CH. 2.2 - ENTHALPY Flashcards
What is Enthalpy?
Enthalpy is the amount of energy in a system at a constant temperature
Can absolute enthalpy be measured?
No, which is why we use ΔH = ΔE + PΔV (we use Δ to calculate change in enthalpy)
At a constant pressure, ΔH (enthalpy change) of a system is = to…
the heat flowing into or out of a system:
ΔH = qₚ
What is latent heat?
the energy change associated with physical processes that involve a change of state
What are examples of endothermic state changes?
Melting, boiling, etc.
(solid —> liquid —> gas)
What are examples of exothermic state changes?
Condensation, freezing, etc.
(gas —> liquid —> solid)
If ΔH < 0, is the process EXOthermic or ENDOthermic?
exothermic
if ΔH > 0, is the process EXOthermic or ENDOthermic?
endothermic
What is Calorimetry?
the study of heat flow in physical and chemical processes
TRUE OR FALSE: a calorimeter and its contents will INCREASE in temperature during an EXOthermic process
TRUE
TRUE OR FALSE: a calorimeter and its contents will INCREASE in temperature during an ENDOthermic process
FALSE: the calorimeter and its contents will DECREASE
What is the Standard Enthalpy of Formation?
the enthalpy change that occurs when one mole of a substance is formed from elements in their standard states
ΔH* (element in standard state) = _____
0
What is Hess’s Law?
the enthalpy change for a reaction is the SUM of the enthalpy changes for the individual steps of the reaction
What is Bond Enthalpy (BE)?
the energy required to break one mole of a specific type of bond (double or triple) between 2 atoms
TRUE OR FALSE: Bond Enthalpy can be positive or negative because it can be both ENDO and EXOthermic
FALSE: bond enthalpy is always endothermic and therefore, always positive.
Why is Bond Enthalpy endothermic?
because it is the process of breaking bonds which means energy is absorbed and therefore endothermic
What is Total Bond Enthalpy (TBE)?
the energy required to break ALL of the bonds in one mole of gaseous compound
What is harder to break, a double bond or a triple bond?
triple bond (bond strength INCREASES with bond order)
