Thursday 13 May 2010
Enthalpy Change & profile diagrams
Exothermic = -
endothermic = +
Enthalp change = is the heat transferred in a reaction at constant pressure.
Unit one chemistry review - formula , equations and amount of substance --
Basic formulas:
Avogadro constant = 6.02 X 10^23
moles = mass of substance/ molar mass
moles= vol. X conc.
moles = vol. in dm3 /24 ( gas at r.t.p)
Percentage yeild = actual yeild / theoretical yeild X 100
% atom economy = Mr of desired product/ sum of Mr of all products X 100
Ex. question for finding molecular formula:
- For a compound whos molecular formula is CH2O, the molecular mass was found to be 180. what is its molecular formula ?
- Molecular formula = empirical formula X molecular mass/ empirical formula mass
so the molecular formula = CH2O X 180/30 = C6H12O6
Important definitions:
relative atomic mass : is the average mass of an atom of an element on a scale where an atom of carbon-12 is 12.
relative isotopic mass: is the mass of an atom of an isotope on a scale where an atom of carbon 12 is 12.
relative molecular mass: is the average mass of an atom of a molecule on a scale where carbon 12 is 12.