly reacted with the alkali.
The centre of the vertical section of the titration curve.

25
Q

How do indicators work?

A

Indicators are often represented as HIn where they undergo: HIn <-> H+ + I-
When there are equal amounts of weak acid and conjugate base, the indicator has reached it’s end point.

26
Q

How is a pH probe calibrated?

A

The probe is rinsed with water.
It is then blotted dry.
It is then placed in solutions of known pH to ensure that it is accurate.

27
Q

[titration curve diagrams needed]

A

Chemistry (17 decks)

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