C4 - Energetics Flashcards
In an exothermic reaction
Heat is given out to surroundings
In an endothermic reaction
Heat is taken in from surroundings
What is the standard enthalpy of combustion
Enthalpy change when one mole of a substance is completely burned in excess oxygen under standard conditions
What is standard enthalpy of formation
Enthalpy change when one mole of a compound is formed from its elements on their standard states under standard conditions
specific heat capacity formula
Q = MC ∆t
Q is
The heat/energy
M is
The mass
C is
The specific heat capacity of a substance
∆t is
Change in temperature
Hess’ law is:
Enthalpy change of a reaction is independent of the route taken
What is mean bond enthalpy
Average energy needed to break one mole of a particular bond
Why do mean bond enthalpy values differ from those determined using Hess’ law
Because mean bond enthalpy is an average value taken from a variety of compounds with different properties, affecting the energy required
