Energetics Flashcards
Define enthalpy change.
Heat energy change at a constant pressure.
What is an exothermic reaction?
Energy is released to the surroundings.
What is an endothermic reaction?
Energy is taken in from the surroundings.
In an exothermic reaction what is the value of the ∆H?
Negative
In an endothermic reaction what is the value of the ∆H?
Positive
Define standard enthalpy of combustion.
The enthalpy change when one mole of a substance burns completely in oxygen with all substances in their standard states.
Define standard enthalpy of formation.
The enthalpy change when one mole of the compound is formed from its constituent elements under standard conditions and in their standard states.
What is the enthalpy of formation
of an element?
0
What does incomplete combustion lead to?
Soot (carbon), carbon monoxide and water. It will be less exothermic than complete combustion.
What are the standard conditions?
100kPa
298K
Energy change equation?
q = mc∆T
Define Hess’s Law?
The total enthalpy change is independent of the route taken.
Enthalpy change of formation equation?
Reaction = Products - Reactants.
Enthalpy change of combustion equation?
Reaction = Reactants - Products.
Define mean bond energies.
The enthalpy needed to break the covalent bond into gaseous atoms averaged over different molecules.
