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Chemistry > Rates, Equilibrium and pH > Flashcards

Rates, Equilibrium and pH Flashcards

0
Q

Initial rate of reaction

A

The change in concentration of a reactant or product per unit time at the start of a reaction, when t=0

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1
Q

Rate of reaction

A

The change in concentration of a reactant or product per unit time

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2
Q

Rate equation

A

A + B -> C is given by k[A]^m [B]^n

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3
Q

The order with respect to a reactant is…

A

The power to which the concentration is raised in the rate equation

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4
Q

The overall order of a reaction is…

A

The sum of the individual orders

m+n

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5
Q

The rate constant, k, is…

A

The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation

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6
Q

Half life of a reactant

A

The time taken for the concentration of the reactant to reduce by half

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7
Q

A reaction mechanism is…

A

A series of steps that, together, make up the overall reaction

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8
Q

What is the rate determining step?

A

The slowest step in the reaction mechanism of a multi-step reaction

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9
Q

What is an intermediate?

A

A species formed in one step of a multi step reaction that is used up in a subsequent step, and is not seen as either a reactant or product of the overall equation

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10
Q

The equilibrium law states…

A

aA + bB cC + dD

Kc = ([C]^c [D]^d) / ([A]^a [B]^b)

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11
Q

Define dynamic equilibrium

A

A dynamic equilibrium exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction

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12
Q

What is a homogeneous equilibrium?

A

An equilibrium in which all the species making up the reactants and products are in the same physical state

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13
Q

What is a heterogeneous equilibrium?

A

An equilibrium in which species making up the reactants and products are in different physical states

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14
Q

When does Kc change?

A

Kc only changes with temperature

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15
Q

What is a Brønsted-Lowry acid?

A

A proton donor

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16
Q

What is a Brønsted-Lowry base?

A

A proton acceptor

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17
Q

Define neutralisation.

A

Neutralisation is a chemical reaction in which an acid and a base react together to produce a salt and water

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18
Q

Acid + metal –>

A

Salt + Hydrogen

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19
Q

What is a conjugate acid-base pair?

A

A pair of two species that transform each other by gain or loss of a proton

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20
Q

pH =

A

-log [H+(aq)]

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21
Q

[H+(aq)] =

A

10^-pH

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22
Q

Le Chateliers principle

A

When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to minimise the change

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23
Q

What is an alkali?

A

A base that dissolves in water forming OH-

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24
Q

Conjugate base

A

The species left after an acid donates a proton

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25
Q

Conjugate acid

A

The species produced when a base accepts a proton

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26
Q

Acid dissociation constant, Ka

A

[H+][A-] / [HA]

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27
Q

pKa

A

-log Ka

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28
Q

Ionic product of water

A

[H+][OH-]

at 25 degrees, this is 1x10^-14

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29
Q

Buffer solution

A

A mixture that minimises pH changes on addition of small amounts of acid or base

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30
Q

Equivalence point

A

The point in a titration where the volume of one solution has reacted exactly with the volume of the second solution

31
Q

End point

A

The point in a titration where there are equal concentrations of the weak acid and conjugate base forms of the indicator

32
Q

Standard enthalpy change of neutralisation

A

The energy that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H2O under standard conditions

33
Q

The half-life of a first-order reaction is _____________ of concentration

A

Independant

34
Q

Kc =

A

PRODUCTS
___________
REACTANTS

35
Q

What is the effect on Kc if temperature is raised in an exothermic reaction?

A

Decrease

36
Q

What is the effect of Kc if temperature is raised in an endothermic reaction?

A

Kc increases

37
Q

How is Kc affected by changes in pressure, concentration, or the presence of a catalyst?

A

It is not affected

38
Q

What is the difference between a strong and weak acid?

A

A strong acid completely dissociates in solution, whereas a weak acid only partially dissociates

39
Q

What does Ka show?

A

The extent of acid dissociation

40
Q

Large Ka =

A

Large extent of dissociation - strong acid

41
Q

A high value of Ka means a ______ value of pKa

A

Low

42
Q

The smaller the pKa the stronger/weaker the acid

A

Stronger

43
Q

[H+] (strong monobasic acid)

A

[HA]

44
Q

[H+] (weak monobasic acid)

A

Sqrt (Ka x [HA])

45
Q

[H+] (strong base)

A

Kw / OH-

46
Q

HCOOH H+ + COO-

Ka=

A

[H+][COO-] / [HCOOH]

47
Q

The stronger the acid the _________ the value of Ka and the _______ the value of pKa

A

GREATER

SMALLER

48
Q

How can one make a buffer solution?

A

A weak base and the salt of a weak acid

49
Q

Lattice enthalpy

A

The enthalpy change that accompanies the formation mole of ionic compound from its gaseous ions under standard conditions

50
Q

Explain the three trends in lattice enthalpy

A

-ve enthalpy change

More exothermic if ionic charge increases (increased CHARGE DENSITY on the ions - stronger attraction)

More exothermic if ionic radius decreases (Charge density increases as radius decreases - increased attraction)

51
Q

Change in enthalpy of solution =

A

Enthalpy of hydration - lattice enthalpy

52
Q

Enthalpy change of solution

A

The enthalpy change when one mole of a compound is completely dissolved in water under standard conditions

53
Q

Enthalpy change of hydration

A

The enthalpy change of 1 mole of gaseous ions is dissolved in water to form 1 mole of aqueous ions under standard conditions

54
Q

What factors determine the magnitude of lattice enthalpy?

A

Ionic radius and charge

55
Q

Explain why the lattice enthalpies of magnesium oxid and sodium chloride are different

A

The charge/radius ratios of Mg2+ and O2- ions are far greater than for Na+ and Cl- ions, so the attractive forces between the Mg2+ and O2- ions will be greater

56
Q

What is a catalyst?

A

A substance that increases the rate of reaction by providing an alternative route for the reaction with a lower activation energy.

The catalyst is chemically unchanged at the end of the reaction

57
Q

What effect, if any, does adding a catalyst have on activation energy?

A

Reduces activation energy

58
Q

What effect, if any, does increasing temperature have on activation energy?

A

No effect

59
Q

What effect, if any, does increasing the concentration of a reactant have on activation energy?

A

No effect

60
Q

What happens to the rate of reaction as time elapses?

A

Rate decreases with time

61
Q

Explain what happens to the rate of reaction as time elapses, using the idea of particles

A

As time elapses, the concentration of the reactant decreases, and so there will be fewer reacting particles per unit volume.

Hence, fewer successful collisions will take place, resulting in a lower rate of reaction

62
Q

How is the rate of reaction at a particular time, t, determined from a graph.

A

A tangent is drawn to the curve at time t, and the negative gradient is measured

63
Q

In a Boltzmann distribution graph, what is measured on each axis?

A

Number of particles with a particular energy on the y-axis, energy of the particles on the x-axis

64
Q

Explain how an increase in temperature increases the rate of a chemical reaction

A

As the temperature increases, the kinetic energy of the reactant molecules also increases.

There will be a greater proportion of molecules exceeding the activation energy and more effective collisions will result.

65
Q

What is the equation that shows the second electron affinity for oxygen?

A

O- (g) + e- —> O2-

66
Q

What is the equation that shows the third ionisation energy for sodium?

A

Na2+ (g) —> Na3+ (g) + e-

67
Q

What is the equation that shows the standard enthalpy of formation for magnesium carbonate?

A

Mg(s) + C(s) + 3/2O2 (g) —> MgCO3(s)

68
Q

Explain why the enthalpy of neutralisation for any strong acid and strong base is always equal to or near to -57kJ mol^-1

A

Irrespective of the acid or base being used, the ionic equation will always be:

H+ + O- —> H2O

Since the other ions will act as spectators and not be involved

69
Q

Why are enthalpies of hydration always exothermic?

A

Because gaseous ions are being hydrated (surrounded by water molecules) and the resulting bond formation evolves heat

70
Q

Explain how, upon addition of acid or base, a buffer solution minimises pH change

A

HAH+ + A-

On addition of alkali:

reacts with [HA]
moves equilibrium to right
H+ + OH- —-> H20

On addition of acid:

reacts with [A-] reducing excess H+ ions
moves equilibirum to left

71
Q

If extra acid is produced in the blood, how do buffers prevent the pH from falling?

A

An increase in H+ (aq) ions in the blood is removed by HCO3-, forming carbonic acid

The carbonic acid is converted into aqueous carbon dioxide by an enzyme.

The dissolved carbon dioxide is converted into CO2 gas in the lungs, which is then exhaled

72
Q

How does temperature affect rate of reaction?

A

+10K = rate x 2

73
Q

For an endothermic reaction, an increase in temperature causes:

A

Increase in K, equilibrium shift to the right, and more product

74
Q

How do you find OH- from pH?

A

Kw / -log (pH)

Chemistry (7 decks)

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