Chem5 Random Q's

Front 1

What is the enthalpy change?

Back 1

Heat change in a reaction under constant pressure

Front 2

Explain why ammonium chloride dissolves spontaneously in water even though the process is endothermic (2)

Back 2

Increase in disorder (entropy change is positive)

G < 0 (TS>H)

Front 3

Although a reaction is feasible at 2300K, it does not occur to a significant extent until temp reaches 3300K. Why? (1)

Back 3

Reaction too slow

Activation energy too high

Front 4

Fe2+ + 2e- ---> Fe(s) -0.44V

Zn2+ + 2e- ---> Zn(s) -0.76V

Predict the products, if any, when iron metal reacts with aqueous zinc(II) ions and use electrode potentials to explain your answer

Back 4

No reaction

zinc(II) reduction more negative than iron(II) reduction/cell voltage -0.32

Front 5

Fe3+ + 2e- ---> Fe2+ +0.77V

Cr2+ + 2e- ---> Cr(s) -0.91V

Predict the products, if any, when aqueous iron(III) reacts with aqueous chromium(II) ions and use electrode potentials to explain your answer

Back 5

electrode potential of Fe3+ more positive than Cr2+

Front 6

Observations of [Cr(H2O)]3+ and formula of product with:

XS NaOH

Na2CO3(aq)

Back 6

green solution

[Cr(OH)3]3-

green ppt.

bubbles/fizzing/effervescence

Cr(H2O)3(OH)3

Front 7

Give the meaning of the term electronegativity (2)

Back 7

Ability of an attom to attracto electrons towards itself

from within a covalent bond

(bonding pair of e-)

Front 8

State and explain the trend in electronegativity across period 3 from Na to Cl. (3)

Back 8

Increases;

More protons or greater nuclear charge;

similar shielding/electrons in same shell/same number of electron shells/smaller atomic radius;

Attraction of bond pair to nucleus increases

Front 9

Explain how the type of bonding in P4O10 can be predicted by a consideration of electronegativity. (1)

Back 9

electronegativity diff small/simiilar

Front 10

Explain why the ester methyl ethanoate has a lower boiling point than propanoic acid. (2)

Back 10

H bonding in propanoic acid

stronger than intermolecular forces in ester

Front 11

Suggest why a polyester melts at a higher temp than polyethene. (2)

Back 11

dipole dipole forces

stronger than vdW/require more energy to overcome

Front 12

Write 2 equations to show how the transition metal catalyst reacts and is reformed:

oxidation of ethanedioate ions by acidified potassium manganate(VII), autocatalysed by Mn2+ (aq) ions.

Back 12

MnO4- + 8H+ + 4Mn2+ ----> 5Mn3+ + 4H2O

2Mn3+ + C2O42- ---> 2Mn2+ + 2CO2

Front 13

Cobalt(II) ions cannot easily be oxidised to cobalt(III) ions in water. Suggest why this can be carried out in aqueous ammonia and identify a suitable oxidising agent (3)

Back 13

[Co(NH3)6]2+ formed

easier to oxidise

H2O2 (or air or oxygen)

Front 14

State why EDTA4- can act as a multidentate ligand.

Explain why the EDTA4- ion readily displaces unidentate ligands such as water.

Back 14

EDTA 4- has 6 lone pairs to donate (can form 6 co-ordinate bonds);

number of species increases from 2 to 7;

increase in disorder/positive entropy change;

enthalpy change is small;

hence negative free energy change/more stable ion (complex) is formed;

Front 15

Describe what you would observe for the following reactions:

KBr + KI with chlorine water

BaCl2 and MgCl2 using dilute sulphuric acid

CoCl2 and CuCl2 using conc HCl

Back 15

KBr -- orange/brown solution

KI --- brown solution/black solid (NOT purple gas)

BaCl2 --- white ppt

MgCl2 -- no change

CoCl2 -- goes blue

CuCl2 -- goes yellow-green

Front 16

Define the term lattice enthalpy of dissociation (2)

Back 16

Enthalpy change when 1mol of a solid ionic lattice is dissociated into its ions;

forms gaseous ions;

(under standard conditions)

Front 17

Explain the meaning of the term perfect ionic model. (1)

Back 17

Ions are perfect spheres;

ions are point charges;

no polarisation;

no covalent character/only electrostatic attraction;

Front 18

State 2 properties of ions that influence the value of a lattice enthalpy calculated using perfect ionic model.

Back 18

IONIC radius (not atomic);

ionic charge

Front 19

Predict whether magnitude of lattice enthalpy of dissociation from practical cal will be greater or less than that of perfect

Back 19

Greater

covalent interaction

Equal

AgCl is perfectly ionic/no covalent character

Front 20

Explain why the enthalpy of hydration for chloride ions is more negative than that for bromide ions

Back 20

Chloride ion is smaller/higher charge density

attracts water more strongly

attracts electron deficient hydrogen

Front 21

Explain why the free-energy change for the dissolving of KCl in water is negative even though the enthalpy change is positive (3)

Back 21

Entropy change is positive/increase in disorder;

because 2mol of product for 1mol of reactant;

TS>H (G<0)

Front 22

Explain why the entropy is 0 when temp is 0K (2)

Back 22

Particles not moving/vibrating/have no energy;

no disorder;

Front 23

Explain why entropy increases with temp. (2)

Back 23

As T increases, particles move/have more energy

Disorder increases

Front 24

Explain why entropy change with boiling is greater than that with melting (2)

Back 24

Bigger change in disorder

Front 25

Outline a simple experiment to demonstrate magnesium has ionic bonding. (2)

Back 25

Melt it

Molten conducts electricity

Front 26

Suggest why SiO2 is insoluble in water (3)

Back 26

Macromolecular;

covalent bonding;

watter cannot break covalent bonds (hydration enthapy

Front 27

Explain why the melting point of phosphorous oxide is lower than SiO2 (2)

Back 27

Simple molecular with COVALENT bonding

weak vdW forces

Front 28

Explain how the salt bridge provides an electrical connection between two electrodes (1)

Back 28

Mobile ions/completes circuit

(and don't react)

Front 29

Suggest why KCl is not suitable for a salt bridge(1)

Back 29

Chloride ions would react with X

Front 30

Explain why the current in a concentration cell falls to 0 (1)

Back 30

Same conc in both electrode

Front 31

Explain why an electron transition causes a solution with a transition metal ion to be coloured.

Back 31

Particular wavelength light absorbed;

remaining wavelength transmitted

Front 32

State 3 features of transition complexes that results in a diff colour.

Back 32

Shape/co-ordination number

species of ligand

oxidation state/charge

type of metal

Front 33

Explain why a cobalt compound is able to act as a catalyst (2)

Back 33

Variable oxidation state

alternative route with lower activation energy

(transfer electrons between compounds)

Front 34

Explain why magnesium ions attract water molecules (2)

Back 34

Water is polar;

Attracted to Mg2+

Front 35

Explain why the evaporation of water is spontaneous even though this change is endothermic (4)

Back 35

Increase in disorder

positive entropy change

TS> H

G<0

Front 36

Explain why sodium oxide has a high melting point (2)

Back 36

Ionic LATTICE;

strong electrostatic attraction between oppositely charged ions

Front 37

Explain why ionic bonding = basic properties. (2)

Back 37

negative ion (specific ion);

accepts protons

Front 38

What conditions should standard hydrogen electron be operated at?

Back 38

298K

H2 at 100kPa

H+ at 1moldm^-3

no current

Front 39

Define:

bronsted lowry base

nucleophile

lewis base

Back 39

proton acceptor

electron pair donor

electron PAIR donor

Front 40

Suggest why the free-energy change is equal to 0 when a liquid boils.

Back 40

Change is spontaneous/feasible

water and water vapour are at equilibrium

Front 41

Explain why the enthalpy of vaporisation for liquid HF is greater than that for liquid NH3 (3)

Back 41

Both have hydrogen bonding

H-F more polar (F is more electronegative than N)

Stronger hydrogen bonds

Front 42

Give one reason why the e.m.f of the MnO2(oxidising agent) Zn(reducing agent) cell decreases after use

Back 42

Zn used up

Front 43

2 reasons why something can be regarded as a catalyst

Back 43

alternative route

not used up (chemically changed)(is regenerated)

speeds up reaction

lowers activation energy

Front 44

What is a heterogenous catalyst?

Back 44

One that is in a different phase to reactants

Front 45

Give one reason why silver is a poor heterogenous catalyst?

Back 45

Reactants adsorb poorly

Front 46

State how a catalyst speeds up a chemical reaction (2)

Back 46

Alternative reaction pathway (intermediate species)

of lower activation energy

Front 47

Suggest why posioning reduces the effectiveness of a heterogenous catalyst

Back 47

Poison attaches to surface/decreases surface area

Front 48

One reason why platinum electrodes are made by coating a porous material.

Back 48

Increase SA increase rate

Front 49

Why is the emf of a hydrogen-oxygen fuel cell in acidic conditions the same as one in alkaline conditions?

Back 49

Overall reaction is the same

Front 50

Advantage of a fuel cell over re-chargeable

Back 50

refuelled quickly

no need to stop and recharge

Front 51

Why are hydrogen-oxygen fuel cells not carbon neutral?

Back 51

Hydrogen made using non carbon-neutral source

Front 52

Explain why the bond enthalpy of Cl-Cl bond is greater than that of Br-Br bond. (2)

Back 52

Cl is a smaller atom with fewer electron shells so bonding pair is closer to nucleus

Shared pair held more tightly/stronger attraction

Front 53

Suggest why the electron affinity of chlorine is an exothermic change.

Back 53

net attraction between chlorine nucleus and electron/chloride ion more stable

Front 54

Why is lattice dissociation of AgCl greater in practice than theoretical calc? (2)

Back 54

AgCl has covalent character/covalent interaction

forces are stronger than ionic attraction/additional bonding

Front 55

State and explain one risk associated with the use of cisplatin (2)

Back 55

Attach to DNA in normal cells

kills/damages healthy cells (hair loss)

Front 56

Explain why co-ordination number of [CoCl4]2- is different from species in CoCl2.

Back 56

chloride ion ligand too big to fit more than 4 around cobalt ion

Front 57

Explain why sodium and phosphorous have diff melting points. Also explain the link between electronegativity and type of bonding. (6)

Back 57

Big difference in electronegativity = ionic bonding;

sodium oxide is ionic lattice;

strong attraction between ions;

phosphorous oxide is simple molecular with covalent bonding;

weak vdW between molecules

Front 58

Explain why Ti(III) compounds are usually coloured but Ti(IV) compounds are colourless.

Back 58

Ti(III) has a d electron that can be excited to a higher level

one wavelength of light absorbed

Ti(IV) has no d electrons so no electron transition with energy equal to that of white light

Front 59

2 reasons for use of spectrometer.

Back 59

Can take many readings/rapid determination of concentration

does not affect/react with sample and can use v small conc

Front 60

(curve with conc of manganate ions in manganate and ethanedioate reaction) Explain the shape of the curve.

Back 60

Intially slow rate

no catalyst and negative ions repel each other, activation energy is high for them to collide

Increases

as catalyst is formed (Mn2+)

Decreases

As manganate ions are used up