energetics

Cards (9)

Standard enthalpy of combustion
The enthalpy change when one mole of a substance in its standard state is burned completely in oxygen under standard conditions
Standard enthalpy of formation
The enthalpy change when one mole of a substance is formed in its standard state from its pure elements in their standard states under standard conditions
What is bomb calorimetry?
Uses a machine called a bomb calorimeter to measure enthalpy changes of combustion. The process involves burning a sample of a compound in a sealed vessel and measuring the temperature.
How could a bomb calorimeter be inaccurate?
-Heat loss to surroundings
-Incomplete combustion may take place
-Loss of some reactant that may evaporate before combustion
How do you calculate energy changes?
q = mcΔT
m is the mass
Hesses law states 
Enthalpy change is independent of the pathway taken
Why are mean bond enthalpies inaccurate?
-Mean bond enthalpies are only valid in the gas phase and the reaction may not be in the gas phase
-Bond enthalpies depend on the molecule but mean bond enthalpies are general/ the average.
State the meaning of standard enthalpy change of reaction.
The enthalpy change that occurs for a reaction as written is at 100kPa/1atm and 298K/stated temperature.
Define the term mean bond enthalpy 
The enthalpy change required to break 1 mol bond in gaseous state averaged over a range of molecules