enthalpy and entropy Flashcards
write the equation for the lattice enthalpy of magnesium bromide and calculate the lattice enthalpy of magnesium bromide (1)
Mg2+(g)+2Br-(g)->MgBr2(s)
the first ionisation energy of sodium is more endothermic than that of potassium explain why (2)
- sodium - atomic radius is smaller / fewer shells
- nuclear attraction increases / outer electrons experience more attraction
the lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide explain why (2)
- for sodium ions ionic radius of Na+ is smaller
- Na+ has a stronger attraction to O2-
explain what is meant by the term enthalpy change of hydration (2)
(enthalpy change when)✓
1 mole of gaseous ions react✓
OR 1 mole of hydrated/aqueous ions are formed ✓
gaseous ions dissolve in water
OR gaseous ions form aqueous/hydrated ions ✓
predict how the enthlpy changes of hydration of F- and Cl- would differ explain your answer (2)
*Correct comparison of Δhyd linked to sizes
ΔhydH(F−) more negative/exothermic (than
ΔhydH(CΓ))
AND
F− has smaller size (than Cl−) ✓
Comparison of attraction between ions and water
F− OR smaller sized ion linked to greater attraction
to H2O ✓
The student carries out a second experiment using 150 cm3 of distilled water instead of
100 cm3 of distilled water. The mass of concentrated sulfuric acid is the same as in the
first experiment.
Predict and explain the effect, if any, of the larger volume of water on the following:
* The temperature change, ΔT
* The calculated value of ΔsolH for H2SO4. (4)
Predictions
ΔT is less
AND
ΔsolH is the same ✓
Reason for ΔT less
(same) energy/heat spread over larger volume (of
water) ✓
ΔT = 7°C ✓
Reason for ΔsolH same
Same energy released per mole of H2SO4 ✓
define the term enthalpy chnge of hydration (2)
(enthalpy change for) 1 mole of gaseous ions OR 1 mole
of hydrated ions / aqueous ions ✔
gaseous ions forming aqueous / hydrated ions
The entropy change of solution of K2SO4 is +225 J K−1 mol−1.
i. Suggest, in terms of the states of the particles involved, why this entropy change is
positive (1)
Aqueous particles are more disordered than solid
(particles)
OR
Solid particles are more ordered than aqueous
(particle
define the term lattice enthalpy (2)
The enthalpy change that accompanies) the formation
of one mole of an (ionic) compound from its gaseous
ions (under standard conditions)
predict the oder of melting points from lowest to highest for NaBr, KI and RbCl from lowest to highest explain why (3)
- KI,RbCl,NaBr
Attraction and ionic size linked:
Greater attraction from smaller ions / closer ions /
larger
charge density ✔
Comparison needed
Energy AND attraction / breaking bonds linked:
More energy / heat to overcome attraction (between
ions)
OR
More energy / heat to break (ionic) bonds
explain what is meant by the term enthalpy change of solution (1)
solution: (enthalpy change for)
1 mole of a compound / substance / solid / solute
dissolving in water
explain the differences between these enthalpy changes of hydration between an aluminium ion, calcium ion, magnesium ion,and a sodium ion (3)
Comparison of size
Ca2+ > Mg2+
Comparison of charge
Na+ < Mg2+ < Al3+
Comparison of attraction between ions
size AND charge linked to greater attraction to H2O
Student 2 carries out the same experiment but uses twice the mass of CaCl2. All other
quantities are very similar to Student 1’s experiment.
Predict any differences between the temperature change and the calculated value of
ΔsolH from the experiments of the two students. Explain your reasoning. (2)
Temperature change is double / × 2 / 63 °C
AND
ΔsolH is the same
Twice the energy produced in the same volume
AND
ratio of energy produced to mass or number of moles is
the same is the same
Lattice enthalpies give an indication of the strength of ionic bonding.
How would the lattice enthalpies of magnesium chloride and calcium chloride differ?
Explain your answer (3)
Lattice enthalpy of MgCl2 is more exothermic than CaCl2
… (1)
because magnesium ion / Mg2+ is smaller (than calcium
ions / Ca2+)
OR Mg2+ has a greater charge density … (1)
… therefore the attraction between Mg2+ and Cl
− is
greater (than between Ca2+ and Cl
−) (1)
wo changes are described below.
For each change,
- write an equation, including state symbols,
- state and explain how the entropy changes.
i. The reaction of aqueous barium nitrate with aqueous sodium sulfate
Equation
Ba(NO3)2(aq) + Na2SO4(aq) → BaSO4(s)
+ 2NaNO3(aq) ✓
Entropy change and explanation
entropy decreases OR entropy change negative
AND
(BaSO4) solid / ppt has less disorder / more order
/ fewer ways of arranging energy / less freedom /
less random particles / dispersal of energy ✓
describe the change that accompanies the standard enthalpy chane of atomiation or iodine and explain (2)
Equation
½ I2(s) → I(g) ✓
state symbols required
Entropy change and explanation
entropy increases OR entropy change positive
AND
gas has more disorder / less order / more ways
of arranging energy / more freedom / more
random particles / more dispersal of energy
The enthalpy and entropy changes of a reaction both have a negative sign.
Discuss how the feasibility of this reaction will change as the temperature increases.(2)
Feasibility AND ΔG
Reaction becomes / is less feasible / not feasible
AND
ΔG increases
OR ΔG becomes / is less negative / more positive
OR ΔG > 0 OR ΔH − TΔS > 0
OR ΔH − TΔS becomes / is less negative / more
positive
OR ΔH > TΔS ✔
OR TΔS becomes / is more negative than ΔH ✔
Effect on TΔS
TΔS becomes more negative OR TΔS decreases
OR −TΔS becomes more positive OR −TΔS increases
OR magnitude of TΔS increases
OR | TΔS | increases ✔
