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B5 Energetics 2 Flashcards

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1
Q

Define Lattice Enthalpy

A

The enthalpy change when 1 mole of an ionic compound is formed from its ions in their gaseous state
under standard conditions

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2
Q

is lattice enthalpy exo or endo

A

exo

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3
Q

state and explain whether Nacl or Mgcl2 will have the highest melting point

A
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4
Q

what are the 2 ways of calculating lattice enthalpy

A

Experimental values - born harder cycles - using known energy changes from experiments

Theoretical changes - calucted using physics caluculations- assume ions are perfect spheres

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5
Q

Draw a Born- Harber cycle

A
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6
Q

standard enthalpy of formation

A

enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

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7
Q

standard enthalpy of atomisation

A

enthalpy change when one mole of a gaseous atoms forms from its element in its standard state under standard conditions

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8
Q

is standard enthalpy of atomisation exo or endo

A

always endothermic

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9
Q

standard enthalpy of atomisation equations

A
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10
Q

Atomisation equation for iodine

A
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11
Q

First ionisation enthalpy

A

enthalpy change when one electron is removed from each atom in one mole of gaseous atoms to form +1 ions

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12
Q

First ionisation enthalpy equation

A
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13
Q

second ionisation enthalpy

A

enthalpy change when one electron is removed from each +1 ion in one mole of gaseous +1 ions to form +2 ions

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14
Q

second ionisation enthalpy equation

A
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15
Q

first electron affinity

A

enthalpy change when one electron is added to one mole of gaseous atoms to form -1 ions

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16
Q

First electron affinity of chlorine equation

A

-ve

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17
Q

is second electron affinity exo or endo

A

endo

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18
Q

Born harber cycle of sodium chloride

A
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19
Q

write an equation for the standard enthalpy change of atomisation of bromine

A
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20
Q

What must you remember when using born harber cycle

A

state symbols

definitions

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21
Q

write the equation of the second electron affinity of oxygen - state and explain whether this will be endothermic or exothermic

A

endothermic

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22
Q

When must data be multiplied by 2 in a Born-Haber Cycle

A

When the product has a molar mass of two

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23
Q

When calculating lattice enthalpy from a Born-Haber Cycle, how should the equation be structured

A

With enthalpy of formation on the left-hand side of the equation, and the route on the right

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24
Q

Going clockwise round a Born-Haber cycle, what is the order of the processes

A

Atomisations, Ionisations, Electron Affinities, Lattice Enthalpy

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25
What must be remembered with electrons in Born-Haber Cycles
The electrons produced by ionisation energies are used in the affinities
26
what happens when we put ionic compounds into solution
ions are separated from the lattice and surrounded by water molecules
27
write an equation to show the lattice enthalpy of sodium chloride
28
the charge on water molecules are attracted to the charge on the ions, these interactions are known as
ion - dipole interactions
29
when ions are separated from the lattice and surrounded by water molecules they are considered to be
in solution (aq) and hydrated
30
Define Enthalpy Change of Solution
enthalpy change when one mole of a solute dissolves in water to give a very dilute solution - avoids ions interacting
31
Define Enthalpy Change of Hydration
enthalpy change for forming a solution of ions from 1 mol of gaseous ions Na + (g) + aq ---> Na+ (aq)
32
is enthalpy change of hydration exo or endo
exo -ve
33
Enthalphy of hydration will depend on
ionic radius charge - charge density more negative more exothermic
34
How do we calculate Enthalphy change of solution
35
Draw a solution enthalpy cycle, with general terms
36
Draw a solution enthalpy cycle, for sodium chloride
37
explain this entalphy level diagram
38
explain this entalphy level diagram
39
explain this enthalpy level diagram
40
what about non polar solvents
41
describe an experiment you could conduct to determine the enthalpy change of solution of NACl
42
factors that effect standard lattice enthalpy
charge size, ionic radius - charge density
43
factors that effect standard lattice enthalpy key words
charge ionic radius lattice entalphy attraction
44
45
46
Design an experiment to determine the enthalpy change of solution of magnesium chloride (MgCl2) - you should include appropriate measurements to use and names of all equipment used. Include details on how to make your experiment accurate and how to conduct the calculation required. (6 marks)
a) 1. measure water with named appropriate apparatus (measuring cylinder) 2. suitable volume/mass in the range 10 - 200cm3/g 3. into insulated container/polystyrene cup 4. add known mass of MgCl2(s) 5. use of 'before and after' weighing method b) 1. record initial temperature (min 2 measurements) 2. record T at regular timed intervals for 5+ mins/until trend seen 3. plot T vs time c) 1. extrapolate lines to when solid added (to find initial and final T) 2. Tfinal - Tinitial 3. Q=mc change in T 4. amount = mass/Mr 5. change Hsoln = -q/8.39x10-3
47
What is the effect on deltaT, and the enthalpy change of solution, when the volume of water in an experiment is doubled
deltaT will half, as the same amount of energy is transferred to double the volume of water. Enthalpy of solution stays the same as the ratio of energy releases: moles is the same, and so the same energy is released per mole.
48
What is the effect on deltaT, and the enthalpy change of solution, when the mass of the solid is doubled
deltaT will double as double the amount of energy is being transferred to the same volume of water. Enthalpy of solution stays the same, as the ratio of energy released: moles is the same, and so the same amount of energy is released per mole.
49
How does a greater ionic radius affect the attraction to ions
Weaker attraction to ions
50
How does a smaller ionic radius affect the attraction to ions
Stronger attraction to ions
51
How does a greater ionic charge affect the attraction to ions
Stronger attraction to ions
52
How does a smaller ionic charge affect the attraction to ions
Weaker attraction to ions
53
Explanation of comparing two lattice enthalpies with different ionic radii
Lattice enthalpy of X is more exothermic than Y. As ion X is smaller, so has a smaller ionic radius. Therefore attraction to Z- ions is stronger. So more energy is needed to break ionic bonds between ions.
54
Explanation of comparing two lattice enthalpies with different ionic charge
Lattice enthalpy of X is more exothermic than Y. As X has a 2+ charge, compared to Y which has a 1+ charge. X has a greater ionic charge. Therefore attraction is stronger to Z- ions. So more energy is needed to break ionic bonds between ions. more charge = more exothermic lattice enthalpy
55
Dissolving energetically favourable
if Ah soln is negative dissolving is energetically favourable
56
Define entropy
level of diserpsion of ennergy within and system and the level of disorder - more random/ disordered --> higher entropy
57
Describe and explain how entropy changes from (s) to (l) [or (l) to (g)]
Entropy increases as disorder increases. As liquid particles have more disorder than solid particles.
58
Describe and explain how entropy changes from (l) to (s) [or (g) to (l)]
Entropy decreases as disorder decreases. As solid particles have less disorder than liquid particles.
59
Describe and explain how entropy changes when there are more moles of gas as products
Entropy increases as disorder increases. As more gaseous molecules are produced.
60
Describe and explain what happens to entropy when there are less moles of gas in the products
Entropy decreases as disorder decreases. As less gaseous molecules are produced.
61
Equation to calculate deltaS
62
Unit for entropy
J K-1 mol -1 remember to divide by 1000
63
symbol for entropy
64
if a system changes to become more random, energy can be spread out more
65
entropy changes
66
positive entropy change
solid - gas less moles to more moles in equations
67
Units for deltaS
J K(-1) mol (-1)
68
Free energy
overall energy change in a chemical reaction * The enthalpy change (ΔH) - This is the energy transfer between the chemical system and the surroundings The entropy change at the temperature of reaction (TΔS) - This is the dispersal of energy within the system at a given temperature
69
Gibb’s Free Energy Equation
70
Gibb’s Free Energy Equation labeled
71
What is crucial to do when calculating Gibb’s Free Energy
Always divide deltaS by 1000, so that it is in kJ
72
What must be done when calculating Gibb’s free energy with the units
Divide deltaS by 1000 so it is in kJ
73
Why must deltaS be divided by 1000 when using it in Gibb’s Free Energy equation
As deltaG is in kJ, and deltaS is in J
74
Units for deltaG
kJ mol(-1)
75
When is a reaction feasible
When deltaG is equal to/below zero
76
When does the feasibility of a reaction change
When deltaG = 0 and find T
77
Describe and explain how increasing temperature affects feasibility
Feasibility increases as temperature increases. As -TdeltaS becomes more negative than deltaH, so deltaG decreases.
78
What is the gradient when Gibb’s Free Energy is graphical
- deltaS
79
Explain how Gibb’s Free Energy is related graphically
80
shown graphically
81
Draw a graph and annotate where: * Point where feasibility changes * deltaH * What the gradient represents
82
2nd electron affinity is
end0
83
AG - for it be feasible
must be -ve
84
why does a feasible reaction not get observed
kinetics are not taken into account, so that activation energy might be too high for it to actually occur
85
if temp increase
-ve --> exothermci
86
the enthalpy changes of solution of the magnesium halides show a trend from mgI2 to mgF2. Explain why it is difficult to predict whether the enthalpy change of solution becomes more exothermic or less exothermic down the group from mgF2 to mgI2.
1- halide ion gets larger down the group 2- lattice enthalpy less exothermic down group 3- halide ions has less attraction for mg 2+ 4- hydration enthalpy is less exothermic down group 5- halide ion has less attraction for h20 6- difficult to predict whether lattice enthalpy or hydration enthalpy has bigger effect
87
predict how the enthalpy change of hydratiomn of F- and Cl- would differ
Chemistry
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