Energy Flows Linked to Chemical Change Flashcards
How to predict energy of a reaction
compare the bonds broken versus the bonds formed, compare the strength of the bonds formed versus broken (bond order, sigma versus pi, atomic radii)
What phase should a reaction be in to determine Reaction Enthalpy Change?
gas in order to ignore IMFs
Thermochemical expression
balanced chemical equation together with the value of the reaction standard enthalpy
Change in standard state enthalpy
standard state enthalpy of pure, unmixed products minus the standard state enthalpy of pure unmixed reactants
What does a negative ∆H standard mean?
the reaction is exothermic
What does a positive ∆H standard mean?
the reaction is endothermic
Hess’ Law
if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps
What happens to the enthalpy changes if a reaction is flipped?
It becomes negative (multiplied by -1)
Standard formation enthalpy
the enthalpy change for a reaction in which exactly one mole of a pure substance in a specific state is formed from free elements in their most stable states under standard state conditions
Equation for ∆rHº
∑∆fHºproducts - ∑∆fHºreactants
What type of reaction is enthalpy?
a state reaction
If the number of bonds broken> the number of bonds formed is it most likely exothermic or endothermic?
Endothermic
