Physical Thermodynamics Exam Reported Questions Well Answered.
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Course
NA 701
Institution
NA 701
Endothermic reaction - correct answer To break bonds, the surroundings need to give energy to the molecule. The bonds gains energy, as they take in energy so have a positive sign. The system loses energy so gets colder
Exothermic reaction - correct a...
Endothermic reaction - correct answer To break bonds, the surroundings need
to give energy to the molecule. The bonds gains energy, as they take in energy so have a positive sign.
The system loses energy so gets colder
Exothermic reaction - correct answer To make bonds, the molecule give energy
to the surroundings. The bonds lose energy, as they give out energy so have a negative sign. The system
gains energy so gets hotter
What are the standard conditions - correct answer 298K, 1 moldm3 and
100kPa pressure
Enthalpy of atomisation - correct answer The enthalpy when one mole of
gaseous atoms is formed from the element in its standard state
Na(s) --> Na(g) - for a metal
1/2Cl2(g) --> Cl(g) - for a non metal
First ionisation enthalpy - correct answer The energy required to form one
mole of gaseous unipositive ions from one mole of gaseous atoms
Na(g) --> Na+(g) + e-
First electron affinity - correct answer The enthalpy change when one mole of
gaseous atoms each gain an electron to form one mole of gaseous negative ions
Cl(g) + e- --> Cl-(g)
Second electron affinity - correct answer The enthalpy change when one mole
of gaseous ions each gain an electron to form one mole of gaseous negative ions
O-(g) + e- --> O2-(g)
, Lattice enthalpy of formation - correct answer The enthalpy change when one
mole of an ionic solid is formed from gaseous ions
Na+(g) + Cl-(g) --> NaCl(s)
Lattice enthalpy of dissociation - correct answer The enthalpy change when
one mole of an ionic solid is separated into its gaseous ions
NaCl(s) --> Na+(g) + Cl-(g)
Features of born haber cycle - correct answer Arrows going up = endothermic
= will result in changes above
Arrows going down = exothermic = will result in changes below
Symbols and state symbols need to be written on each level
Arrow are not to scale
Constructing a born haber cycle - correct answer Start in the standard states
Atomise metal
Ionise metal (if ion has more than one charge, second ionisation has to be shown)
Atomise non metal
First electron affinity non metal to become an ion (if ion has more than one charge, second electron
affinity has to be shown)
Lattice enthalpy of formation of two ionised species, CAN CHECK THE CALCULATED NUMBER IS RIGHT BY
STARTING ANYWHERE ON THE CYCLE, ANSWER SHOULD BE ZERO
Born haber cycle - correct answer
Na2O born haber cycle - what additional steps are needed - correct answer
Second electron affinity
Oxygen forms O2- ion
2 sodium atoms are needed in the ionic lattice so need to double the atomisation enthalpy and
ionisation enthalpies
2 sodiums will each need to lose an electron in the ionisation phase
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