Energetics Flashcards
What is enthalpy change
The heat energy change measured under conditions of constant pressure
What are the standard conditions
100 kPa
298 k
What is the standard enthalpy change of combustion
The enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, and states
What is the standard enthalpy change of formation
The enthalpy change when one mole of substance is formed from its constituent elements under standard conditions and states
What is the calorimetry equation
Q=mcΔt
q = J
m = Kg
c = J/Kg.K
What does Hess’s law state
The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products.
Which ways do you draw the arrows in a hess cycle if we are measuring enthalpy of formation
Away from the elements
Which ways do you draw the arrows in a hess cycle if we are measuring enthalpy of combustion
Towards the elements
What is an allotrope
Pure carbon can exist in a number of forms at room temp. They are allotropes of carbon
What is mean bond enthalpy?
The average energy need to break a particular bond (The energy required to break a C—H bond can vary from molecule to molecule so an average is used)
How is enthalpy worked out
energy lost / gained (q) / moles
