DF.2 Flashcards
Enthalpy cycles and Hess' law
What is tool called that we use to measure enthalpy changes indirectly?
Enthalpy cycles.
What enthalpy change do we often use to indirectly work out enthalpy change of formation?
Enthalpy changes of combustion
What does Hess’ law state about enthalpy changes?
The enthalpy change for any chemical reaction is independent of the pathway taken, as long as the initial and final conditions are the same.
What is the comparison between the total enthalpy change of the indirect route and the enthalpy change of the direct route?
They must be the same.
What does the law of conservation of energy state?
Energy cannot be created or destroyed.
How do you find the enthalpy change of a reversed reaction?
Just reverse the sign of the enthalpy change.
When would it be useful to use enthalpy change of formation to indirectly work out the enthalpy change of a reaction?
When it endothermic for example, endothermic reaction’s enthalpy change can’t be measured directly. Or in other reactions when it is difficult to measure the enthalpy change.
What is the general equation when calculating the enthalpy change using enthalpy changes of formation in a Hess’ cycle?
ΔHr⦵ = ΣΔHr⦵products - ΣΔHr⦵reactants Σ = sum of
