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21 Thermochemistry

Q 6. Thermochemistry

QuestionAnswer
thermochemistry study of the relationship of energy to chemistry
Bond energy is the average energy required to break one mole of a particular covalent bond & to separate the neutral atoms completely from each other.
Law of Conservation of energy Energy cannot be created or destroyed it, it just changes from one form to another.
enthalpy the heat content of a system measure at constant pressure
heat of reaction heat change when the number of moles of reactants indicated in the balanced equation for the reaction react completely.
heat of combustion of a substance is heat change when one mole of the substance is completely burned in excess oxygen
heat of formation the amount of heat given out or taken in when 1 mole of a compound is formed from its elements in their standard states
Kilogram Calorific Value heat energy given off when 1kg of the fuel is completely burned in oxygen
Hess's Law the total heat involved in a reaction is equal to the sum of the individual steps.
Avagadro's number the number of particles in one mole of a substance
Hydrocarbon a compound that contains Carbon & Hydrogen only
Fossil Fuels Fuels that are formed from the remains of plants and animals that lived millions of years ago.
Saturated compound One in which there are only single bonds between the atoms in the molecule.
Homologous series compounds of similar chemical properties, showing graduations in physical properties, Having a general formula, similar method of preparation & differing by a CH2 unit.
Structural Isomers are compounds with the same molecular formula but different structural formula
Alkyl Group An Alkane molecule that has had a Hydrogen removed e.g. Methyl - CH3, Ethyl - C2H5
Dimethyl two methyl groups
Alkene a hydrocarbon that contains a double bond between the atoms in the molecule.
Alkane a hydrocarbon that contains single bonds between the atoms in the molecule.
Alkyne a hydrocarbon that contains a triple bond between the atoms in the molecule.
Meth- one carbon atom in a compound
Eth- 2 Carbon atoms in a compound
Prop- 3 Carbon atoms in a compound
But- 4 Carbon atoms in a compound
Pent- 5 Carbon atoms in a compound
Hex- 6 Carbon atoms in a compound
Hept- 7 Carbon atoms in a compound
Oct- 8 Carbon atoms in a compound
Non- 9 Carbon atoms in a compound
Dec- 10 Carbon atoms in a compound
Aliphatic compound An organic compound that consists of open/closed chains of carbon atoms that resemble them in chemical properties.
Aromatic compounds Compounds that contain a benzene ring structure in their molecules
Benzene C6H6, A six carbon ring structure held together by bonds of equal lenght neither single or double bond lenght.
Auto-ignition is premature explosion of the petrol-air mixture before normal ignition of the mixture by a spark.
Octane Number is the measure of the tendency of a fuel to resist knocking, Reference Heptane Octane number = 0 & 2,2,4, trimethylpentane Octane number = 100
Catalytic Cracking Breakdown of long-chain hydrocarbon molecules by heat & catalysts into short-chain hydrocarbon molecules which are in greater demand
Isomerisation Changing straight chain alkanes into their highly branched short chain isomers
Dehydrocyclisation Straight chain alkanes are converted into cyclic/ring compounds and hydrogen gas is given off (Ring formation & removal of Hydrogen)
Heat of neutralisatioon heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base
Organic Chemistry the study of compounds of carbon
Unsaturated compound one that contains one or more double or triple bonds between the atoms in the molecule
Test for unsaturation decolourises Bromine water
Combustion of Ethene burns with a yellow luminous, slightly smoky flame
Combustion of Ethyne burns with a bright smoky flame & loads of soot particles formed.
Fractional Distillation Heating the Crude oil and separating out the different various parts based on their boiling points, compounds with similar boiling points are called fractions.
Exothermic Heat is produced, given out, temperature rises.
Endothermic Heat is absorbed, taken in, temperature drops.
Heat given out mass x specific heat capacityx rise in temperature
Created by: Ms O'Farrell
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