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| Frage | Antworten |
| Define Rate of reaction | the change in concentration of a reactant or product per unit time |
| How do you find rate of reaction from a concentration vs time graph? | Measure gradient |
| what is initial rate of reaction | the change in concentration of a reactant or product per unit time at t = 0 |
| name some ways of monitoring reaction rates | PH changes, changes in volume/pressure, loss of mass, formation of a precipitate |
| What does zero order mean? | The rate is unaffected by change in concentration of reactant |
| What does first order mean? | The rate is directly proportional to concentration of reactant |
| What does second order mean? | The rate is proportional to the concentration of reactant squared |
| Define the rate constant | The constant that links the rate of reaction with the concentrations of reactants |
| How do you work out overall order? | Sum of individual orders |
| Define half life | The time taken for concentration of the reactant to reduce by half |
| If a reactant has a constant half life which order must it be? | First |
| how does half live vary for a second order reactant? | It increases with time |
| How does half life vary for a zero order reactant? | It decreases with time |
| Describe the shape of a rate/conc graph for a zero order reactant | Straight horizontal line |
| Describe the shape of a rate/conc graph for a first order reactant | Straight line through origin with gradient 1 |
| Describe the shape of a graph of rate/conc for a second order reactant | Line through origin of increasing gradient (similar to y=x^2) |
| How does temperature affect K? | Increasing temperature increases K ( a larger K gives a faster rate of reaction) |
| Define reaction mechanism | A series of steps that together make up the overall reaction |
| Define rate-determining step | The slowest step in reaction mechanism of a multi step reaction |
| How do you know which compounds are involved in rate determining step from rate equation? | All compounds in the rate equation are involved...the number of which is equal to their power |
| Define intermediate | A species formed in one step of a multi step reaction that is used up in a subsequent step and is not seen as a reactant or product of the overall equation |
| Define dynamic equilibrium | A closed system when the rate of the forward reaction is equal to the rate of the reverse reaction |
| what is the equilibrium law? | Kc= (C^cxD^d)/(A^axB^b) |
| Define homogenous equilibrium | An equilibrium where all the species making up the reactants and products are in the same physical state |
| Define heterogeneous equilibrium | An equilibrium where the species making up the reactants and products are in different physical states |
| Do you use concentrations or moles in Kc calculations? | Concentrations |
| What does a Kc bigger than 1 represent? | the reaction is product favoured |
| How is Kc affected by temperature? | if forward reaction is endothermic Kc will increase, if forward reaction is exothermic Kc will decrease with increasing temperature |
| Define a Bronsted-Lowry acid | proton donor |
| define a Bronsted-Lowry base | Proton acceptor |
| define an alkali | A base that dissolves in water forming OH- ions |
| Define a monobasic, dibasic and tribasic acid | Monobasic - releases 1 proton into solution Dibasic - releases 2 protons into solution Tribasic - releases 3 protons into solution |
| Complete general equation: Acid +metal = | a salt and hydrogen |
| Complete general equation: Acid + base = | a salt and water |
| Complete general equation: acid + metal carbonate = | a salt, carbon dioxide and water |
| Define an acid-base pair | A set of two species that transform into each other by gain or loss of a proton |
| define PH | PH= -log(H+(aq)) |
| How do you convert from PH to conc of Hydrogen ions? | 10^(-PH) |
| Define a strong acid | An acid that completely dissociates in solution |
| Define a weak acid | An acid that partially dissociates in solution |
| Define acid dissociation constant | Ka = (H+xA-)/(HA) |
| What do high values of pKa mean about strength of acids | Weaker acid |
| For a known concentration of a strong acid what does the concentration of H+ ions equal? | Same as conc of acid |
| For weak acids what does ka expression simplify to? | Ka = ((H+)^2)/(HA) |
| Define ionisation of water | Kw = (H+)x(OH-) = 1x10^(-14) |
| How can you work out concentration of Hydrogen ions in a strong base? | H+ = kw/(OH-) |
| Define a buffer solution | a mixture that minimises changes to pH on addition of acid or base |
| How does a buffer work? | On addition of acid, the conc of H+ is increased and equlibrium shifts to left. On addition of base the conc of OH- ions increase and these react with H+ ions to form water and equilibrium shifts to right |
| What is a buffer solution a mixture of? | Excess acid and a base or a salt |
| how can you calculate conc of H+ of a buffer solution? | H+= Ka x (HA)/(A-) |
| What substances act as the buffer in the blood? | Carbonic acid and hydrogencarbonate |
| Define equivalence point | the point of titration at which the volume of one solution has reacted exactly with the volume of the second solution. |
| Define End point | The point in a titration at which there are equal concentrations of the weak acid and conjugate base form of the indicator |
| How do you choose a suitable indicator? | pH value of the end point should be as close as possible to the titration's equivalence point |
| How do you calculate standard enthalpy change of neutralisation? | (mc/\T)/number of moles |
| Define standard enthalpy change of neutralisation | the energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of water under standard conditions |
| Define lattice enthalpy | The energy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions |
| Define Hess' Law | If a reaction can take place by more than one route then the total energy change is the same for each route (provided initial and final conditions are the same) |
| Define the standard enthalpy change of formation | The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions |
| Define enthalpy change of atomisation | The enthalpy change that accompanies the formation of one mole of gaseous atoms forms from the element in its standard state |
| why is enthalpy change of atomisation always positive? | endothermic as bonds have to be broken eg/ metallic or covalent |
| Define first ionisation energy | the amount of energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions |
| Why is first ionisation energy endothermic? | The electron being lost has to overcome the force of attraction from the nucleus |
| Define second ionisation energy | the enthalpy change that accompanies the removal of one electron from each atom in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions |
| Define first electron affinity | the enthalpy change that accompanies the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions |
| Why is first electron affinity exothermic? | The electron is attracted to the nucleus |
| Define second electron affinity | the enthalpy change that accompanies the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions |
| Why is second electron affinity endothermic | the electron is repelled by the 1 - ion and this force has to be overcome |
| What goes on the lowest level in a born haber cycle? | the ionic solid |
| How do you calculate missing values from born haber cycles? | Sum of all other enthalpy changes = enthalpy change of formation |
| Define enthalpy change of solution | the enthalpy change that occurs when one mole of an ionic compound breaks down completely in water under standard conditions |
| Define enthalpy change of hydration | the enthalpy change that occurs when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions |
| How do you calculate missing values from a Born-haber cycle containing enthalpy changes of solution and hydration? | Enthalpy changes of hydration = lattice enthalpy + enthalpy change of solution |
| How does ionic radius affect lattice enthalpy | As ionic radius increases the attraction between ions increase and lattice enthalpy becomes more exothermic (smaller ions can pack closer together) |
| how does ionic charge affect lattice enthalpy? | The larger the ionic charge the greater the attraction between ions and the more negative the lattice enthalpy |
| how does ionic size affect hydration enthalpy? | The smaller the ions the more negative the hydration enthalpy as small ions exert more attraction on water molecules |
| How does ionic charge affect hydration enthalpies? | As ionic charge increases hydration enthalpies become more negative as the ions are more attracted to water molecules |
| Define entropy | the quantitative measure of the degree of disorder in a system |
| In which reactions does entropy increase? | When there are more molecules of gas on the RHS and when a solid lattice dissolves |
| How do you calculate entropy change? | sum of entropy of products minus sum of entropy of reactants |
| define standard entropy change of reaction | the entropy change that accompanies a reaction in the molar quantities expressed in a chemical reaction under standard conditions, all reactants and products being in their standard states |
| define free energy change | the balance between enthalpy, entropy and temperature |
| What is the equation relating free energy, entropy and enthalpy? | /\G = /\H-T/\s |
| For a reaction to be feasible /\G must be... | negative |
| How do endothermic reactions take place? | /\s must be positive and T/\S>/\H |
| Define oxidation | Loss of electrons |
| Define reduction | Gain in electrons |
| What is the function of the wire in a half cell | Completes the circuit - allows electrons to be transferred between electrodes |
| What is the purpose of the salt bridge in a half cell? | Allows ions to transfer between solutions and for the circuit to be completed |
| Which metal is used as the electrode in the standard hydrogen half cell? | platinum |
| define standard electrode potential | The e.m.f. of a half cell compared with a standard hydrogen half cell measured under standard conditions |
| How do you calculate cell potential? | Most positive - most negative |
| If a reaction appears to be feasible why may it not take place in practice? | Activation energy may be too high or conditions may not be standard |
| In which direction does the more negative half equation act? | to the left |
| How are batteries recharged? | Half reactions take place in reverse |
| How do fuel cells differ from batteries? | Fuel cells rely on an external supply of fuel but do not have to be recharged |
| What is the half equation for the reaction at the negative electrode in a fuel cell? | H2+2OH-=2e-+2H20 |
| What is the half equation for the reaction in a fuel cell at the positive electrode? | 0.502+H20+2e-=2OH- |
| What is the overall reaction in a fuel cell? | H2+0.502 = H20 |
| What are advantages of fuel cell vehicles? | Less pollution and less carbon dioxide, greater efficiency |
| how can hydrogen be stored? | Absorbed within some solid materials, adsorbed onto surface of a solid material or stored as a liquid under pressure |
| what are some limitations of hydrogen fuel cells? | Large scale storage and transportation leads to a large energy usage, current adsorbers and absorbers have a limited lifetime, fuel cells require toxic chemicals in production |
| How can hydrogen be manufactured? | hydrolysis of water or reacting methane with steam |
| define transition element | A d block element which forms an ion with an incomplete d subshell |
| How do the electron configurations of copper and chromium differ? | Only one electron in 4s orbital |
| What makes transition elements good catalysts? | Variable oxidation states and provide a surface for the reaction to take place |
| What is the catalyst used in the haber process? | Iron |
| What is the catalyst used in the contact process? | vanadium oxide |
| What is the catalyst used in hydrogenation of alkenes | Nickel |
| What colour is copper hydroxide? | Blue |
| what colour is cobalt hydroxide? | blue |
| what colour is Fe(OH)2? | Green precipitate |
| What colour is Fe(OH)3? | Brick red |
| Define complex ion | a transition metal bonded to one or more ligands by coordinate bonds |
| Define a ligand | a molecule or ion that can donate a pair of electrons with the transition metal to form a coordinate bond |
| What is coordination number | the total number of coordinate bonds formed between a central metal ion and its ligands |
| What is the shape of a complex ion with coordination number of six? | Octahedral, bond angle 90 |
| Describe the position of the ligands in cis [Co(NH3)4Cl2]+ | the two chloride ligands are next to each other...one above the cobalt ion and one in the top right corner |
| What is a bidentate ligand? | A ligand that can donate two pairs of electrons to the central metal ion to form two dative bonds |
| name a hexadentate ion and some uses for it | EDTA, used to decrease concentrations of metal ions into solutions.. used in detergents, food and medical applications |
| define optical isomers | Non superimposable mirror images which can rotate plan polarised light in opposite directions |
| Define ligand substitution | a reaction in which one ligand in a complex ion is replaced by another ligand |
| What would be the colour change if [Cu(H2O)6]2+ was reacted with excess ammonia and give the formula of the product formed | Pale blue to blue precipitate to darker blue solution... [Cu(H2O)2(NH3)4]2+ |
| What is the colour change in the reaction of [Cu(H2O)6]2+ + HCl (excess) | Blue to yellow |
| What is the colour change when [Co(H2O)6]2+ is reacted with excess chloride ions? | Pink to blue |
| Why can carbon monoxide reduce oxygen transport around the body? | It can bind more strongly to haemoglobin in a irreversible reaction preventing oxygen from binding to the ion |
| In stability constants do you include the water? | No! |
| define the stability constant | the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone ligand substitution |
| What does a large Kstab value represent? | Equilibrium lies to the right...the product complex ion is more stable |
| what is the overall equation for the reaction of MnO4- with Fe2+? | MnO4- + 8H+ +5Fe2+ > Mn2++5Fe3++4H2O |
| What is the colour change in a titration involving manganese ions? | purple to colourless |
| What does a redox titration involve? | transfer of electrons from one species to another |
| What is the equation for the reaction between iodine and thiosulfate ions? | 2S2O3 2- +I2 > 2I- + S4O6 2- |
| Describe how you would carry out a titration to calculate percentage of copper in a compound | Mix the copper ions with iodine, then titrate against sodium thiosulfate until the light brown colour becomes straw coloured, then add iodine and carry on titrating until there is a colour change from blue-black to colourless. |
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