Energetics Flashcards
When bonds between atoms in the reactants are broken the reaction is…
Endothermic
When atoms rearrange and form new bonds in the products this reaction is…
Exothermic
What is the definition of exothermic reaction?
-releases energy to the surroundings
Bond formation is endothermic/exothermic
Exothermic
A reaction is overall exothermic if..
The energy released in bond formation in the products is great than that absorbed by bond breaking in the reactants
In an endothermic reaction energy…
Is absorbed from the surroundings
A reaction is overall endothermic if…
The energy absorbed to break bonds in the reactants is greater than the energy released to form bonds in the products
What is a catalyst?
-a substance that increases the rate of reaction without being used up
How does a catalyst work?
-provides an alternate reaction pathway with a lower activation energy
What is enthalpy change
Heat energy change @ constant pressure
What are the standard conditions?
- 298K
- 1moldm3
- 101kPa
What is mean bond enthalpy?
-the enthalpy change required to break 1 mol of a covalent bond in the gas phase, averaged over a range of compounds
Why are the values for ΔH using mean bond enthalpies approximate?
- as they have been calculated using averaged bond enthalpies, not specific to actual bonds in our question.
What is Hess’s Law?
- the enthalpy change of a reaction is independent of the route taken by the reaction
Why is the enthalpy change of formation fo an element in its standard state = 0?
- By definition
