Energetics Flashcards
What’s enthalpy change
Heat energy change measured under constant pressure
What are standard conditions
100 kPa and 298K
Define standard enthalpy of formation
The enthalpy change which occurs when one mole of the compound is made from its constituent elements under standard conditions and when everything is in its standard state
Define standard enthalpy of combustion
The enthalpy change which occurs when one mole of the compound is burnt completely in oxygen under standard conditions and when everything is in its standard state
What is the equation for calorimetry
E = MCØ
What is the mass in a calorimetry equation
Mass of the substance that has a temperature change (most probably water)
Define Hess’ Law
The total enthalpy change is constant, regardless of the route taken under constant pressure
Define mean bond enthalpy
The enthalpy change when one mole of a covalent bond is broken, averaged over different compounds
Why do values from bond enthalpies and Hess’ Law differ
Bond enthalpies only use average values of bond energies as values can differ for each bond depending on the compound it’s in
What is bond dissociation enthalpy
Enthalpy change required to break a covalent bond with all species in the gaseous state
What is an exothermic reaction
When more energy is released from forming new bonds
What is an endothermic reaction
When more energy is taken from breaking bonds
