Chimstry Unit 2 Keywords

Keywords and their definitions.

The mechanisms listed are there to test my knowledge and to establish the difference between them, they are not asked as key words in the exams.

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  • Created by: MK
  • Created on: 04-04-13 10:09
Enthalpy
Heat change at constant temperature.
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Enthalpy change
Heat change at constant pressure.
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Enthalpy change of formation
The enthalpy change when one mole of a compound is forms from its constituent elements under standard conditions (298K and 100kPa), all reactants and products being in their standard state.
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Enthalpy change of combustion
The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions (298K and 100kPa), all reactants and products being in their standard state.
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Hess's law (1)
Hess's law states that the enthalpy change for a chemical reaction is the same whatever route is taken from reactants to products.
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Hess's law (2)
Hess's law is a special case of the first law of thermodynamics, which states that energy can neither be created or destroyed but can be converted from one form into another.
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Bond enthalpy
Bond enthalpy of a particular covalent bond is the enthalpy change when one mole of the bonds are broken.
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Mean bond enthalpy
The mean bond enthalpy of a particular covalent bond is the enthalpy change when one mole of the bonds are broken averaged over a range of compounds bearing that bond.
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Activation energy
The minimum energy required by the colliding particles for the reaction to occur.
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Rate of reaction
The change in concentration (mass/volume or mole/volume) of reactants or products per unit time.
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Catalysts (what they are)
Catalysts are substances which affect the rate of chemical reactions without being chemically changed themselves.
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Catalysts (what they do)
Catalysts speed up the rare of reaction by providing an alternate reaction pathway which has a lower activation energy.
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Dynamic equilibrium (only attained in a CLOSED SYSTEM)
The rate of forward reaction equals the rate of the reverse reaction so that the concentration of products and reactants remains constant (not 0). Dynamic indicates that the reaction is still proceeding in both directions.
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Le Chatlier's Principle
''An equilibrium will shift in a direction to oppose any change imposed on it.''
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Nucleophile
An electron pair donor to an electron deficient atom, usually carbon.
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Isomers
Isomers have the same molecular formula with different arrangement of atoms.
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Structural isomers
Same molecular formula with different structural formula.
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Stereoisomers
Same molecular formula, same structural formula with different arrangement of bonds within space.
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Geometrical isomers
Occur about a C=C bond (due to the restricted rotation about C=C), when there are two DIFFERENT groups on each carbon atom.
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Nucleophilic substitution
A partially positively charged carbon atom is attacked by a nucleophile. The nucleophile replaces one of the groups (usually the halogen.)
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Elimination
The removal of a halogen from a haloalkane, when a base attacks a hydrogen to bond with. end products are H-base, alkene and negative halogen.
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Free radical substitution
The reaction between an alkane and halogen when UV radiation is emitted on them (or when temperatures are about 500 degrees C). Forms a haloalkane. and H-X
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Electrophilic addition.
Carbon-carbon double bond is saturated (alkene ---> alkane). Initially, an electrophile attacks the double bond to form a bond with one of the carbons to form a carbocation.
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Electrophile
An electron deficient species (ion/atom/compound) that attacks areas of high electron density in another reactant.
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Other cards in this set

Card 2

Front

Heat change at constant pressure.

Back

Enthalpy change

Card 3

Front

The enthalpy change when one mole of a compound is forms from its constituent elements under standard conditions (298K and 100kPa), all reactants and products being in their standard state.

Back

Preview of the back of card 3

Card 4

Front

The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions (298K and 100kPa), all reactants and products being in their standard state.

Back

Preview of the back of card 4

Card 5

Front

Hess's law states that the enthalpy change for a chemical reaction is the same whatever route is taken from reactants to products.

Back

Preview of the back of card 5
View more cards

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