Thermochemistry Flashcards
Thermochemistry
Electronegativity
An atom’s ability to attract bonding electrons to itself
First ionisation energy
The minimum amount of energy required to remove one mole of loosely held electrons from one mole of gaseous atoms.
Electronegativity trend (across a period)
Electronegativity increases across a period because the nuclear charge increases, meaning electrons are pulled closer to the more electronegative atom.
Electronegativity trend (down a group)
Electronegativity decreases down a group since increasing the distance of the bonding electrons from the nucleus decreases the attraction. Also, the shielding effect reduces the pull of the nucleus on the bonding electron pair.
First ionisation energy (across a period)
First ionisation energy increases across a period because the greater number of protons (higher nuclear charge) attract the orbiting electrons more strongly, therefore increasing the energy required to remove one of the electrons.
First ionisation energy trend (down a group)
First ionisation energy decreases down a group due to the greater number of shells, so the valence electrons further from the protons, which attract them less strongly there fore requiring less energy to remove them.
Also, outer electrons are shielded from the pull of the positive protons in the nucleus by the electron shells that are closer to the nucles. This makes it easier to remove the outer electron and less energy is needed.
Atomic radius (__ atom and __- ion)
__ and the __- ion have the same number of protons but when the __ atom gains an electron(s), there is increased electron-electron repulsion in the valence energy level. As a result, the electrons move further apart, so the __- ion has a larger radius than the __ atom.
Atomic radius (__ atom and __+ ion)
__ and the __+ ion have the same number of protons but when the __ atom loses an electron(s), there is decreased electron-electron repulsion in the valence energy level. As a result, the electrons move closer together, so the __+ ion has a smaller radius than the __ atom.
Entropy of the system and Entropy of the surroundings (spontaneous)
The entropy of the system increases since __ moles of __ reactants formed __ moles of __ products. This means there is greater dispersal of energy and matter in the system.
Since the reaction is endothermic/exothermic, the heat absorbs/releases heat energy from/into the surroundings, so particles in the surroundings lose/gain heat energy. This results in less/greater dispersal of energy and matter in the surroundings, so entropy of the surrounding decreases/increases.
(if spontaneous) Since this reaction is spontaneous, the increase of the entropy of the system must outweigh the decrease of the entropy of the surroundings, making the total entropy change positive.
If something was liquid state instead of solid state
Heat energy is released when converting a liquid to a solid. Therefore if ___ formed were in the liquid state rather than as a solid, less energy would be released in its products, having a higher enthalpy
ΔfusH°
(enthalpy of fusion): the energy needed to convert 1 mole of solid to liquid at its melting point
ΔsubH°
(enthalpy of sublimation): the energy needed to convert 1 mole of solid to gas
ΔvapH°
(enthalpy of vaporisation): the energy needed to convert 1 mole of liquid to gas at its boiling point.
ΔrH°
(enthalpy of reaction): change in enthalpy during a chemical reaction
ΔfH°
(standard enthalpy of formation): the energy released/absorbed when1 mole of product is made from its constituent elements.
ΔcH°
(standard enthalpy of combustion): the heat energy released when 1 mole of substance is completely burnt in oxygen.
