Chemical quantities and energetics

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  • Created on: 15-05-14 18:58
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Chemical Quantities
- Atom: smallest particle of an element
- Element: simplest chemical
- Ion: an atom, or group of atoms, which has become electrically
charged by loss or gain of electrons
- Molecule: particle containing two or more atoms joined
- Compound: chemical containing two or more elements
chemically combined together
- Empirical formula: shows simplest whole-number ratio of
atoms of different elements in one molecule of a
- Molecular formula: shows the number of atoms of the
different elements in one molecule
- Relative atomic mass (Ar): average mass of an atom of the element relative to 1/12 of the mass of
an atom of C-14 (N.B. 1 mole of gas takes up 24dm3)
- Relative formula mass (Mr): sum of all relative atomic masses of all atoms in its molecular formula
- Avogadro constant: number of atoms/molecules in one mole of a substance (i.e. 1 mole of oxygen
contains 6 x 1023 O2 molecules)
- Percentage yield: (actual yield ÷ theoretical yield) x 100
- Atom economy: (mass of atoms in desired product ÷ mass of atoms in all reactants) x 100
- Spectator ions: take no part in the reaction
Reactions of acids
- With metals above H in reactivity series: metal + acid salt + hydrogen
- Metal (hydr)oxide + acid salt + water
- Carbonate + acid salt + water + carbon dioxide
- Acid + alkali salt + water
- Precipitation: when precipitate forms
- Displacement: when more reactive chemical displaces less reactive one from compound

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- Formation (Hof): enthalpy change which occurs when 1 mole of the compound is formed from its
elements under standard conditions, and with everything in its standard state.
- Combustion (Hoc): full combustion of 1 mole of the compound in oxygen under standard
conditions, and with everything in its standard state.…read more

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Hesss Law
- = Enthalpy change of a reaction is the same regardless of the route taken provided the conditions
remain constant
- We can calculate Hf from Hc, and we can calculate Hreaction from Hf
- E.g.…read more


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