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A-level Chemistry > A2 Physical > Flashcards

A2 Physical Flashcards

Thermodynamics, Kinetics, Equilibrium, Electrode Potentials, Acids Bases and Buffers

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1
Q

State Hess’s Law

A

At constant temperature, enthalpy changes accompanying a chemical reaction will remain constant, irrespective of the way the reactants react to form product

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2
Q

Two properties that determine lattice enthalpy

A

Small ions, large charges

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3
Q

Two things Born-Haber cycles used for

A

Determining which compounds are most likely to be formed
Calculating enthalpy changes that cannot easily be determined experimentally for ionic lattices

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4
Q

What are the 5 steps for a Born-Haber Cycle

A

Atomisation of metal
Atomisation of non-metal
First IE of metal
First electron affinity of non-metal
Enthalpy of lattice formation

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5
Q

What are the three steps to determining the enthalpy of solution

A

Enthalpy of lattice dissociation
Hydration of cations
Hydration of anions

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6
Q

What is responsible for the discrepancy between experimental values and theoretical values of lattice enthalpy

A

Polarisation, small highly charged cation pulls the electrons away from the large highly charged anion

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7
Q

What are the three factors that affect the possibility of a reaction occuring

A

Enthalpy, entropy, temperature

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8
Q

Define rate of reaction

A

Change in concentration of any reactant per unit time

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9
Q

What species are in the rate equation

A

Any that occur in a reaction before and including the rate determining step, including catalysts

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10
Q

Why does the rate constant not increase directly proportional to temperature?

A

Temperature affects both the frequency of collisions and the collisions that have enough energy to collide sufficiently and react

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11
Q

State the Arrhenius equation

A

K=Ae^-Ea/RT

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12
Q

What is “A” in the Arrhenius equation

A

The pre-exponential factor

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13
Q

What are the units for A

A

The same as the units for K

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14
Q

Define partial pressure

A

The pressure that would be exerted by one of the gases in the mixture if it occupied that same volume on its own

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15
Q

For a reaction, aA+bB ⇌ yY+zZ, give the Kp expression

A

Kp=pY^y(pZ^z)/pA^a(pB^b)

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16
Q

Which direction do electrons flow in a cell

A

Most reactive metal to least reactive metal

17
Q

What is used to complete the circuit for a cell

A

Salt bridge

18
Q

What is the name given to a table of EΘ values that allows the theoretical voltage of a cell to be calculated

A

Electrochemical series

19
Q

What is used to measure the standard voltage produced by a metal

A

Standard hydrogen electrode

20
Q

What is the IUPAC standard representation of a salt bridge

A

|| Two solid lines

21
Q

What is the formula for calculating the EMF for a cell using the electrochemical series

A

EMF= EΘpositive electrode - EΘ negative electrode

22
Q

How can electrochemical series and cells be used to determine the feasibility of a reaction

A

The voltage according to the electrochemical series allows the direction of electron flow to be worked out. This means that electrons will flow in that direction but they will not flow positive to negative

23
Q

Explain how a zinc carbon cell works

A

A carbon inert electrode is in the centre of a manganese oxide and powdered carbon mixture, within a paste of NH4Cl and water surrounded by a Zn case. Zn becomes Zn2+ ions and NH4+ become NH3 to produce a current

23
Q

Explain how Lead-acid batteries work

A

Lead is oxidised, Lead oxide is reduced. This is reversible, so is recharged by the cars generator.

24
Q

Give the name of the cell that is rechargeable and a standard size

A

nickel-cadmium

25
Q

Give the name of the cell that is rechargeable, light and does not leak so is used in laptops and smartphones

A

Lithium ion

26
Q

Explain the benefits of a hydrogen fuel cell

A

Only product is water so clean
Lower temperature than combustion of hydrogen so no nitrous oxides produced
No reactive metals used to make them

27
Q

Give the bronsted-lowry definition of an acid and a base

A

Acid - proton donor, base - proton acceptor

28
Q

Give the equation for calculating pH

A

pH=-log10[H+]

29
Q

Give the equation for the Kw expression

A

Kw=[OH-][H+]

30
Q

Give the equation for pKa

A

pKa=-log10Ka

31
Q

Describe the shape of a titration curve for a strong acid and a weak base

A

Begins ≈ pH2, s-shaped curve, flattens at 8-10 pH

32
Q

Explain the importance of the half neutralisation point

A

Half of the acid has reacted, so [HA]=[A-], so pKa=pH

Also useful for buffers

33
Q

What are two ways that acidic buffers can be made

A

Weak acid
½ neutralisation buffer

34
Q

Give two examples of basic buffers (including the chemicals)

A

NH4Cl- and NH3 mixture
H+ +HCO3- → CO2 +H2O (in blood)

35
Q

Give two everyday uses of buffers

A

Shampoo, detergents

A-level Chemistry (6 decks)

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