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161 Cards in this Set
- Front
- Back
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What is reaction rate? |
Change in concentration of reactants/products with unit time |
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How do we find reaction rate at a particular instant? |
Draw a tangent and calculate gradient of graph where y-axis is concentration and x-axis is time |
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What are the units of reaction time? |
moldm^-3s^-1 |
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What does a rate expression tell us? |
How certain species affect the rate of reaction. |
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Activation energy |
Minimum energy required to break bonds so that a reaction can occur |
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catalyst |
changes the rate of reaction by providing an alternative pathway to lower the activation energy without being chemically altered itself. |
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What is the 1st order of reaction and what does it mean? |
Species in rate expression is raised to the power of one. If the concentration of this species doubles so will the rate of reaction |
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What does the graph look like for a 1st order reaction? |
Directly proportional linear line through the origin |
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How do you say?: rate = [A]^1[B]^2 |
1st order reaction with respect to A 2nd order reaction with respect to B Overall, it is a 3rd order reaction |
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What does a graph for a zero order reaction look like? |
completely horizontal - any change in the species has no affect on the rate of reaction |
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what do square brackets represent? |
Concentration |
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What is the only way of finding out the order of reactions? |
Experiment: Keeping all but one reagent species the same at a constant temperature and measuring the effect on rate this has. |
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What is the rate determining step? |
The slowest stage in a reaction The overall rate of a multi-step process is governed by the slowest step |
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What is the rate constant? |
k |
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What is the only factor that affects the rate constant? |
Temperature |
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What kind of order of reaction can be left out of the rate equation? |
Zero order - since anything raised to the power of 0 is 1. |
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How can we find the initial rate of reaction and why would we? |
Draw tangent and calculate gradient when time = 0. Initial rate of reaction is the steepest. |
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How do we know whether a reactant is involved in the rate determining step? |
Species is present in the rate equation |
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What does the order of a reaction tell us in terms of the rate determining step? |
The number of molecules involved of that reagent in the rate determining step |
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What order is a reaction if it is straight on rate/(conc^2) graph? |
2nd order |
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Why may catalysts appear in the rate equation but NEVER appear in the stochiometric equation? |
The catalyst affects the rate of reaction but is chemically unchanged |
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Why does a catalyst speed up the rate of a reaction? |
Provides an alternative pathway, lowering the activation energy meaning that a higher proportion of particles have the required energy to collide more often and thus successfully react. |
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What is a heterogeneous catalyst? |
Catalyst is in a different phase to the reactants |
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Why do we use a rate constant? |
Allows us to get rid of the "proportional to" sign and use an equals sign instead |
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How do we work out the overall rate of reaction? |
Add up the orders of reaction |
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What are the units of the rate constant? |
Varies depending on the order of reactions for the species involved |
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What is dynamic equilibrium? |
Forward and backward reaction in a reversible reaction are at the same rate but there is always continuous movement. |
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What is Kc? |
equilibrium constants of products/ equilibrium constants of reactants
(EQUILIBRIUM CONSTANT) |
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The bigger the equilibrium constant... |
The further over to the right the position of equilibrium (products favoured over reactants) |
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What is Kc?: aA + bB --> cC + dD |
[C]^c + [D]^d / [A]^a + [B]^b |
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What are the units of Kc? |
Varies depending on the orders of species |
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What don't you take into account when calculating Kc? |
Solids |
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Why is Kc constant and what is the only factor that changes it? |
Kc is a mere ratio of products and reactants in a reaction at equilibrium. Temperature |
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What type of reaction does raising temperature favour? |
Endothermic |
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Why doesn't a catalyst affect Kc? |
Catalyst affects the rate of both the forward and backward reaction equally, the position of equilibrium is not affected and so the ratio Kc will not change |
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How does increasing temperature affect Kc of an exothermic reaction? |
Decreases Kc |
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How does increasing temperature affect Kc of an endothermic reaction? |
Increases Kc |
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What is an acid? |
Substance that donates protons (H ions) |
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What is a base? |
Substance that accepts a proton |
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What is the name of the acid and base reacting in pairs? |
Conjugate base/acid |
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State the two equations showing how water ionises by itself |
H20 --> H+ + OH- H20 + H20 --> H30+ + OH- |
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What is Kw and what is its value? |
Ionic product of water 1x10^-6 |
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What is pH? |
-log[H+(aq)] |
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Does a smaller or larger concentration of H+ ions lead to a smaller pH? |
Larger |
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What difference in H+ ion concentration does a difference of 1 in the pH mean? |
Tenfold |
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Is the ionisation of water exothermic or endothermic and why? |
Endothermic Energy is required to break the bonds so that it can dissociate |
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How does the value of Kw change when you increase temperature? |
Increases Position of equilibrium of ionisation/dissociation of water is shifted over to the right because it is endothermic, producing more products |
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At higher temperatures does the pH of water get higher or lower? Why isn't it actually acidic/alkaline? |
Lower Equal concentration of H+ ions and OH- ions so the water is still neutral |
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Equation for Kw |
[H+][OH-] = 1X10^-14 |
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Equation for working out [H+] in a buffer solution |
Ka x [acid]/[salt] |
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How do you work out pH for a weak acid? |
[H+] = (sq root){Ka x [HA]} pH = -log[H+] |
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How do you work out the pH for a strong acid? |
[HA] = [H+] pH = log[H+] |
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How do you work out Ka for a weak acid? |
= [H+]^2/[HA] |
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How do you work out the pH of a strong base? |
[H+] = Kw/[OH-] pH = -log[H+] |
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When doing calculations involving dilutions what changes and what doesn't? |
n=constant c=changes v=changes to total volume |
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Monoprotic acid |
Donates one proton per mole of acid |
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Diprotic acid |
Donates two protons per mole of acid |
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Amphoteric |
Substance that act as either an acid or a base |
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Strong acid |
Fully dissociates in solution |
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Weak acid |
Partially dissociates in solution |
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What does a large pKa signify? |
Weak acid |
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What side does the position of equilibrium lie for strong/weak acids? |
Strong acid = right, forward reaction is favoured Weak acid = left, backward reaction is favoured |
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What are the units for Kw? |
mol^2dm^-6 |
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How do we identify an acid in a reaction? |
Donates a proton, becoming negative |
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How do we identify the base in a reaction? |
Accepts a proton, becoming positive |
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What is dissociation? |
Breaking of covalent bonds |
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Equivalence point |
When a solution becomes neutralised |
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End point |
When the indicator changes colour |
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Describe rules of pH curves |
Starts at pH of acid, not at 0 Buffering zone present in weak acid-strong base Vertical line indicates equivalence point (this isn't present on weak acid-weak base curve) Finishes at pH of base |
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Why can't we do a titration using a weak acid-weak base? |
No definite end point - no vertical section on pH curve |
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Indicator |
pH sensitive compound (weak acid) that can exist in two different colours |
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Working range |
range of pH that an indicator can change colour in |
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Half equivalence |
Half of acid is neutralised and formed a salt [HA]=[A-] Ka = [H+] pKa = pH |
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When do you use phenolpthalein/ methyl orange? |
Phenolpthalein = strong base methyl orange = weak base (but not with weak acid) |
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Buffer solution |
Solution which prevents the change of pH upon additions of small volumes of acid/alkali |
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How many decimal points are used for pH? |
2 |
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Acidic buffer solution |
ethanoic acid and sodium ethanoate (weak acid and salt of that acid) |
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Basic buffer solution |
ammonia and ammonium chloride |
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Stereoisomerism |
Same structural formula but different arrangement of atoms in space |
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What colour is phenolpthalein in alkaline conditions? |
Red |
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What colour is phenolpthalein in acidic conditions? |
Colourless |
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What colour is methyl orange in acidic conditions? |
Red |
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What colour is methyl orange in alkaline conditions? |
Yellow |
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Name the two types of stereoisomerism |
E-Z Optical |
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What causes E-Z stereoisomerism? |
Unable to rotate around a double bond Z = same E = opposite |
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What causes optical isomerism? |
Four different substituents attached to one carbon atom resulting in a pair of non-superimposible enantiomers They rotate polarised light in opposite directions |
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Enantiomers |
Pair of chiral isomers |
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Chiral |
Optical isomers |
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How do we measure optical rotation? |
Polarimeter |
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What is + / - mean for optical isomers? |
+ = isomer rotates polarised light in a clockwise direction - = isomer rotates polarised light in an anticlockwise direction |
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Racemic mixture/racemate |
contains equal quantities of each enantiomer of an optically active compound |
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What type of reaction/mechanism is required for the synthesis of racemates? |
Nucleophilic addition across C=O of planar compound (where attack from either side is equally likely) using hydrogen cyanide |
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Why aren't racemates optically active? |
Optical activity of each enantiomer cancel each other out |
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What are the solutions and problems of using a racemic mixture as a drug? |
One isomer may be ineffective/dangerous: Seperate the two isomers to produce a pure form but this is difficult and expensive Sell the useless isomer form but this is wasteful |
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What is the chiral centre? |
Central carbon which is attached to four different substituents |
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What is the product called formed by nucleophilic addition of HCN? |
Hydroxynitrile |
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Why are the boiling points of carbonyl compounds higher than in alkanes? |
Dipole-dipole intermolecular forces in C=O carbonyl group whereas electronegativity of C-H in alkanes are too similar so only weaker Van der Waal forces present |
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Why are the boiling points of carbonyl compounds weaker than in alcohols? |
Alcohols contain stronger hydrogen bonds than the permanent dipole-dipole intermolecular force |
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Are carbonyls soluble or insoluble? |
Soluble Hydrogen bonds form with electronegative O atom in carbonyl group |
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What is formed when a nitrile is hydrolysed? |
Carboxylic acid is formed |
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What is the reaction called which introduces a CH3CO group? |
Acylation |
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Give two advantages of using acid anhydrides rather than acyl chlorides |
Cheaper Less corrosive (HCl not produced) |
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What conditions are required for nucleophilic addition of carbonyl compounds using HCN? |
Reflux in alkaline conditions |
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What is Tollens' reagent? |
Ammoniacal silver nitrate |
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Why won't you ever carry out an experiment with CN-? |
Toxic |
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Why is nucleophilic addition of CN- on aldehydes/ketones useful for organic synthesis? |
Increases carbon chain length |
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How and what are aldehydes oxidised to? |
Carboxylic acid acidified potassium dichromate - changes from orange to green
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Is it oxidation or reduction when aldehydes become carboxylic acids? |
Oxidation |
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Why can't ketones be easily oxidised? |
Requires a C-C bond to break |
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What two tests can be used to distinguish aldehydes from ketones? |
1. Fehling's: Copper oxide is reduced to red copper precipitate as aldehyde is oxidised to a carboxylic acid 2. Tollens': Silver is reduced to form a shiny mirror precipitate as aldehyde is oxidised to a carboxylic acid
Ketones give no reaction to both tests |
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What reducing agent is used for aldehydes and ketones? |
Sodium tetrahydridoborate (III) NaBH4 |
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What is the nucleophile in reduction reactions of aldehyde/ketone? |
Hydride (H-) |
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What conditions are required for the reduction of aldehyde/ketone? |
Aqueous solution of NaBH4 NaBH4 provides hydride nucleophile Water provides proton |
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What is an aldehyde reduced to form? |
Primary alcohol |
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What is a ketone reduced to form? |
Secondary alcohol |
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Are carboxylic acids soluble in water? |
Yes - hydrogen bonds can form at C=O bond |
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What are carboxylic acids isomeric with? |
Esters |
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Why are carboxylic acids acidic? |
Contains hydrogen atom in functional group which it can donate. |
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How can carboxylic acids be distinguished from any other functional group? |
React with sodium cabronate to release CO2. |
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How do the boiling points of carboxylic acids change as they increase in size? |
Also increase due to the increasing size of Van der Waal intermolecular forces |
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What is formed when a carboxylic acid reacts with an alkali ? |
Water and an ionic salt |
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Conditions required for esterification |
Alcohol and carboxylic acid in presence of strong acidic catalyst (sulfuric acid) Produces ester and water This is a reversible reaction which produces a mixture of products and reactants |
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What is formed when a carboxylic acid loses a proton? |
Carboxylate ion is produced which is stable due to the delocalisation of the negative charge over the whole group |
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Conditions required for hydrolysis of ester |
ester and water in presence of strong acidic catalyst (sulfuric acid) to produce a carboxylic acid and alcohol. Reversible reaction producing an equilibrium mixture OR ester and aqueous NaOH to produce salt and alcohol |
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What is the formula of glycerol? |
1,2,3-triol |
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How do you name esters? |
Alkyl group that replaced the hydrogen from when it was a carboxylic acid goes first Parent acid dictates the -oate end |
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What is formed when a carboxylic acid reacts with sodium hydrogencarbonate? |
Salt and water and carbon dioxide |
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How can you convert a carboxylate salt into a fatty acid? |
Add HCl |
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What is glycerol used for? |
Food colourings Prevent ointments drying out Plasticise materials |
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Describe saponification |
Alkaline hydrolysis of triglycerides to produce sodium salts (soap) Ester is boiled in sodium hydroxide to produce glycerol and sodium salt |
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State reaction for producing biodiesel |
Triester and methanol react to produce a methylester and glycerol |
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What type of reactions take place for acylation to occur? |
Addition-elimination |
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What is produced when acyl group reacts with ammonia? |
Amide |
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What is produced when an acyl group reacts with a primary amine? |
N-substituted amide |
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What is produced when an acyl group reacts with an alcohol? |
Ester |
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What is produced when an acyl group reacts with water? |
Carboxylic acid |
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What makes acid chloride a good acylating agent? |
Chlorine atom is very electronegative and so withdraws electrons from carbonyl carbon making the carbon more positive and thus open for attack. |
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State reactivity of nucleophiles in addition-elimination reactions |
Ammonia - produce amide Amine - produce N-sub-amide Alcohol - produce ester Water - produce carboxylic acid |
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What do acid anhydrides produce in acylation reaction which differs from acyl chlorides? |
Acid anhydrides produce carboxylic acids Acyl chlorides produce HCl |
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Nucleophile |
Electron pair donor |
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Describe the structure of benzene |
Planar regular hexagon of carbon atoms, each of which is bonded to a single hydrogen atom |
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Explain the aromatic stability of benzene |
Electrons are delocalised in a ring where they are spread over more than two atoms forming a pi-bond of high electron density. |
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Problems with Kekule's model of benzene |
He thought that there would be three double carbon bonds but if there were it should readily undergo electrophilic addition Hydrogenation should be thrice of cyclohexane's but it is less, proving that it is more stable X-ray crystallography showed that the structure of benzene to have bonds of all equal length. Kekule's model would have been assymetrical. |
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Conditions required for nitration of arene |
Concentrated nitric acid and concentrated sulfuric acid produces electrophile (NO2+) |
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How can we tell that an arene is being combusted? |
Smokey flame due to high carbon:hydrogen ratio |
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What is the electrophile for nitration reactions? |
Nitronium ion NO2+ |
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State equations for formation of electrophile for nitration of arene |
HNO3 + H2SO4 -->HSO4- + H2NO3+ H2NO3+ --> NO2+ + H2O |
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What is the catalyst for Friedel-Crafts acylation reactions |
Aluminium chloride AlCl4- |
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State equation of catalyst formation for Friedel-Crafts reaction |
AlCl3 + RCOCl --> RCO+ + AlCl4- |
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What is the formula and when is the acylium ion involved? |
RCO+ used in Friedel-Craft reaction for formation of electrophile aluminium chloride AlCl4 |
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Conditions for Friedel-Crafts acylation |
Acyl chloride and anhydrous aluminum chloride catalyst Electrophile = acylium RCO+ |
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What are quaternary ammoniu salts used for? |
Fabric softener |
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How many hydrogens are attached to the nitrogen atom on a primary amine? |
3 |
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How many hydrogens are attached to the nitrogen atom on a secondary amine? |
2 |
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State three ways of preparing amines |
1. Successive nucleophilic substitution using excess ammonia on haloalkanes 2.Reducing nitriles using a nickel catalyst 3.Making phenylamine |
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Do amines have a higher or lower boiling point and why? |
Lower Nitrogen is less electronegative than oxygen and so the hydrogen bonds intermolecular forces are weaker and thus require less energy in order to be overcome |
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Are amines soluble in water? What is the exception? |
Yes, hydrogen bonds can form Phenylamine isn't due to the benzene ring |
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What is formed when an amine reacts with an acid |
Ionic salt Amine acts as a base |
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How can we regenerate the amine from its ionic salt |
use a strong base like sodium hydroxide |
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Explain base strengths of amines |
Alkyl group's inductive effect feeds electrons towards the nitrogen atom making its lone pair more exposed for attaching onto a H+ ion Secondary alkylamine is a stronger base than a primary alkylamine Arylamines are the weakest bases because the aryl group's inductive effect feeds away from the nitrogen atom. |
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What is the downside of amine preparation via nucleophilic substitution and how can this be overcome? |
Sucessive and so a mixture of different amines are produced However, these can be seperated via fractional distillation |
