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122 Cards in this Set
- Front
- Back
how does a catalyst speed up a chemical reaction? |
Alternative route (forms intermediate species) of lower activation energy |
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Characteristic property of transition metals that enables them to act as catalysts? |
Variable oxidation state |
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Suggest one reason why poisoning reduces the effectiveness of a heterogenous catalyst. |
Poison attaches to surface/blocks active site/reduces surface area |
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Suggest how poisoning of a catalyst can be minimised? |
Purify reactants/remove impurities |
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State why the electrode potential for standard hydrogen electrode is 0V |
By definition |
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Other than cost, why platinum electrodes are made by coating a porous ceramic material |
Increases the surface area (so reaction faster |
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Suggest why the emf of a fuel cell is the same in alkaline and acidic conditions. |
Same overall reaction |
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Other than lack of pollution, main advantage of fuel cell over rechargeable cell |
hydrogen and oxygen supplied continously/recharged quickly OR operated without stopping to recharge |
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Give one reason why fuel cell might not be carbon neutral. |
Hydrogen made using energy source that isnt carbon neutral |
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Explain why the bond enthalpy of a Cl-Cl bond is greater than Br-Br bond. |
Bonding pair closer to nucleus/bond is shorter/Cl is smaller atom; Attraction to bond pair is stronger |
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Why is the electron affinity of chlorine exothermic? |
Net attraction between chlorine nucleus and electron/Chloride ion is more stable |
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Explain the meaning of perfect ionic model? |
Ions are perfect spheres/point charges/no polarisation; only electrostatic attraction/no covalent interaction |
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Why is lattice enthalpy of silver chloride greater than silver bromide? Why is enthalpy of CaF2 > CaCl |
Chloride ion smaller; attracted more strongly flouride ion smaller; electrostatic attraction stronger/more energy to separate ions/ionic bonding stronger |
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Suggest why practical value of lattice enthalpy is greater than theoretical |
Covalent character; forces stronger than pure ionic bonding/stronger bonding/additional bonding |
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Explain why entropy increases with temp from 0? |
Particles VIBRATE more |
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Why is there a large entropy change during boiling? |
liquid to gas; big increase in disorder/much mroe random movement |
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State and explain one risk associated with cisplatin. |
kills or causes damage to normal cells/hair loss; may attach to DNA in normal cells |
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What shape is Co2+ in water? |
octahedral |
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Explain why ethanediamine complex is more stable than aqua complex |
entropy change is positive; 4 moles reactants form 7 moles products |
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Explain why chloride ion complex co-ordination number is diff to CoCl2 |
Chloride ion ligand too big to fit more than 4 |
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State and explain the trend in electronegativities across Period 3 from sodium to sulfur. (4) |
increases; increase in proton number; same number of electron shells/same radius/shielding of outer electrons remains the same; attraction of bond pair to nucleus increases |
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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 energy level; absorbs one colour of light from white light; Ti(IV) has no d electron so no electron transition with energy equal to that of visible light |
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2 reasons why a spectrometer is the most appropriate method for measuring conc of coloured ions in an experiment. |
Rapid determination of conc/easy to take many readings; does not interfere with reaction/does not use up reagent/can measure very low conc |
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Explain the shape of the autocatalysis curve |
Negative ions collide high activation energy; autocatalyst formed; MnO4- ions used up |
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Suggest what happens to the electrons in flourite when UV light is absorbed and when visible light is given out. |
UV absorbed: electrons move to higher energy levels/excited; visible out: fall back down/move to lower energy levels |
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What property of silicon dioxide can be deduced from teh fact that it reacts with NaOH not Hcl? |
Lewis acid |
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Suggest why ions from s block elements do not usually act as catalysts. |
only exist in one oxidation state |
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Why is the activation energy for S2O82- and I- high? |
both negative charge/repel each other |
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State how an element can be classified as a transition element. |
partially filled/incomplete d sub-shell/orbital |
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Explain the meaning of the term complex ion. |
Has ligand(s); linked by coordinate bonds |
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Explain why an aqueous solution of cobalt sulfate has a red colour |
Light is absorbed from incident white light; due to electrons moving to higher energy levels; remaining light transmitted is colour observed |
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Explain why CO is toxic |
bonds to the iron/haemoglobin/greater affinity for haemoglobin; displaces oxygen/prevents transport of oxygen |
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2 reasons why extraction of copper using scrap iron is environmentally friendly. |
Less CO2 released; less mining of copper ore; lower energy consumption |
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entropy and enthalpy are negative. explain why the reaction is not feasible at higher temp? |
G = H-TS; G>0; at high temp, -TS (is positive and greater than)H |
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One reason why methanol, synthesised from CO2 and hydrogen, may not be carbon-neutral |
CO2 produced during H2 manufacture |
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Describe a standard hydrogen electrode. |
H2 gas/bubbles; 1.0moldm^-3 HCl/H+; 298K and 100kPa; platinum |
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2H+(aq) + 2e- ----> H2(g) 0.00V Fe3+(aq) + e- -----> Fe2+ (aq) +0.77V suggest what happens when hydrogen gas is bubbled into a solution of Fe2+ and Fe3+ ions. |
Fe3+ reduced to Fe2+; E(Fe3+/Fe2+)> E(H+/H2) /Fe3+ better oxidising agent/cell emf 0.77V |
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Define the term enthalpy of lattice dissociation. |
Enthalpy change when 1 mole of a (solid) ionic compound/lattice is dissociated/separated into ions; ions in their gaseous state |
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Why is the first electron affinity of oxygen exothermic? |
Attractive force between the nucleus of an O atom and an external electron |
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Despite negative free energy change, why is a sample of magnesium oxide stable in air at room temp. |
Barrier of MgO/protective layer; or acitvation energy too high/rate too slow |
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For formation of MgO from magnesium and oxygen, why is entropy change negative |
1 mole of solid and 0.5 mole of gas reactants and 1 mole of solid products system becomes more ordered |
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Explain why enthalpy change is positive for melting of water. |
Hydrogen bonds between water molecules; energy required to break bonds |
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Freezing of water is exothermic. One reason why temp of water stays constant when freezing? |
Heat escapes |
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pH of NaOH? |
14 |
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pH of H3PO4? |
0 |
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2 reasons why platinum electrode? |
Inert; conducts electricity/allows electron flow |
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2 reasons why KNO3 is a suitable solution for salt bridge? |
Ions can move (conducts electricity/carries charge); does not react with solution in either electrode |
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State why it's possible to use a spectrometer to measure the conc of manganate ions in this reaction mixture. |
Manganate ions are coloured (purple) Other reactants and products not coloured |
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Give the meaning of the term autocatalyst and explain how the above curve indicates that the reaction is autocatalysed. |
Catalyst of the reeaction is a reaction product; starts off slow/gradient slower; gets faster/gradient steeper |
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2 other characteristic properties (aside from catalyst and compelex) and an example |
Variable oxidation state; Fe(II) and Fe(III); Coloured ions; Cu2+ (aq)/[Cu(H2O)6]2+ |
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Define Lewis base
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electron pair donor |
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An excess of dilute ammonia is added to aqueous iron(II) and left to stand for some time. State and explain observations |
Start with green solution; green ppt of Fe(H2O)4(OH)2; changes to brown solid; Iron(II) hydroxide oxidised by air to iron(III) hydroxide |
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Why is white phosphorous stored under water? |
Prevent it coming into contact/reacting with air/oxygen |
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Suggest why phosphorous(V) oxide is represented by P4O10 rather than P2O5. |
One molecule contains 4P and 10O/P4O10 is molecular formula |
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Explain why the use of an excess of NaOH to neturalise phosphoric acid solution might lead to environmental problems in the lake |
NaOH will make the lake alkaline/toxic/kill wildlife |
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Explain the meaning of the term electron affinity. |
Enthalpy change when one mole of gaseous atoms; form one mole of gaseous negative ions (with a single charge) |
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Explain why the electronegativity of flourine is greater than the electronegativity of chlorine. |
Flourine atom is smaller/shielding is less/outer electrons closer to nucleus; bonding pair of electrons more strongly attracted to nucleus |
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Explain why the hydraition enthalpy of the flouride ion is more negative than the hydration enthalpy of the chloride ion. |
Flouride ion is smaller/higher charge density; attracts water more strongly |
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Suggest why entropy change for dissolving AgF is positive. |
Increase in number of particles/more disorder |
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The free energy for the reaction to form NO from N2 and O2 stays constant at diff temp. why? |
no change in number of moles of gases; so entropy/disorder remains relatively constant/very small/S=0/TS=0 |
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One environmental advantage of rechargeable cell compared with non rechargeable cell |
metal compounds are re-used/supplies not depleted/cell not used; no landfill problems; less waste; less mining; less energy to extract metals |
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Suggest why ethanol is carbon-neutral |
CO2 released by combustion; taken up in photosynthesis |
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Suggest, in terms of electrons, why the colours of the complex ions [Cr(H2O)6]3+ and [Cr(H2O)5Cl]2+ are different. |
energy levels/gaps of the d electrons are different; diff wavelength/energy of light absorbed (when d electron excited) OR diff wavelength transmitted/reflected |
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Explain why [Cr(H2O)6]3+ behaves differently than [Cr(H2O)6]2+ when sodium carbonate is added |
Cr(III) is acidic and forms H+ ions; because it polarises water (more polarising power in book) |
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Co2+ is a catalyst for the reaction between sulfate(IV) ions with oxygen to form sulfate (VI) ions. Suggest why the reaction is faster in the presence of Co2+ ions |
Activation energy is lower; oppositely charged ions attract |
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Define bond dissociation enthalpy as applied to chlorine |
Enthalpy change to break the bond in 1 mole of chlorine molecules; to form two moles of gaseous chlorine atoms/free radicals Cl2(g) ---> 2Cl(g) |
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Explain why the enthalpy of atomisation of chlorine is exactly half the bond dissociation enthalpy of chlorine. |
Only one mole of chlorine atoms formed/half the amount of molecules involved |
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Explain why the enthalpy of formation of ClF3(g) is likely to be different from a data book value |
Cl-F bond is different in different compounds |
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Explain why magnesium ions attract water molecules. |
Water is polar/O in water has slightly negative charge. Magnesium ion/positive ion attracts O on a water molecule/attracts lone pairs NOT H BONDING |
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Explain why the evaporation of water is spontaneous even though this change is endothermic. |
Molecules become more disordered/more random when water changes from a liquid to a gas; positive entropy/entropy increases; TS>H G is negative |
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State the type of bonding in basic oxides. Explain why this type of bonding causes these oxides to have basic properties. |
Ionic; contains O2- ions; accept protons to form OH- |
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Why does sulfur dioxide form a weakly acidic solution? |
Reaction with water is equilbrium/lies far to the left/partially ionised/dissociated |
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Give one reason why impurities in the reactants can cause problems in processes that use heterogenous catalyst |
poison the catalyst/block the active sites/ adsorb onto the catalyst AND reduce surface area |
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Give the meaning of term heterogenous. |
In a different phase to the reactants |
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Explain the meaning of the term ligand and bidentate. |
Ligand is an electron pair donor; bidentate donates two electron pairs (to a transition metal ion) from different atoms/two atoms in the same molecule |
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Explain why CoCl4 and Co(H2O)6 have different colours |
D electrons/orbitals have different energies/d splitting is different; light energy is absorbed causing electrons to be excited; diff wavelength absorbed/reflected/transmitted |
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Explain the value for the enthalpy of hydration for the chloride ion is more negative than that for the bromide ion |
Chloride ions smaller; force of attraction between water and chloride ions stronger; chlroide ions attract slightly positive H/electron deificnet H on water |
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Explain why G for the dissolving of KCl is negative even though the enthalpy change is positive. |
Entropy change is positive/entropy increases; as 1 mol (solid) forms 2 moles aquous ions/number of particles increases/aqueous ions more disordered; TS>H |
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Explain in terms of molecules why the entropy is 0 when temp is 0K |
Molecules are stationary/not moving/not vibrating; no order/perfect order/max order |
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Explain why the magnitude of G decreases as T increases |
TS gets bigger/entropy change is positive |
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Outline a simple experiment to demostrate that MgO has ionic bonding |
Melt it; conducts electricity |
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Suggest why SiO2 is insoluble. |
Macromolecular; covalent bonding; water cannot supply enough energy to break the covalent bonds/hydration enthalpy |
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Explain why the melting point of phosphorous oxide is less than silicon dioxide |
Molecular with covalent bonding; weak vdW between molecules/little energy to break |
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Explain how the salt bridge provides an electrical connection between two electrodes. |
Has mobile ions |
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Electrochemical cell, 2 coppe electrodes, 1.0 moldm CuSO4(aq) on left, 0.2moldm CuSO4(aq) on right. Suggest why KCl is not a suitable salt bridge. Suggest why electrons move from right to left. Explain why current falls to 0 eventually. |
Cl- ions react with copper ions to form CuCl4; Cu2+ ions on left more conc; so reduction of copper ions favoured on left/left hand electrode positive; Copper ions at same conc in both electrodes |
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What factors affect the colour of a transition metal ion? |
Ligand; coordination number/shape; type of ion; oxidation state |
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Explain why a cobalt compound is able to act as a catalyst for 2CH3CHO + O2 ----> 2CH3COOH |
Has variable oxidation states; can act as an intermediate that lowers the activation energy |
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Explain in terms of the chelate effect, why the complex ion formed from cobalt and ethane-1,2-diamine is formed in preference to [Co(H2O)6]2+. |
Number of particles increases; so increase in diorder/entropy |
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Why does enthalpy change for electron affinity of flourine have a negative value? |
Attraction between the nucleus and the added electron; energy is released/product is more stable/lower energy/reaction is exothermic |
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Explain why the theoretical value for lattice enthalpy of AgF is different from experimental. |
Experimental lattice enthalpy allows for covalent interaction/distorted ions/polarisation OR AgF has covalent character; Theoretical assumes only ionic interaction/point charges/perfect spheres OR AgF not perfectly ionic |
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Define enthalpy of hydration. |
Enthalpy change when 1mole of a gaseous ion forms aqueous ions |
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Suggest why hydration of chlorine is exothermic. |
Water is polar has positive H; Cl- attracts the H in water |
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Describe what you would observe when magnesium is heated above 373K in absence of air with water. |
Brilliant white flame; white powder/solid/smoke |
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Explain why magnesium has a higher melting point than sodium. |
Magnesium has a higher charge/has more delocalised electrons/greater charge density; attracts delocalise/sea of electrons more strongly/stronger metallic bonding |
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Physical properties of macromolecular structures. |
High melting and boiling points; hard; brittle/not malleable; insoluble; non-conductor |
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One reason why cell is not recharged? |
Cell reaction cannot be reversed/zinc cannot be regenerated/danger of gas/oxygen/hydrogen produced; |
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How is an electric current generated? |
One electrode produces electrode; one accepts electrons |
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Explain why a fuel cell does not need to be recharged. |
Reagents continously supplied; concentration of reagents constant |
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Suggest advantage of using hydrogen in a fuel cell as opposed to in an internal combustion engine. |
More efficient/a greater prop of energy available converted into useful energy |
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Identify major hazard of fuel cell in an engine. |
hydrogen flammable/H+ and OH- corrosive/hydrogen explosive |
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Explain why complexes with different ligands are different colours. |
different energies of d electrons/different splitting of d electron energy levels/different energy gap of d electrons/different d orbital energies; different wavelength of light absorbed by electrons; different wavlength transmitted |
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Explain why the reaction of diaminoethane occurs with cobalt complex. |
increase in number of particles/4 particles form 7; increase in disorder/entropy; enthalpy change is small/no net change in bond enthalpies (same number and type of bonds broken and formed); G is negative |
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Suggest how the risk associated with cisplatin could be minimised. |
small amounts/short bursts/target the application/monitor the patient |
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One property of impurity in a sample that would cause the calculated mass of the sample (that reacted with dichromate) to be greater than the actual. |
Reducing agent/reacts with dichromate/not fully hydrated; for given mass impurity would react with more dichromate than similar mass of actual sample |
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Define enthalpy of atomisation. |
Enthalpy change for the formation of 1 mole of gaseous atoms; from the element in its standard state |
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Explain why entropy of nitrogen is much greater than carbon (graphite)? |
Nitrogen is a gas compared with solid carbon; nitrogen more disordered/random |
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State the type of reaction between sodium oxide and phosphorous oxide.
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Acid-base/neutralisation |
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Explain why the melting point of lithium oxide is greater than sodium oxide? |
Lithium ion is smaller/hsa higher charge dnesity; attracts oxide ion more strongly; |
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Suggest what is done to a heterogenous catalyst to maximise efficiency? |
SA increased; use of poweder/granules/finely divided/spreading out on mesh/support |
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Give the meaning of the term multidentate. |
Forms more than one co-ordinate bond/two or more |
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Give a reason why a vitamin with a cyanide ion as a ligand is not toxic. |
Ion strongly bound to transition metal by coordinate bond |
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Explain interactions between water and flouride ions during hydration. |
Water is polar/H is electron-deficient/; F ions attract water/H |
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Suggest why enthalpy change from mean bond enthalpies is different from practical? |
mean bond enthalpies taken over a range of diff compounds; differ from those in a single compound |
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Observation when sulfur reacts with oxygen? |
Blue flame; fumes/pungent/choking gas |
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Suggest why a thin layer of aluminium oxide prevents corrosion in moist air. |
Insoluble/imperable to air/water/oxide is inert |
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Why does X react with Y? |
Electrode potential more positive/greater than; so reduces/oxidises; as more power ful agent |
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One reason why a cell cannot be electrically recharged. |
Reaction not reversible |
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Give one reason why emf of lead acid cell changes over time. |
Reagents/ions used up/concentration decreases |
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Explain why voltage remains constant in a fuel cell. |
reagents/fuel supplied continously; conc of reagents remains constant. |
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Explain the meaning of the term complex. |
transition metal ion surrounded by one or more ligands; by coordinate bonds |
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What is E in the E=hv equation? |
Energy gained by hte excited electrons |
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Explain why iron(III) is more acidic than iron(II) |
Higher charge and greater charge density increases polarisation of coordinated water/weakens O-H bond |