Hess's Law Flashcards
need t also add in about the practicals in hess’s law and enthalpy - talk about practical skills
need t also add in about the practicals in hess’s law and enthalpy - talk about practical skills
What does the principle of conservation of energy state
Energy cannot be created or destroyed, only changes from one form into another
What does Hess’s Law state
The enthalpy change for a chemical reaction is independent of the route taken and depends only on the initial and final states
Why is Hess’s law useful
It can be used to calculate the enthalpy changes of reactions that cannot be carried out in reality
What is the mean bond enthalpy
It is a measure of the energy required to break one mole of a covalent bond measured in the gaseous state in kJ mol^-1 averaged across many compounds containing the bond
Bond breaking is…
Endothermic
Bond making is…
Exothermic
How do mean bond enthalpies relate to the strength of covalent bonds
The higher the mean bond enthalpy the higher the strength of the covalent bond
How does length vary between single, double and triple covalent bonds
Single = longest Triple = shortest
How does strength vary between single, double and triple covalent bonds
Single = weakest Triple= strongest
Why is the bond enthalpy in an F-F bond lower than expected
The bond is very short and there are Repulsionen between the lone pairs of electrons on the F atoms.
What state do all the reactants have to be in when calculating the mean bond enthalpy
Gas
