Chapter 4 - Energetics Flashcards
Define Enthalpy change
Enthalpy change (ΔH) is the heat change of a system, measured at a constant pressure. Measured in kJ/mol
State Hess’s Law
The enthalpy change in converting reactants to products is the same regardless of the route taken provided the initial and final conditions are the same
Define Standard enthalpy of formation
The enthalpy change when 1 mole of compound is formed from its constituent elements with all reactants and products in standard states under standard conditions
Define Standard enthalpy of combustion
The enthalpy change when 1 mole of a substance is burned completely in excess oxygen with all reactants and products in their standard states under standard conditions
What must you make sure happens when calculating enthalpy values and standard combustion reactions
The combustion must be 1 mole
Why is the enthalpy of FORMATION of elements always 0?
Examples:
Thermal decomposition reactions (heating of reactants dont know temp change is due to heat supplies of the decomposition process)
Define average bond enthalpy
The energy required to break one mole of a specific type of bond in a gaseous molecule
When calculating Delta H using mean bond enthalpy what state are all the substances in?
GAS
State 2 limitation of using mean bond enthalpies
Variations in strength of one kind of bond in different molecules
One of the reactants or products is not gaseous
