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42 Cards in this Set
- Front
- Back
Exothermic Reaction |
A reaction that gives out energy and heats the surroundings. |
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Endothermic Reaction |
A reaction that takes in energy and cools the surroundings. |
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3 things for Standard conditions: |
- 298K / 25 degrees C - A standard pressure of 1 atmosphere (atm) - A standard concentration of 1 moldm -3 for solutions. |
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Standard States |
The physical state of a substance under standard conditions. This may be a pure solid, liquid or gas. |
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Standard Enthalpy Change for a Reaction ∆rHѲ298 |
The enthalpy change when one molar quantities of reactants as stated in the equation react together under standard conditions.
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Kelvin (K) |
273K = 0 degrees C. |
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Standard Enthalpy Change of Combustion ∆cHѲ298 |
The enthalpy change that occurs when 1 mole of a substance is burnt completely in excess oxygen under standard conditions in standard states. |
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Standard Enthalpy Change of Formation ∆fHѲ298 |
The enthalpy change when 1 mole of a compound is formed from its elements under standard conditions in standard states. |
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Standard Enthalpy Change of Neutralisation ∆neutHѲ298 |
The enthalpy change when 1 mole of hydrogen ions react with 1 mole of hydroxide ions to form 1 mole of water under standard conditions and in solutions containing 1 moldm-3. |
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Specific Heat Capacity of a substance (c) |
The amount of energy needed to raise the temperature of 1g of a substance by 1K.
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Aromatic Compounds |
Compounds that contain one or more benzene rings. |
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Aliphatic Compounds |
Compounds that do not contain any benzene rings. |
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Functional Group |
Modifiers that are responsible for the characteristic chemical reactions of molecules. |
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Saturated |
Hydrocarbons containing the maximum number of hydrogen atoms possible, with no double or triple bonds between carbon atoms. |
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Molecular Formula |
The number of atoms of each element in a compound. |
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Homologous Series |
A series of compounds in which all members have the same general molecular formula. |
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Average Bond Enthalpy |
The average quantity of energy needed to break a particular bond. |
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Cracking |
Any reaction in which a larger molecule is made into smaller molecules. |
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Unsaturated |
Any organic compound that has a double or triple bond between carbon atoms. |
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Hess's Law |
The enthalpy change for a particular reaction will always be the same and is independent of the pathway taken providing that starting and finishing conditions are the same. |
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Catalyst |
A substance that speeds up a reaction but can be chemically unchanged at the end. A catalyst always lowers the activation enthalpy and can provide an alternative pathway for the reaction. |
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Catalysis |
The process of speeding up a chemical reaction using a catalyst. |
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Homogeneous Catalysis |
When the reactants and products are in the same physical state as the catalyst. |
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Heterogeneous Catalysis |
When the reactants and products are in different physical states to the catalyst. |
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Catalyst poison |
Poison adsorbs (sticks) more strongly than reactants So reactant molecules can't bond with the surface of the catalyst. |
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Electrophile |
A species which can act as an electron pair acceptor and is attracted to a region of high electron density such as a double bond. They are usually + or delta + |
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Carbocation |
An ion with a positively-charged carbon atom. |
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Addition reaction |
A reaction where two or more molecules react to form a single larger molecule. |
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Polymerisation |
Small molecules called monomers join together to produce long chain polymers. |
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Hydrocarbon |
A compound which contains hydrogen and carbon atoms ONLY. |
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Arene |
An aromatic hydrocarbon. |
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Test for Unsaturation |
Shake the substance with bromine water. The bromine is decolourised (red-brown to colourless) if the substance is unsaturated. |
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Structural Isomer |
Same molecular or chemical formula Different structural arrangement of atoms |
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Stereoisomerism |
Occurs in compounds with C=C double bond. Owing to the lack of free rotation (locked by the pi bond) E/X pair where each C of the C=C has a hydrogen atom |
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Elastomer |
A polymer which can be deformed and later return to its original size and shape |
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Steps in Heterogeneous Catalysis |
Gas molecules are adsorbed (stick) onto the catalyst surface. Bonds in reactants weaken and break New bonds and molecules (products) form Products diffuse away from the catalyst surface. |
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Bond-breaking |
Endothermic |
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Bond-making |
Exothermic |
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Why a reaction is exothermic or gives out heat? |
Bonds broken in reactants - energy in New bonds formed in products - energy released Greater energy released than taken in so overall there is an output of energy = exothermic. |
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Why experimental enthalpy values are different from those in a data book? |
Bond enthalpies are only average values and vary between molecules Chemicals are not in their standard states in the given example. |
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Sigma bond |
The end-on overlap of electron orbitals (s with s, s with p, p with p) so that the shared pair of electrons is an area of increased electron density along the internuclear line between the atoms. |
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Pi bond |
The lateral overlap of p electron orbitals so that the shared pair of electrons consists of two areas of increased electron density above and below the internuclear line between the atoms. |