R1.2 Energy Cycles in Reactions Flashcards
(16 cards)
What is a chemical bond?
A force of attraction between two atoms.
What type of process is bond breaking?
Endothermic process.
What is another term for bond dissociation enthalpy?
Bond enthalpy or bond energy.
What type of process is bond formation?
Exothermic process.
What is average bond energy?
The energy needed to break one mole of bonds in a gaseous molecule averaged over a variety of similar compounds.
How is the average bond enthalpy of C-H in methane calculated?
By taking the bond dissociation enthalpy for the whole molecule and dividing it by the number of C-H bonds.
What does Hess’s Law state?
The total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place.
depends only on chemical nature and physical states
What does the first law of thermodynamics relate to?
The Law of Conservation of Energy.
What is the definition of standard enthalpy of formation?
The enthalpy change when one mole of a compound is formed from its elements under standard conditions.
What is the general expression for standard enthalpy change of combustion?
ΔHꝊ = ∑ΔHcꝊ(reactants) - ∑ΔHcꝊ(products).
since energy of reactants ‘should’ be higher since evrything in the world loses energy over time
What is a Born-Haber cycle used for?
To calculate lattice enthalpy for ionic compounds.
What is the basic principle of a Born-Haber cycle?
To show all the steps needed to turn atoms into gaseous ions and from gaseous ions into the ionic lattice.
What is the significance of Hess’s Law in thermodynamics?
It allows the calculation of enthalpy changes that cannot be found experimentally.
What type of energy cycle is used for combustion products in Hess’s Law?
The combustion products are always placed at the bottom of the diagram.
activation energy
the minimum energy required to start a recation by breaking the bond sin the reactants
