3.1.4 Energetics Flashcards
Define the term standard enthalpy of formation.
The enthalpy change when 1 mole of a compound is formed from its constiuent elements in their standard states under standard conditions.
What type of reaction is the standard enthalpy of combustion?
Exothermic
ΔH = always -ve
Define the term standard enthalpy of combustion.
The enthalpy change when one mole of a substance is burned completely in oxygen to form its oxides in their standard states, under standard conditions
Give 2 reasons why you would expect the enthalpy of combustion calculated in a laboratory to be different to the theoretical value.
- Substance not burnt completely, incomplete combustion occurs
- Some heat energy lost to the surroudings
State Hess’ Law.
The enthalpy change of a reaction is independent of the route taken
What is meant by mean bond enthalpy?
The average energy required to break a specific covalent bond, taken from a range of compounds
What equations are used in calorimetry?
q = mcΔT
ΔH = q/n
What occurs in reactions when ΔH is:
a) -ve
b) +ve
a) more energy released from when bonds are formed
b) more energy taken in from when bonds are broken
