Developing Fuels (DF) Flashcards
enthalpy change definition
energy transferred to and from the surroundings
enthalpy change =
sum of products - sum of reactants
standard conditions
enthalpy change can be affected by temperature, pressure and concentration
converting Celcius to Kelvin
add 273
standard enthalpy change of a reaction
enthalpy change when molar quantities of reactants react together under standard conditions
energy transferred =
specific heat capacity x mass x temperature change
standard enthalpy change of combustion
enthalpy change that occurs when a mole of a substance is burnt completely in oxygen under standard conditions
standard enthalpy change of formation
enthalpy change when one mole of a compound is formed from its elements, under standard states and standard conditions. use of enthalpy cycle
standard enthalpy change of neutralisation
measured from the energy given out when acids react with alkalis is aqueous solution under standard conditions.
name the different types of standard enthalpy change
reaction, neutralisation, formation, combustion
Hess’s Law
enthalpy change for any chemical reaction is independent of the intermediate stages, as long as the initial and final conditions are the same for each route
why carbon?
Unique electronic structure, meaning it would need to lose or gain 4 electrons to become stable, which is too much. so when carbon forms compounds they are covalent rather than ionic
catenation
carbon forms strong covalent bonds with itself to make chains/rings
difference between aromatic and aliphatic compounds
aromatic - containing an benzene ring, aliphatic - does not contain a benzene ring
functional group
modifiers that are responsible for the characteristic chemical reactions of molecules
structural isomer
same molecular formula but different structural formula
cycloalkanes
general formula CnH2n,
rules for naming branched alkanes
- find longest chain of carbons
- identify the side chains
- name side chains adding -yl
- keep number infront of prefix as low as possible
- multiple chains - alphabetic order, multiple of same chain - prefix di or tri
eg: 2,2-dimethylpropane
bond enthalpy
amount of energy needed to break one mole of a bond to give separate atoms in gaseous state.
higher bond enthalpies
shorter bond length, more bonds (double, triple) because there are more attractive forces from the electrons.
(bond) enthalpy change
sum of bonds broken - sum of bonds made
homogenous catalyst
when reactants and catalyst are in the same physical state
heterogeneous catalyst
when reactants and catalyst are in different physical state.
why is catalyst poisoning bad
no longer function properly, poison molecules are absorbed onto catalyst surface - catalyst cannot catalyse a poison therefore become inactive, active sites blocked.
