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Chemistry A level > chap 6- chemical industry > Flashcards

chap 6- chemical industry Flashcards

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1
Q

define reaction rate

A

the change in amount of reactants or products per unit time

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2
Q

how can you measure rate of reaction using pH measurement

A

monitor pH of reaction mixture using pH meter or probe connected to a data logger. this can be converted into units of concentration because H+ = 10^ -pH

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3
Q

how can you measure rate of reaction using gas volume

A

collect it in a gas syringe and record how much you’ve got at regular intervals

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4
Q

how can you work out rate of reaction using mass change

A

if a gas is given off the system will lose mass. this can be measured at regular intervals using a balance

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5
Q

how can you follow rate of reaction using colour change

A

if one of the reactants or products is coloured you can use a calorimeter that measures the absorbable of the solution and the more concentrated the colour, the higher the absorbance which can be used to calculate the concentration using a calibration curve

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6
Q

how can you work out rate of reaction using titrations

A

take small samples of the reaction mixture at regular intervals and titrate them to calculate concentration

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7
Q

equation for calculating the initial rate

A

amount of reactant used or product formed / time

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8
Q

outline the initial rates method

A

time how long it takes for a set amount of product to form at the beginning of the reaction. repeat several times and change the conc of one reactant each time

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9
Q

what 3 assumptions do you make when doing an initial rates reaction

A
  1. the concentration of the other reactants isn’t changing significantly
  2. temperature stays constant
  3. reaction has not proceeded too far when you take measurement
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10
Q

what is a clock reaction

A

(type of initial rates reaction) where you measure how the time taken for a set amount of product to form changes as you vary the conc of one reactant

has an easily observable end point (colour change)

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11
Q

outline the iodine clock reaction

A

small amount of sodium thiosulfate and starch (indicator) added to excess hydrogen peroxide and iodide ions in acid solution
sodium thiosulfate reacts with any iodine that forms but once all sodium thiosulfate is used up and more iodine formed will stay in solution so starch indicator turns solution blue/black

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12
Q

how to write a rate equation

A

for a reaction such as A + B = C + D
the rate equation would be:
rate = k (A)^m x (B)^n
where m and n are the respective orders

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13
Q

what is k in a rate equation

A

the rate constant- the bigger it is the faster the reaction

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14
Q

what does 0 order mean

A

if the conc of the reactant changes and the rate stays the same

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15
Q

what does 1st order mean

A

if the conc of the reactant and the rate of reaction are proportional

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16
Q

what does 2nd order mean

A

if the rate of reaction is proportional to the conc of reactant squared

17
Q

what is the overall order of a reaction

A

the sum of the orders of the different reactants

18
Q

how does half life vary with order of a reaction

A

0 order: rate doesn’t change as conc falls. half life decreases as reaction goes on
1st order: half life is constant but rate decreases with conc
2nd order: half life increases as reaction goes on

19
Q

how can you work out the rate constant using the half life

A

k = ln2/ half life

20
Q

what 3 things do particles need in order for a reaction to happen

A
  1. collide with each other
  2. have enough energy to react (activation enthalpy)
  3. have the right orientation
21
Q

what is the arrhenius equation in logarithmic form

A

ln k = - Ea/ RT + lnA

22
Q

what is the rate determining step in a reaction

A

the slowest step and therefore determines the overall rate

23
Q

what does the reaction order tell us about the rate determining step

A

the order of a reaction with respect to a certain molecule tells us how many molecules of that reactant there are in the rate determining step

24
Q

what happens to the equilibrium if you increase the temperature

A

equilibrium shifts in endothermic direction to absorb the extra heat. Kc rises if more product is formed

25
Q

what happens to equilibrium if you increase the pressure

A

equilibrium shifts to the side with fewer gas molecules in order to reduce the pressure

26
Q

what are the ideal and actual conditions used for the haber process

A

carried out at 400c and 200 atm because high pressure favours the forward reaction but too high is expensive and can be dangerous
high temp increases reaction rate but forward reaction is exothermic so a lower temp is favourable but too low would make reaction rate too slow

27
Q

how can you use calorimetry to find the equilibrium conc

A

use calorimetry to find the absorbance of the wavelength of light absorbed by the coloured substance and then use a calibration curve to find the conc

28
Q

how can you use pH to find the equilibrium conc

A

pH probe to find the pH then do a pH calculation to find the conc

29
Q

why can you not use titrations to find the concentration at equilibrium

A

adding an acid to the equilibrium mixture in order to titrate would cause some alkali to react forming salt and water so then the conc of alkali would decrease which would shift the equilibrium

30
Q

why is N2 (nitrogen as a diatomic molecule) unreactive

A

it forms a triple bond due to sharing 3 pairs of electrons and this is hard to break

31
Q

what is a ligand

A

an ion or molecule attached to a metal atom

32
Q

how can an N atom act as a ligand

A

because it has a lone pair of electrons so it can form a dative covalent bond with transition metals forming complex ions

33
Q

what is NO

A

nitrogen monoxide/ nitric oxide/ nitrogen (ii) oxide- a colourless gas

34
Q

what is N2O

A

dinitrogen monoxide, nitrous oxide, nitrogen (i) oxide- sweet smell and colourless

35
Q

what is NO2

A

nitrogen dioxide or nitrogen (iv) oxide- brown gas, sharp odour, toxic

36
Q

how can you test for ammonium ions

A

add NaOH and gently heat. if ammonium is present they will react with hydroxide ions and ammonia gas will be evolved which is alkaline and so will turn damp red litmus paper blue

37
Q

how can you test for nitrate ions (NO3-)

A

warm the solution with NaOH and some aluminium foil, the aluminium will reduce the nitrate ions to produce ammonia gas which will turn damp red litmus paper blue

Chemistry A level (10 decks)

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