Chem 4

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Define the rate of a reaction
increase in concentration of products per unit time
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What happens to Kc when temperature decreases in an endothermic reaction
decreases
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What happens to Kc when temperature increases in an endothermic reaction
Increases
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What happens to Kc when temperature decreases in an exothermic reaction
increases
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What happens to Kc when temperature increases in an exothermic reaction
decreases
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What happens to Kc when pressure increases
no effect
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What happens when Kc is greater than 1
It means equilibrium is over to the right as the products predominate the reactants
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What happens when Kc is less than 1
It means that equilibrium is over to the left as the reactants predominate the products
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Define an acid
A proton donor
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Define a base
A proton acceptor
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What is pH
-log10[H+]
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In a titration, what is the equivalence point?`
The point at which sufficient base has been added to neutralise the acid (or vice versa)
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What is a buffer
A solution that resists change in pH
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What happens when you add an alkali to an acidic buffer (made of a weak acid and its soluble salt)
Weak acids (HA) dissociate to form H+ and A-. The concentrations of the H+ and A- are very small as the HA does not fully dissociate. If you add OH- ions, they react with the HA to form H2O thus removing the OH- and so pH remains almost the same
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What happens when you add an acid to an acidic buffer (made of a weak acid and its soluble salt)
Equilibrium shifts to the left as the H+ reacts with the A_ to form HA. As the soluble acid salt fully dissociates to form A-, this increases the supply of A- ions meaning the added H+ ions can be mopped up so pH remains almost constant
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Define stereoisomerism
Same molecular formula but different arrangement of the atoms in space
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What are opticat isomers and how do they occur
They are two isomers that are mirror images of each other. They occur when a carbon (the chiral centre) has for different constituents bonded to it
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How can you distinguish between two optical isomers
Plane plarised light is passed through two different solutions of the isomers at the same concentration. The positive isomer rotates the light clockwise and the negative isomer rotates it anti clockwise
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What is a racemic mixture
A mixture of two equal enantiomers. racemic mixtures are not optically active because the effects of the two isomers cancel each other out
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What types of reactions do aldehydes and ketones undergo
redox reactions and nucleophillic addition reactions
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Name the reagent used to turn an aldehyde or ketone into a hydroxynitrile
HCN
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Name the reagents and conditions used to oxidise aldehydes
Potassium dichromate acidified with H2SO4. Under reflux
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What happens to Kc when temperature decreases in an endothermic reaction

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decreases

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What happens to Kc when temperature increases in an endothermic reaction

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Card 4

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What happens to Kc when temperature decreases in an exothermic reaction

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What happens to Kc when temperature increases in an exothermic reaction

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