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Chemistryyy > chemsitry - energetics and electrolysis > Flashcards

chemsitry - energetics and electrolysis Flashcards

1
Q

what is the symbol for the energy change that accompanies a reaction?

A

delta(change in) H

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2
Q

in exothermic reactions:
energy is given ? or ? when products form and the ? of the surroundings gets hotter/ increases

A

out, released, temperature

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3
Q

in exothermic reactions:
energy is taken ? when products form and the ? of the surroundings gets colder/ ?

A

in, temperature, decreases

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4
Q

Why are delta H values for Exothermic reaction negative?

A

As energy is released to the surroundings, so the products have less/lower energy than the reactants

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5
Q

Why are delta H values for endothermic reactions positive?

A

As energy is taken in from the surroundings, the products have more/higher energy than the reactants

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6
Q

what is the activation energy?

A

the minimum amount of energy that must be supplied in order to break the bonds in the reactants particles to initiate the reaction

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7
Q

old bonds between atoms in reactants are ?

A

broken

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8
Q

new bonds between atoms in products are ?

A

formed/made

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9
Q

what does bond breaking require and what type of process is this?

A

energy, so it is an endothermic reaction

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10
Q

what does bond breaking release and what type of process is this?

A

energy, it’s an exothermic reaction

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11
Q

Overall whether a reaction is endothermic or ? depends on the difference of ? needed to break old ? and the ? released in forming/? new bonds

A

exothermic, energy, bonds, energy, making

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12
Q

Exothermic reactions - when more ? is released in the formation of NEW bonds than is needed to ? old bonds. so delta H values for Exothermic ? are ?

A

energy, break, reactions, negative

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13
Q

Endothermic reactions - when less ? is released in the formation of NEW bonds than is needed to ? old bonds. so delta H values for Endothermic ? are ?

A

energy, break, reactions, positive

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14
Q

Exothermic reactions - greater than equation

A

energy released when new bonds are formed > energy required when old bonds are broken

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15
Q

Endothermic reactions greater than equation

A

Energy required to break the old bonds / when old bonds are broken> energy released when new bonds are formed

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16
Q

Energy profiles : what does an exothermic profile look like?

A
  • have two axis - only y axis is labelled with energy
  • start with a horizontal line at the top with the reactants
  • draw a lower horizontal line at the bottom for the products
    then draw a looping arrow up from the reactants down to the products -the peak of the arrow to the reactants should be the activation energy
  • the distance between reactants and products is delta H
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17
Q

energy profiles - what does an endothermic one look like?

A
  • have two axis - only y axis is labelled with energy
  • start with a horizontal line at the bottom with the reactants
  • draw a higher horizontal line at the bottom for the products
    then draw a looping arrow up from the reactants up to the products -the peak of the arrow to the reactants should be the activation energy
  • the distance between reactants and products is delta H
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18
Q

equation for delta H

A

sum of bonds broken - sum of bonds formed

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19
Q

4 steps to bond energy calculations
1 - write out symbol ? using displaced formulae showing all ?
2. work out energy needed to ? bonds
3. work out energy ? when bonds are ?
4. work out energy ? - delta ? using :
either :
• energy ? to break bonds - energy released when bonds are ?
or
• ? of bonds broken - sum of bonds ?

A

equation, bonds
break
released, formed
change, H
needed/required, made
sum, made

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20
Q

what is the alternative method for bond energy calculations?

A
  1. highlight the bonds that change between the reactants and the products
  2. only calculate the energy needed to break these bonds/ the energy released when new bonds are made
  3. then use the delta H equation to work out whether the equation is exothermic or endothermic (by the negative or positive delta H)!!!
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21
Q

what is the half equation for hydroxide being oxidised

A

4(OH-) –> 2(H20) +2(02) + 4e-

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22
Q

solid ionic ? do not conduct ? as there are no free ? to flow through the structure and all the charged ? are locked into a lattice ? in the solid ; the ions are not ? to move

A

compounds, electricity, electrons, particles/ions, structure, free

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23
Q

why is the cathode negative and therefore which ions go to it (and what is formed at it)?

A

because it has an excess of electrons, the cations go to it and so the metal element is formed at the cathode

24
Q

why is the anode negative and therefore which ions go to it (and what is formed at it)?

A

because it has a lack/shortage of electrons (so is positive), the anions go to it and so the non-metal element is formed at the anode

25
Q

given that electrons are taken from the ? and given to the cathode, there is an overall flow of ? and so an electric ? is said to flow

A

anode, electrons, current

26
Q

when do ionic compounds conduct electricity and why

A

when they are dissolved in water or are in molten form as the ions are free to move

27
Q

what are molten liquids and solutions (which both conduct electricity) also known as

A

electrolytes

28
Q

how can a more reactive metal than carbon be extracted?
1. heat and ? metal to free ?
2. pass an electric ? through the molten ?
3. detail what happens at the cathode - half ?
4. detail what happens at the ?, half equation
5. give reasons for why ? is expensive

A

melt, current, metal, equation, anode, electrolysis

29
Q

in what form is aluminium found in the earth’s crust and what is this called

A

as a compound called bauxite (Al2O3)

30
Q

before electrolysis, aluminium oxide has to be melted, however due to its high ? point this can be very ? and would require lots of heat ? . because of this, a substance called ? is added which dissolves the ? oxide and decreases the ? point - making the process simpler and ?

A

melting, expensive, energy, cryolite, aluminium, melting, cheaper

31
Q

why is an electrolysis of a solution more complicated?

A

as it is dissolved in water there will be some dissociated ions of hydroxide and hydrogen

32
Q

during an electrolysis of a solution what is usually made at the cathode plus half equation and what is the exception

A

hydrogen is usually made ( 2H+ + 2e- –> H2), unless an ion of a more unreactive metal than hydrogen eg copper is present, in which case we make the metal!! x

33
Q

during an electrolysis of a solution what is usually made at the anode plus half equation and what is the exception

A

oxygen is usually made ( 4OH- –> O2 + 2H2O + 4e- ), unless an ion of a halide, eg bromide is present, in which case a halogen is made

34
Q

why is aluminium used in planes?

A

it’s strong and malleable, low density and corrosion resistant

35
Q

what are magnalium and duralumin both used for?

A

to make bikes and planes

36
Q

what is duralumin

A

an alloy of copper and aluminium

37
Q

how can solid sodium hydroxide be recovered from a solution of sodium hydroxide?

A

evaporating away the water

38
Q

test for hydrogen?

A

burns in air with a squeaky pop/ put lit splint in presence of hydrogen and it produces a squeaky pop

39
Q

test for chlorine
test for oxygen

A
  • turns damp blue litmus paper red then bleached it white
  • oxygen relights glowing splint
40
Q

why is hydrogen normally made at the cathode?

A

as it is always the ion which is lower in the reactivity series that is discharged and gains electrons - and so hydrogen is normally below most metals in the reactivity series

41
Q

if copper forms at the cathode what does it look like?

A

brown coating on the electrode

42
Q

if sodium forms at the cathode what does it look like?

A

grey coating on the electrode

43
Q

if hydrogen forms at the cathode what does it look like?

A

bubbles of gas

44
Q

if oxygen forms at the anode what does it look like?

A

bubbles of gas form that do not bleach damp blue litmus paper

45
Q

if chlorine forms at the anode what does it look like?

A

bubbles of gas that do bleach damp blue litmus paper, should also smell like swimming pool water!!!

46
Q

what happens at the cathode and the anode in the electrolysis of copper sulphate using inert (graphite) electrodes

A

at the cathode, copper is formed (reduction)
at the anode, oxygen is formed (oxidation)

47
Q

what happens in the electrolysis of copper sulphate using copper electrodes (non inert) and how is this different to other electrolysis (and what happens at the two electrodes)

A

as they are copper electrodes - the negative cathode attracts Cu2+ ions from the solution, while the positive anode replaces the Cu2+ ions - so the cathode increases in mass and then anode decreases. at the cathode, copper is made and at the anode copper ions are made - which is different as normally two different products are made

48
Q

Purification of copper using electrolysis what happens?
1. Copper in the ? anode forms copper ? which dissolve into the electrolyte (?)
2. The ? ions move to the ? copper cathode and react to form a layer of pure ?
3. Any impurities from the ? copper anode sink to the bottom of the cell forming a ?

A

impure, ions, CuSO4
copper, pure, copper
impure, sludge

49
Q

what does the anode and cathode start off as at the start of the purification of copper electrolysis and what is the electrolyte?

A

the anode is a big lump of impure copper, while the cathode is a thin piece of pure copper and the electrolyte is CuSO4 solution

50
Q

electrolysis of sulphuric acid - what is made at the electrodes and what is the ratio of these substances?

A

at cathode - hydrogen is made and at anode oxygen is made. the ratio is 2:1 of hydrogen to oxygen - for every one molecule of oxygen there are two hydrogen molecules

51
Q

what is a conductometric titration

A

a titration in which the electrical conductivity is measured as an acid is to tested against an alkali

52
Q

Is silicon dioxide an electrolyte as a liquid or as dissolved in water?

A

no as it is just a melted covalent substance, and the same in water

53
Q

what two substances are electrolysed when in liquid or aqueous form?

A

ionic substances or acids

54
Q

how would electrical conductivity change as increasing amount of sulphuric acid is added to 25cm cubed of barium hydroxide?

A

the conductivity initially falls as the number of ions decreases because of the reactions occurring - making the mixture more and more neutral. however after the perfect ratio of barium hydroxide and sulphuric acid is surpassed, the conductivity keeps increasing as increasing amounts of sulphuric acid in excess are added providing more ions for higher conductivity

55
Q

write the two ionic equations for the reaction between barium hydroxide and sulphuric acid

A

H+(aq) + OH-(aq) —> H2O(l)
Ba2+(aq) + SO4 2- (aq) —> BaSO4(s)

56
Q

conductometric titration involving sulphuric acid and barium hydroxide - what are the pHs of both solutions

A

1/0 for the acid and 13/14 for the hydroxide

57
Q

would aqueous sulphuric acid and barium hydroxide be electrolytes or not?

A

yes as they are either acids or ionic and are dissolved in water so the ions are free to move!!!

Chemistryyy (40 decks)

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