thermodynamic exam questions Flashcards
in terms of electrostatic forces suggest why the electron affinity of fluorine has a negative value
- there is an attraction between the nucleus and electrons
- energy is released when the electron is gained
Explain why the theoretical enthalpy of lattice dissociation is higher than the value from the Born-haber cycle
- has some covalent character
- theoretical lattice enthalpy assumes its perfectly ionic
the theoretical enthalpy of lattice dissociation for silver chloride is 770klmol-1. Explain why this is less than the value for silver fluoride
- chloride ion is larger than the fluoride ion
- attraction between Ag+ and Cl- weaker
H2O(s)->H2O(L)
use your knowledge of bonding to explain why the enthalpy change is positive
- hydrogen bonds need to be broken
- so energy is released
two properties that influence the value of a lattice enthalpy calculated using the perfect ionic model
- size of the ions
- charge of the ions
suggest why the first electron affinity of oxygen is an endothermic process
making bonds
equation of enthalpy of solution of MgCl2
MgCl2 -> Mg2+(aq) + 2Cl-(aq)
Why is the enthalpy of hydration of Ca2+ less exothermic than Mg2+
- Ca2+ larger charge compared to size
- higher electron density
why is the standard entropy of CO2 greater than carbon
gas is more disordered than a solid
Explain why the enthalpy of hydration becomes less exothermic from Li+ to K+
- size of ion increases
- the electrostatic attraction between metal ion and o- of water decreases attraction between lone pair o and + ion decreases
why is the enthalpy of lattice formation of AgI a smaller numerical value than the value calculated
- AgI contains covalent character
- forces are stronger
why is the value for enthalpy of hydration for the chloride ion more negative than the bromide ion
- Cl- are smaller
- force of attraction between Cl- and water is stronger
- Cl- attraction +H of water
explain why gibbs energy change for dissolving KCl in water is -ve, even though enthalpy is +ve
- entropy change is +ve
- 1mol solid -> 2 mol aq
explain why entropy is 0 when the temperature is zero kelvin
- at 0K particles are stationary
- no disorder
explain why Mg+ attract water molecules
- water is polar
- Mg+ is attracted to delta - on O-
why is the enthalpy of solution of MgO not found in any data books
reacts with water
Explain why fluoride ion is larger than a sodium ion
- fluoride ion has a lower nuclear charge
- weaker attraction between fluoride ions outer electron and nucleus
why could the lattice dissociation be more or less than the value obtained from the perfect ionic model
- greater
- has covalent character
how is the lattice formation of NaCl compare with that of NaF
- less exothermic
- f- smaller ions
- so attraction of halide ion to Na+ is weaker
why is the second electron affinity an endothermic process
negative 1- ion, repels electrons being added
why is the electron affinity of chlorine an exothermic change
net attraction between the chlorine nucleus and extra electron
what would the value of enthalpy of lattice dissociation of silver chloride be compared to silver bromide
- greater than
- bromide is a larger ion
- attracted more strongly to the silver ions
