1.4 Energetics Flashcards
What is standard enthalpy changes?
When 1 mole of a compound is formed from its elements under standard conditions
what is standard enthalpy change of combustion?
will always be exothermic as burning relases heat
Combustion enthalpy must always start with 1 mole of what substance you are burning
what is an enthalpy change?
Bonds broken - bonds formed
describe exothermic
Energy released from formation is more then energy needed to break bonds
Describe endothermic
energy absorbed to break bonds is greater than energy released from making them
what is bond dissociation enthalpy
The enthalpy change needed to break a covalent bond with all species in a gaseous state
what is mean bond enthalpy
The average values of the bond dissociation enthalpy taken from a range of different compounds
what is standard enthalpy change of reaction?
Enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions.
For example: N2(g) + 3H2(g) ➔ 2NH3(g) ΔH⦵r = 92 kJ mol-1.
what is standard enthalpy change of formation?
Enthalpy change when 1 mole of a compound forms from elements under standard conditions.
For example: C(s) + O2(g) ➔ CO2(g) ΔH⦵f = 394 kJ mol-1.
what is standard enthalpy change of combustion?
Enthalpy change when 1 mole of a substance combusts fully in oxygen under standard conditions.
For example: CH4(g) + 2O2(g) ➔ CO2(g) + 2H2O(l) ΔH⦵c = 890 kJ mol-1.
what is standard enthalpy change of neutralization?
Enthalpy change when 1 mole of a substance neutralises fully in oxygen under standard conditions.
For example: CH4(g) + 2O2(g) ➔ CO2(g) + 2H2O(l) ΔH⦵c = 890 kJ mol-1.
define enthalpy
a heat or energy change under constant pressure
explain why a reaction would be exothermic
bond breaking releases energy and bond forming absorbs energy
more bonds broken means more energy released then formed
what is Hess’s law?
enthalpy change of a reaction at constant pressure is independent to the route taken.
