UNIT 2 - DEFINITIONS Flashcards
(31 cards)
DEFINE enthalpy
The heat content of a system at a constant pressure
DEFINE system
An isolated part of the universe, just reactants and products. The surroundings is everything other than the reactants and products
DEFINE exothermic reaction
Releases energy into the surroundings, temperature rise and DH is negative
DEFINE endothermic reaction
A reaction which takes energy from the surroundings, temperature drop, DH is positive
DEFINE standard enthalpy of combustion
The enthalpy change when one mole of a substance is completely burned under excess oxygen under standard conditions.
DEFINE standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions
DEFINE average bond enthalpy
The energy required to break one mole of a bond in a gaseous species under standard conditions
DEFINE principle of conservation of energy
Energy cannot be created nor destroyed, only transferred
DEFINE Hess’ Law
The enthalpy change of a reaction is independent of the route from the reactants to the products
DEFINE rate of reaction
Change in concentration of a reagent or product measured against time
DEFINE catalyst
A substance that increases rate of reaction without itself being used up in the process. It provides an alternative reaction pathway with lower Ea.
DEFINE homogeneous catalyst
A catalyst in the same state as its reactants. It takes an active part in the reaction.
I.E. Sulphuric Acid in the esterification of alcohols
DEFINE heterogeneous catalyst
A catalyst in a different physical state to the reactants.
I.E. Iron in the Haber process, N and H sticks to it adsorption and this holds them in place as they react. Desorb after.
DEFINE homologous series
A series of compounds with the same functional group
DEFINE functional group
The atom/group that gives a molecule its characteristic properties
DEFINE displayed formula
Shows all the atoms and bonds in a compound
DEFINE structural isomer
Same molecular formula but different structure
DEFINE sigma bond
A bond made by the end-to-end over lap of s or p orbitals
DEFINE complete combustion
Combustion that occurs with excess oxygen
DEFINE incomplete combustion
Combustion that occurs with insufficient oxygen
DEFINE radical
A species with an unpaired valence electron
DEFINE homolytic fission
Breaking of a covalent bond to produce two radicals
DEFINE initiation step
The reaction that starts the process. A molecule is turned into two radicals by homolytic fission
DEFINE propogation
The reaction by which the process continues to grow, keep reforming a new radical
