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60 Cards in this Set
- Front
- Back
What is the enthalpy change? |
Heat change in a reaction under constant pressure |
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Explain why ammonium chloride dissolves spontaneously in water even though the process is endothermic (2) |
Increase in disorder (entropy change is positive) G < 0 (TS>H) |
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Although a reaction is feasible at 2300K, it does not occur to a significant extent until temp reaches 3300K. Why? (1) |
Reaction too slow Activation energy too high |
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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 |
No reaction zinc(II) reduction more negative than iron(II) reduction/cell voltage -0.32 |
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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 |
electrode potential of Fe3+ more positive than Cr2+ |
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Observations of [Cr(H2O)]3+ and formula of product with: XS NaOH Na2CO3(aq) |
green solution [Cr(OH)3]3- green ppt. bubbles/fizzing/effervescence Cr(H2O)3(OH)3 |
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Give the meaning of the term electronegativity (2) |
Ability of an attom to attracto electrons towards itself from within a covalent bond (bonding pair of e-) |
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State and explain the trend in electronegativity across period 3 from Na to Cl. (3) |
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 |
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Explain how the type of bonding in P4O10 can be predicted by a consideration of electronegativity. (1) |
electronegativity diff small/simiilar |
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Explain why the ester methyl ethanoate has a lower boiling point than propanoic acid. (2) |
H bonding in propanoic acid stronger than intermolecular forces in ester |
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Suggest why a polyester melts at a higher temp than polyethene. (2) |
dipole dipole forces stronger than vdW/require more energy to overcome |
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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. |
MnO4- + 8H+ + 4Mn2+ ----> 5Mn3+ + 4H2O 2Mn3+ + C2O42- ---> 2Mn2+ + 2CO2 |
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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) |
[Co(NH3)6]2+ formed easier to oxidise H2O2 (or air or oxygen) |
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State why EDTA4- can act as a multidentate ligand. Explain why the EDTA4- ion readily displaces unidentate ligands such as water. |
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; |
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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 |
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 |
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Define the term lattice enthalpy of dissociation (2) |
Enthalpy change when 1mol of a solid ionic lattice is dissociated into its ions; forms gaseous ions; (under standard conditions) |
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Explain the meaning of the term perfect ionic model. (1) |
Ions are perfect spheres; ions are point charges; no polarisation; no covalent character/only electrostatic attraction; |
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State 2 properties of ions that influence the value of a lattice enthalpy calculated using perfect ionic model. |
IONIC radius (not atomic); ionic charge |
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Predict whether magnitude of lattice enthalpy of dissociation from practical cal will be greater or less than that of perfect |
Greater covalent interaction Equal AgCl is perfectly ionic/no covalent character |
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Explain why the enthalpy of hydration for chloride ions is more negative than that for bromide ions |
Chloride ion is smaller/higher charge density attracts water more strongly attracts electron deficient hydrogen |
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Explain why the free-energy change for the dissolving of KCl in water is negative even though the enthalpy change is positive (3) |
Entropy change is positive/increase in disorder; because 2mol of product for 1mol of reactant; TS>H (G<0) |
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Explain why the entropy is 0 when temp is 0K (2) |
Particles not moving/vibrating/have no energy; no disorder; |
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Explain why entropy increases with temp. (2) |
As T increases, particles move/have more energy Disorder increases |
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Explain why entropy change with boiling is greater than that with melting (2) |
Bigger change in disorder |
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Outline a simple experiment to demonstrate magnesium has ionic bonding. (2) |
Melt it Molten conducts electricity |
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Suggest why SiO2 is insoluble in water (3) |
Macromolecular; covalent bonding; watter cannot break covalent bonds (hydration enthapy |
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Explain why the melting point of phosphorous oxide is lower than SiO2 (2) |
Simple molecular with COVALENT bonding weak vdW forces |
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Explain how the salt bridge provides an electrical connection between two electrodes (1) |
Mobile ions/completes circuit (and don't react) |
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Suggest why KCl is not suitable for a salt bridge(1) |
Chloride ions would react with X |
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Explain why the current in a concentration cell falls to 0 (1) |
Same conc in both electrode |
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Explain why an electron transition causes a solution with a transition metal ion to be coloured. |
Particular wavelength light absorbed; remaining wavelength transmitted |
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State 3 features of transition complexes that results in a diff colour. |
Shape/co-ordination number species of ligand oxidation state/charge type of metal |
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Explain why a cobalt compound is able to act as a catalyst (2) |
Variable oxidation state alternative route with lower activation energy (transfer electrons between compounds) |
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Explain why magnesium ions attract water molecules (2) |
Water is polar; Attracted to Mg2+ |
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Explain why the evaporation of water is spontaneous even though this change is endothermic (4) |
Increase in disorder positive entropy change TS> H G<0 |
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Explain why sodium oxide has a high melting point (2) |
Ionic LATTICE; strong electrostatic attraction between oppositely charged ions |
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Explain why ionic bonding = basic properties. (2) |
negative ion (specific ion); accepts protons |
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What conditions should standard hydrogen electron be operated at? |
298K H2 at 100kPa H+ at 1moldm^-3 no current |
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Define: bronsted lowry base nucleophile lewis base |
proton acceptor electron pair donor electron PAIR donor |
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Suggest why the free-energy change is equal to 0 when a liquid boils. |
Change is spontaneous/feasible water and water vapour are at equilibrium |
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Explain why the enthalpy of vaporisation for liquid HF is greater than that for liquid NH3 (3) |
Both have hydrogen bonding H-F more polar (F is more electronegative than N) Stronger hydrogen bonds |
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Give one reason why the e.m.f of the MnO2(oxidising agent) Zn(reducing agent) cell decreases after use |
Zn used up |
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2 reasons why something can be regarded as a catalyst |
alternative route not used up (chemically changed)(is regenerated) speeds up reaction lowers activation energy |
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What is a heterogenous catalyst? |
One that is in a different phase to reactants |
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Give one reason why silver is a poor heterogenous catalyst? |
Reactants adsorb poorly |
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State how a catalyst speeds up a chemical reaction (2) |
Alternative reaction pathway (intermediate species) of lower activation energy |
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Suggest why posioning reduces the effectiveness of a heterogenous catalyst |
Poison attaches to surface/decreases surface area |
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One reason why platinum electrodes are made by coating a porous material. |
Increase SA increase rate |
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Why is the emf of a hydrogen-oxygen fuel cell in acidic conditions the same as one in alkaline conditions? |
Overall reaction is the same |
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Advantage of a fuel cell over re-chargeable |
refuelled quickly no need to stop and recharge |
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Why are hydrogen-oxygen fuel cells not carbon neutral? |
Hydrogen made using non carbon-neutral source |
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Explain why the bond enthalpy of Cl-Cl bond is greater than that of Br-Br bond. (2) |
Cl is a smaller atom with fewer electron shells so bonding pair is closer to nucleus Shared pair held more tightly/stronger attraction |
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Suggest why the electron affinity of chlorine is an exothermic change. |
net attraction between chlorine nucleus and electron/chloride ion more stable |
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Why is lattice dissociation of AgCl greater in practice than theoretical calc? (2) |
AgCl has covalent character/covalent interaction forces are stronger than ionic attraction/additional bonding |
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State and explain one risk associated with the use of cisplatin (2) |
Attach to DNA in normal cells kills/damages healthy cells (hair loss) |
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Explain why co-ordination number of [CoCl4]2- is different from species in CoCl2. |
chloride ion ligand too big to fit more than 4 around cobalt ion |
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Explain why sodium and phosphorous have diff melting points. Also explain the link between electronegativity and type of bonding. (6) |
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 |
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Explain why Ti(III) compounds are usually coloured but Ti(IV) compounds are colourless. |
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 |
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2 reasons for use of spectrometer. |
Can take many readings/rapid determination of concentration does not affect/react with sample and can use v small conc |
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(curve with conc of manganate ions in manganate and ethanedioate reaction) Explain the shape of the curve. |
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 |