Energetics Flashcards
Enthalpy change definition
Heat energy change at constant pressure
Standard conditions
100kpa
298k
1mold-3 solution
Mean bond enthalpy definition
Energy required to break one mole of covalent bonds into gaseous atoms averaged over a range of different compounds
Calculating bond enthalpy
Left- right
Enthalpy of formation definition
Energy required when one mole of substance is formed from its elements in standard conditions with all the reactants and products been in their standard state
Calculating enthalpy of formation
Right - left
Enthalpy of combustion definition
Energy when one mole of substance is completely burned in excess oxygen under standard conditions with all reactants and products being in their standard state
Calculating enthalpy of combustion
Left - right
Suggest why enthalpy of combustion may be difficult to measure
Incomplete combustion may occur
Some fuel may evaporate
Hess law definition
Enthalpy change for reaction is the same no matter what route is taken from reactants to products
Calorimetry equations
Q = mc change in t( kelvin or degrees)
Change in h =Q/N
Use total volume but limiting moles
Inaccuracy in calorimetery
Heat lawsuit to surroundings, so add
Incomplete combustion of fuel
Some fuel evaporates
Insulate so reduces heat loss
Reduce distance between flame and beaker
Plus sleeve around flame to protect it from droughts
Steps to Measure enthalpy change using a cooling curve
- Record the initial temperature for three minutes every 30 seconds before adding reactants together.
- This is to establish an accurate initial temperature
- Makes reactants and require temperature every 30 seconds until a trend is seen
- Plot a graph of temperature the time
- Extrapolate the cooling curve back to point of audition
- to establish a theoretical temperature change
