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Chemistry Year 12 > module 3.2 > Flashcards

module 3.2 Flashcards

1
Q

what is activation energy

A

the minimum emery particles need for collisions to be successful and result in reaction

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2
Q

what are standard conditions

A

298K and 1atm

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3
Q

what is the enthalpy change of reaction

A

the enthalpy change for a given reaction

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4
Q

what is the enthalpy change of formation

A

the enthalpy change when forming 1 mol of a compound from its elements

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5
Q

what is the enthalpy change of combustion

A

enthalpy change for the complete combustion of 1 mol of a substance

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6
Q

what is the enthalpy change of neutralisation

A

the enthalpy change for the formation of 1 mol of water from a neutralisation reaction

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7
Q

what is the average bond enthalpy

A

the enthalpy change for breaking 1 mol of bonds in gaseous molecules

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8
Q

what is hess’ law

A

the enthalpy change of a reaction is independent of the route taken

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9
Q

what do the arrows in hess cycles mean

A

up is making bonds down is breaking bonds (goes towards it if it’s being made or away if it’s breaking up)

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10
Q

what is chemical energy

A

the potential energy stored in bonds

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11
Q

what is enthalpy

A

chemical energy

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12
Q

what concentration should every solution be in enthalpy calculations

A

1mol dm^-3

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13
Q

values of enthalpy change of formation

A

usually but not exclusively exothermic

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14
Q

values of enthalpy change of combustion

A

always exothermic

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15
Q

values of enthalpy of neutralisation

A

always exothermic

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16
Q

what is the enthalpy change of neutralisation strong acids and strong alkalais

A

-57 kJ mol^-1

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17
Q

what’s enthalpy change unit

A

kJ mol^-1

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18
Q

what’s the calorimetery equation and what does each letter stand for with units

A

q=mc@T
q= heat energy J
m= mass g
c= specific heat capacity J g^-1 K^-1
@T= temperature change K (but change in °C is the same)

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19
Q

what is specific heat capacity

A

the energy required to raise the temperature of 1g of a substance by 1K

20
Q

how do you determine enthalpy change from calorimetry equation

A

work out q, then divide by the moles (because enthalpy change is the energy needed for one mole)

21
Q

what’s the enthalpy of formation for elements in their standard state

A

0

22
Q

where will the enthalpy change of neutralisation arrow point

A

towards the water

23
Q

how do you deal with O2 and CO2 in enthalpy cajnge of combustion

A

ignore it because they’re products and would cancel out

24
Q

what is collision theory

A

for a reaction to happen particles must collide with enough energy (activation energy) for the collisions to be successful

25
Q

what are the five factors that affect rate of reaction

A

temperature pressure catalyst concentration surface area

26
Q

why do catalysts increase rate of
reaction

A

they lower activation energy by providing an alternate pathway so a greater proportion of particle collisions that have the activation energy so more frequent successful collisions

27
Q

what is a heterogeneous catalyst

A

catalyst is in a different phase (state) to the reactants

28
Q

what is a homogeneous catalyst

A

catalyst is in the same phase (state) as the reactants

29
Q

how does a heterogeneous catalyst work

A

reactants ADSORPED to the active site on the surface of the catalyst, they form weak bonds with metal atoms whcih uses some bonding electrons thus weakening the bonds. REACTION takes place which requires less energy. DESORPTION is the last step when the products are released

30
Q

what is catalyst poisoning

A

when the surface of a catalyst is coated in a substance that cant desorb thus removing potential active sites and decreasing efficiency

31
Q

what is dynamic equilibrium in a closed system

A

when the rate of reaction is the same in both directions of a reversible reaction, meaning the concentrations of the reactants and products don’t change

32
Q

what is le chateliers principle

A

if equilibrium is disturbed by changing the conditions the position of equilibrium shifts to counteract the change to re-establish an equilibrium

33
Q

what condition permanently affects equilibrium constants and why

A

temperature change because it affects the energy in the reaction rather than the chemicals (which can be rectified)

34
Q

how would:
aA + bB <=> cC + dD
be put in an equation to work out Kc

A

[C]^c [D]^d
—————- = Kc (constant)
[A]^a [B]^b

35
Q

what are the rules when constructing an equilibrium constant equation

A

square brackets around the equilibrium concentration in mol dm^-3 raised to the power of the stoichiometry number with reactants over products

36
Q

how do you work out the units of equilibrium constants

A

use the powers from the stoichiometry numbers and use indice laws from the base mol dm^-3

37
Q

where is equilibrium if Kc= 1

A

halfway between the reactants and products

38
Q

what happens to equilibrium if K<1 (smaller than 1)

A

the reactants are being favoured so equilibrium shifts left to use up more reactant

39
Q

what happens if K>1 (bigger than 1)

A

the reaction is product favoured so equilibrium shifts right to use up more products

40
Q

what word should you use when discussing changing concentration on Kc values

A

restores Kc to x

41
Q

how do you set up calculations for Kc

A

create balanced equation with state symbols
Initial Change Equilibrium (in mol)
use c=n/V (remember mol dm^-3) if no volume stated use V it should cancel out later
sub into usual equation

42
Q

what is X in [X] in Kc calculations

A

the equilibrium concentration

43
Q

what are the axis on a boltzmann distribution

A

x = energy
y = number of molecules with a given energy

44
Q

what does the area under a boltzmann curve represent

A

total number of molecules in the sample

45
Q

what must you rememebr when drawing a boltzmann

A

must begin at the origin
once it starts coming down it never goes up again
never touches the x axis after the origin

46
Q

how does a boltzmann curve change with increased temperature

A

flattens and broadens

47
Q

how does a catalyst affect a boltzmann graph

A

curve stays the same, the activation energy just shifts left

Chemistry Year 12 (7 decks)

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